diff --git a/languageservice/src/complete.expressions.test.ts b/languageservice/src/complete.expressions.test.ts
index a8463ef..d6756d3 100644
--- a/languageservice/src/complete.expressions.test.ts
+++ b/languageservice/src/complete.expressions.test.ts
@@ -1268,7 +1268,7 @@ jobs:
 on: push
 jobs:
   a:
-    uses: ./reusable-workflow-with-outputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-outputs.yaml
   b:
     needs: [a]
     runs-on: ubuntu-latest
diff --git a/languageservice/src/complete.reusable-workflows.test.ts b/languageservice/src/complete.reusable-workflows.test.ts
index 79d1495..3fde8c0 100644
--- a/languageservice/src/complete.reusable-workflows.test.ts
+++ b/languageservice/src/complete.reusable-workflows.test.ts
@@ -21,7 +21,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
     with:
       |
 `;
@@ -49,7 +49,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
     with:
       username: monalisa
       |
@@ -74,7 +74,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
     secrets:
       |
 `;
@@ -102,7 +102,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
     secrets: |
 `;
     const result = await complete(...getPositionFromCursor(input), {fileProvider: testFileProvider});
@@ -117,7 +117,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
     secrets:
       envPAT: "myPAT"
       |
diff --git a/languageservice/src/context-providers/needs.test.ts b/languageservice/src/context-providers/needs.test.ts
index 88baecf..8cad20a 100644
--- a/languageservice/src/context-providers/needs.test.ts
+++ b/languageservice/src/context-providers/needs.test.ts
@@ -111,7 +111,7 @@ jobs:
 on: push
 jobs:
   a:
-    uses: ./reusable-workflow-with-outputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-outputs.yaml
 
   b:
     needs: [a]
diff --git a/languageservice/src/hover.reusable-workflow.test.ts b/languageservice/src/hover.reusable-workflow.test.ts
index a8d9459..d31330d 100644
--- a/languageservice/src/hover.reusable-workflow.test.ts
+++ b/languageservice/src/hover.reusable-workflow.test.ts
@@ -14,7 +14,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
     with:
       us|ername:
 `;
@@ -31,7 +31,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs-no-description.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs-no-description.yaml
     with:
       us|ername:
 `;
@@ -48,7 +48,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-outputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-outputs.yaml
   echo_outputs:
     runs-on: ubuntu-latest
     needs: build
diff --git a/languageservice/src/test-utils/test-file-provider.ts b/languageservice/src/test-utils/test-file-provider.ts
index 966d9f7..40e41aa 100644
--- a/languageservice/src/test-utils/test-file-provider.ts
+++ b/languageservice/src/test-utils/test-file-provider.ts
@@ -5,9 +5,9 @@ export const testFileProvider: FileProvider = {
   // eslint-disable-next-line @typescript-eslint/require-await
   getFileContent: async ref => {
     switch (fileIdentifier(ref)) {
-      case "monalisa/octocat/workflow.yaml@main":
+      case "monalisa/octocat/.github/workflows/workflow.yaml@main":
         return {
-          name: "monalisa/octocat/workflow.yaml",
+          name: "monalisa/octocat/.github/workflows/workflow.yaml",
           content: `
 on: workflow_call
 jobs:
@@ -31,9 +31,9 @@ jobs:
 `
         };
 
-      case "./reusable-workflow.yaml":
+      case "./.github/workflows/reusable-workflow.yaml":
         return {
-          name: "reusable-workflow.yaml",
+          name: ".github/workflows/reusable-workflow.yaml",
           content: `
 on: workflow_call
 jobs:
@@ -44,9 +44,9 @@ jobs:
 `
         };
 
-      case "./reusable-workflow-with-inputs.yaml":
+      case "./.github/workflows/reusable-workflow-with-inputs.yaml":
         return {
-          name: "reusable-workflow-with-inputs.yaml",
+          name: ".github/workflows/reusable-workflow-with-inputs.yaml",
           content: `
 on:
   workflow_call:
@@ -76,9 +76,9 @@ jobs:
   `
         };
 
-      case "./reusable-workflow-with-inputs-no-description.yaml":
+      case "./.github/workflows/reusable-workflow-with-inputs-no-description.yaml":
         return {
-          name: "reusable-workflow-with-inputs.yaml",
+          name: ".github/workflows/reusable-workflow-with-inputs.yaml",
           content: `
 on:
   workflow_call:
@@ -95,9 +95,9 @@ jobs:
   `
         };
 
-      case "./reusable-workflow-with-outputs.yaml":
+      case "./.github/workflows/reusable-workflow-with-outputs.yaml":
         return {
-          name: "reusable-workflow-with-outputs.yaml",
+          name: ".github/workflows/reusable-workflow-with-outputs.yaml",
           content: `
 on:
   workflow_call:
diff --git a/languageservice/src/validate.expressions.test.ts b/languageservice/src/validate.expressions.test.ts
index a237787..dbf83ec 100644
--- a/languageservice/src/validate.expressions.test.ts
+++ b/languageservice/src/validate.expressions.test.ts
@@ -635,7 +635,7 @@ jobs:
         fail-fast: true
         matrix:
           node: [14, 16]
-      uses: ./reusable-workflow-with-inputs.yaml
+      uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
       with:
         username: User-\${{ strategy.fail-fast }}
   `;
@@ -654,7 +654,7 @@ jobs:
       strategy:
         matrix:
           node: [14, 16]
-      uses: ./reusable-workflow-with-inputs.yaml
+      uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
       with:
         username: \${{ matrix.node }}
   `;
diff --git a/languageservice/src/validate.ts b/languageservice/src/validate.ts
index b00380a..cf27522 100644
--- a/languageservice/src/validate.ts
+++ b/languageservice/src/validate.ts
@@ -143,11 +143,29 @@ async function additionalValidations(
       }
     }
 
+    // Validate step uses field format
+    if (isString(token) && token.range && validationDefinition?.key === "step-uses") {
+      validateStepUsesFormat(diagnostics, token);
+    }
+
+    // Validate action metadata (inputs, required fields) for regular steps
     if (token.definition?.key === "regular-step" && token.range) {
       const context = getProviderContext(documentUri, template, root, token.range);
       await validateAction(diagnostics, token, context.step, config);
     }
 
+    // Validate job-level reusable workflow uses field format
+    if (
+      isString(token) &&
+      token.range &&
+      key &&
+      isString(key) &&
+      key.value === "uses" &&
+      parent?.definition?.key === "workflow-job"
+    ) {
+      validateWorkflowUsesFormat(diagnostics, token);
+    }
+
     // Allowed values coming from the schema have already been validated. Only check if
     // a value provider is defined for a token and if it is, validate the values match.
     if (token.range && validationDefinition) {
@@ -198,6 +216,307 @@ function invalidValue(diagnostics: Diagnostic[], token: StringToken, kind: Value
   }
 }
 
+/**
+ * Validates the format of a step's `uses` field.
+ *
+ * Valid formats:
+ * - docker://image:tag
+ * - ./local/path
+ * - .\local\path (Windows)
+ * - {owner}/{repo}@{ref}
+ * - {owner}/{repo}/{path}@{ref}
+ */
+function validateStepUsesFormat(diagnostics: Diagnostic[], token: StringToken): void {
+  const uses = token.value;
+
+  // Empty uses value
+  if (!uses) {
+    diagnostics.push({
+      message: "`uses' value in action cannot be blank",
+      severity: DiagnosticSeverity.Error,
+      range: mapRange(token.range),
+      code: "invalid-uses-format"
+    });
+    return;
+  }
+
+  // Docker image reference - always valid format
+  if (uses.startsWith("docker://")) {
+    return;
+  }
+
+  // Local action path - always valid format
+  if (uses.startsWith("./") || uses.startsWith(".\\")) {
+    return;
+  }
+
+  // Remote action: must be {owner}/{repo}[/path]@{ref}
+  const atSegments = uses.split("@");
+
+  // Must have exactly one @
+  if (atSegments.length !== 2) {
+    addStepUsesFormatError(diagnostics, token);
+    return;
+  }
+
+  const [repoPath, gitRef] = atSegments;
+
+  // Ref cannot be empty
+  if (!gitRef) {
+    addStepUsesFormatError(diagnostics, token);
+    return;
+  }
+
+  // Split by / or \ to get path segments
+  const pathSegments = repoPath.split(/[\\/]/);
+
+  // Must have at least owner and repo (both non-empty)
+  if (pathSegments.length < 2 || !pathSegments[0] || !pathSegments[1]) {
+    addStepUsesFormatError(diagnostics, token);
+    return;
+  }
+
+  // Check if this is a reusable workflow reference (should be at job level, not step)
+  // Path would be like: owner/repo/.github/workflows/file.yml
+  if (pathSegments.length >= 4 && pathSegments[2] === ".github" && pathSegments[3] === "workflows") {
+    diagnostics.push({
+      message: "Reusable workflows should be referenced at the top-level `jobs.<job_id>.uses` key, not within steps",
+      severity: DiagnosticSeverity.Error,
+      range: mapRange(token.range),
+      code: "invalid-uses-format"
+    });
+    return;
+  }
+}
+
+function addStepUsesFormatError(diagnostics: Diagnostic[], token: StringToken): void {
+  diagnostics.push({
+    message: `Expected format {owner}/{repo}[/path]@{ref}. Actual '${token.value}'`,
+    severity: DiagnosticSeverity.Error,
+    range: mapRange(token.range),
+    code: "invalid-uses-format"
+  });
+}
+
+/**
+ * Validates the format of a job's `uses` field (reusable workflow reference).
+ *
+ * Valid formats:
+ * - {owner}/{repo}/.github/workflows/{filename}.yml@{ref}
+ * - {owner}/{repo}/.github/workflows/{filename}.yaml@{ref}
+ * - {owner}/{repo}/.github/workflows-lab/{filename}.yml@{ref}
+ * - {owner}/{repo}/.github/workflows-lab/{filename}.yaml@{ref}
+ * - ./.github/workflows/{filename}.yml
+ * - ./.github/workflows/{filename}.yaml
+ * - ./.github/workflows-lab/{filename}.yml
+ * - ./.github/workflows-lab/{filename}.yaml
+ */
+function validateWorkflowUsesFormat(diagnostics: Diagnostic[], token: StringToken): void {
+  const uses = token.value;
+
+  // Local workflow reference
+  if (uses.startsWith("./.github/workflows/") || uses.startsWith("./.github/workflows-lab/")) {
+    // Cannot have @ version for local workflows
+    if (uses.includes("@")) {
+      addWorkflowUsesFormatError(diagnostics, token, "cannot specify version when calling local workflows");
+      return;
+    }
+
+    // Must have .yml or .yaml extension
+    if (!uses.endsWith(".yml") && !uses.endsWith(".yaml")) {
+      addWorkflowUsesFormatError(
+        diagnostics,
+        token,
+        "workflow file should have either a '.yml' or '.yaml' file extension"
+      );
+      return;
+    }
+
+    // Must be at top level of .github/workflows/ or .github/workflows-lab/ (no subdirectories)
+    const pathParts = uses.split("/");
+    if (pathParts.length !== 4) {
+      // Expected: ".", ".github", "workflows" or "workflows-lab", "filename.yml"
+      addWorkflowUsesFormatError(
+        diagnostics,
+        token,
+        "workflows must be defined at the top level of the .github/workflows/ directory"
+      );
+      return;
+    }
+
+    // Filename cannot be just the extension
+    const filename = pathParts[3];
+    if (filename === ".yml" || filename === ".yaml") {
+      addWorkflowUsesFormatError(diagnostics, token, "invalid workflow file name");
+      return;
+    }
+
+    return;
+  }
+
+  // Remote workflow reference: must have @ for version
+  const atSegments = uses.split("@");
+  if (atSegments.length === 1) {
+    addWorkflowUsesFormatError(diagnostics, token, "no version specified");
+    return;
+  }
+  if (atSegments.length > 2) {
+    addWorkflowUsesFormatError(diagnostics, token, "too many '@' in workflow reference");
+    return;
+  }
+
+  const [pathPart, version] = atSegments;
+
+  // Version cannot be empty
+  if (!version) {
+    addWorkflowUsesFormatError(diagnostics, token, "no version specified");
+    return;
+  }
+
+  // Must contain .github/workflows or .github/workflows-lab path
+  const workflowsMatch = pathPart.match(/\.github\/workflows(-lab)?\//);
+  if (!workflowsMatch || workflowsMatch.index === undefined) {
+    addWorkflowUsesFormatError(diagnostics, token, "references to workflows must be rooted in '.github/workflows'");
+    return;
+  }
+
+  // Split to get owner/repo and path
+  const pathIdx = workflowsMatch.index;
+  const nwoPart = pathPart.substring(0, pathIdx);
+  const workflowPath = pathPart.substring(pathIdx);
+
+  // Validate NWO part: must be owner/repo/
+  const nwoSegments = nwoPart.split("/").filter(s => s.length > 0);
+  if (nwoSegments.length !== 2) {
+    addWorkflowUsesFormatError(
+      diagnostics,
+      token,
+      "references to workflows must be prefixed with format 'owner/repository/' or './' for local workflows"
+    );
+    return;
+  }
+
+  // Validate owner and repo names
+  const [owner, repo] = nwoSegments;
+  const nwoError = validateNWO(owner, repo);
+  if (nwoError) {
+    addWorkflowUsesFormatError(diagnostics, token, nwoError);
+    return;
+  }
+
+  // Validate ref/version format
+  const refError = validateRefName(version);
+  if (refError) {
+    addWorkflowUsesFormatError(diagnostics, token, refError);
+    return;
+  }
+
+  // Validate workflow path is at top level
+  const workflowPathParts = workflowPath.split("/");
+  if (workflowPathParts.length !== 3) {
+    // Expected: ".github", "workflows" or "workflows-lab", "filename.yml"
+    addWorkflowUsesFormatError(
+      diagnostics,
+      token,
+      "workflows must be defined at the top level of the .github/workflows/ directory"
+    );
+    return;
+  }
+
+  // Must have .yml or .yaml extension
+  const filename = workflowPathParts[2];
+  if (!filename.endsWith(".yml") && !filename.endsWith(".yaml")) {
+    addWorkflowUsesFormatError(
+      diagnostics,
+      token,
+      "workflow file should have either a '.yml' or '.yaml' file extension"
+    );
+    return;
+  }
+
+  // Filename cannot be just the extension
+  if (filename === ".yml" || filename === ".yaml") {
+    addWorkflowUsesFormatError(diagnostics, token, "invalid workflow file name");
+    return;
+  }
+}
+
+function addWorkflowUsesFormatError(diagnostics: Diagnostic[], token: StringToken, reason: string): void {
+  diagnostics.push({
+    message: `Invalid workflow reference '${token.value}': ${reason}`,
+    severity: DiagnosticSeverity.Error,
+    range: mapRange(token.range),
+    code: "invalid-workflow-uses-format"
+  });
+}
+
+/**
+ * Validates the git ref/version format.
+ * Based on Launch's ValidateRefName function.
+ */
+function validateRefName(refname: string): string | undefined {
+  if (refname.length === 0) {
+    return "no version specified";
+  }
+
+  // Cannot be the single character '@'
+  if (refname === "@") {
+    return "version cannot be the single character '@'";
+  }
+
+  // Cannot have certain invalid characters or sequences
+  const invalidSequences = ["?", "*", "[", "]", "\\", "~", "^", ":", "@{", "..", "//"];
+  for (const seq of invalidSequences) {
+    if (refname.includes(seq)) {
+      return `invalid character '${seq}' in version`;
+    }
+  }
+
+  // Cannot begin or end with a slash '/' or a dot '.'
+  if (refname.startsWith("/") || refname.endsWith("/") || refname.startsWith(".") || refname.endsWith(".")) {
+    return "version cannot begin or end with a slash '/' or a dot '.'";
+  }
+
+  // No slash-separated component can begin with a dot '.' or end with the sequence '.lock'
+  const components = refname.split("/");
+  for (const component of components) {
+    if (component.startsWith(".") || component.endsWith(".lock")) {
+      return `invalid version: ${refname}`;
+    }
+  }
+
+  // No ASCII control characters or whitespace
+  // eslint-disable-next-line no-control-regex
+  if (/[\x00-\x1f\x7f]/.test(refname)) {
+    return "version cannot have ASCII control characters";
+  }
+
+  if (/\s/.test(refname)) {
+    return "version cannot have whitespace";
+  }
+
+  return undefined;
+}
+
+/**
+ * Validates owner and repository names.
+ * Based on Launch's ValidateNWO function.
+ */
+function validateNWO(owner: string, repo: string): string | undefined {
+  // Owner name: can have word chars, dots, and hyphens
+  // \w in JS regex is [a-zA-Z0-9_]
+  if (!/^[\w.-]+$/.test(owner)) {
+    return "owner name must be a valid repository owner name";
+  }
+
+  // Repository name: can have word chars, dots, and hyphens
+  if (!/^[\w.-]+$/.test(repo)) {
+    return "repository name is invalid";
+  }
+
+  return undefined;
+}
+
 function getProviderContext(
   documentUri: URI,
   template: WorkflowTemplate,
diff --git a/languageservice/src/validate.uses-format.test.ts b/languageservice/src/validate.uses-format.test.ts
new file mode 100644
index 0000000..67777fc
--- /dev/null
+++ b/languageservice/src/validate.uses-format.test.ts
@@ -0,0 +1,872 @@
+import {DiagnosticSeverity} from "vscode-languageserver-types";
+import {validate} from "./validate";
+import {createDocument} from "./test-utils/document";
+import {clearCache} from "./utils/workflow-cache";
+
+beforeEach(() => {
+  clearCache();
+});
+
+describe("validate uses format", () => {
+  describe("valid formats", () => {
+    it("standard org/repo@ref", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("org/repo with path @ref", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/aws/ec2@main
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("org/repo with deep path @ref", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/aws/nested/deep/path@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("docker image", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: docker://alpine:3.8
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("docker image with registry", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: docker://gcr.io/my-project/my-image:latest
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("local path with ./", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: ./my-action
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("local path with ./ and subdirectories", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: ./.github/actions/my-action
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("local path with .\\ (Windows)", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: .\\my-action
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("SHA ref", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("branch ref", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: owner/repo@feature/my-branch
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+  });
+
+  describe("invalid formats", () => {
+    it("missing @ref", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Expected format {owner}/{repo}[/path]@{ref}. Actual 'actions/checkout'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 5, character: 12},
+            end: {line: 5, character: 28}
+          },
+          code: "invalid-uses-format"
+        }
+      ]);
+    });
+
+    it("empty ref", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Expected format {owner}/{repo}[/path]@{ref}. Actual 'actions/checkout@'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 5, character: 12},
+            end: {line: 5, character: 29}
+          },
+          code: "invalid-uses-format"
+        }
+      ]);
+    });
+
+    it("missing org/owner", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: checkout@v4
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Expected format {owner}/{repo}[/path]@{ref}. Actual 'checkout@v4'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 5, character: 12},
+            end: {line: 5, character: 23}
+          },
+          code: "invalid-uses-format"
+        }
+      ]);
+    });
+
+    it("empty owner", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: /repo@v4
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Expected format {owner}/{repo}[/path]@{ref}. Actual '/repo@v4'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 5, character: 12},
+            end: {line: 5, character: 20}
+          },
+          code: "invalid-uses-format"
+        }
+      ]);
+    });
+
+    it("empty repo", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: owner/@v4
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Expected format {owner}/{repo}[/path]@{ref}. Actual 'owner/@v4'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 5, character: 12},
+            end: {line: 5, character: 21}
+          },
+          code: "invalid-uses-format"
+        }
+      ]);
+    });
+
+    it("multiple @ symbols", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4@extra
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Expected format {owner}/{repo}[/path]@{ref}. Actual 'actions/checkout@v4@extra'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 5, character: 12},
+            end: {line: 5, character: 37}
+          },
+          code: "invalid-uses-format"
+        }
+      ]);
+    });
+
+    it("just a name with no slash", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: checkout
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Expected format {owner}/{repo}[/path]@{ref}. Actual 'checkout'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 5, character: 12},
+            end: {line: 5, character: 20}
+          },
+          code: "invalid-uses-format"
+        }
+      ]);
+    });
+
+    it("empty uses value", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: ""
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toContainEqual({
+        message: "`uses' value in action cannot be blank",
+        severity: DiagnosticSeverity.Error,
+        range: {
+          start: {line: 5, character: 12},
+          end: {line: 5, character: 14}
+        },
+        code: "invalid-uses-format"
+      });
+    });
+
+    it("reusable workflow in step", async () => {
+      const input = `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: owner/repo/.github/workflows/test.yml@main
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message:
+            "Reusable workflows should be referenced at the top-level `jobs.<job_id>.uses` key, not within steps",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 5, character: 12},
+            end: {line: 5, character: 54}
+          },
+          code: "invalid-uses-format"
+        }
+      ]);
+    });
+  });
+});
+
+describe("workflow uses format validation", () => {
+  beforeEach(() => {
+    clearCache();
+  });
+
+  describe("valid formats", () => {
+    it("local workflow path", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: ./.github/workflows/test.yml
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("local workflow path with yaml extension", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: ./.github/workflows/test.yaml
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("remote workflow with version", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("remote workflow with sha ref", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@abc123
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("remote workflow with branch ref", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@main
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("remote workflow with yaml extension", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yaml@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("local workflows-lab path", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: ./.github/workflows-lab/test.yml
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("local workflows-lab path with yaml extension", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: ./.github/workflows-lab/test.yaml
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+
+    it("remote workflows-lab with version", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows-lab/test.yml@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([]);
+    });
+  });
+
+  describe("invalid formats", () => {
+    it("remote workflow missing version", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Invalid workflow reference 'owner/repo/.github/workflows/test.yml': no version specified",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 3, character: 10},
+            end: {line: 3, character: 47}
+          },
+          code: "invalid-workflow-uses-format"
+        }
+      ]);
+    });
+
+    it("local workflow with version", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: ./.github/workflows/test.yml@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message:
+            "Invalid workflow reference './.github/workflows/test.yml@v1': cannot specify version when calling local workflows",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 3, character: 10},
+            end: {line: 3, character: 41}
+          },
+          code: "invalid-workflow-uses-format"
+        }
+      ]);
+    });
+
+    it("missing .github/workflows path", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/test.yml@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message:
+            "Invalid workflow reference 'owner/repo/test.yml@v1': references to workflows must be rooted in '.github/workflows'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 3, character: 10},
+            end: {line: 3, character: 32}
+          },
+          code: "invalid-workflow-uses-format"
+        }
+      ]);
+    });
+
+    it("invalid file extension", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.txt@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message:
+            "Invalid workflow reference 'owner/repo/.github/workflows/test.txt@v1': workflow file should have either a '.yml' or '.yaml' file extension",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 3, character: 10},
+            end: {line: 3, character: 50}
+          },
+          code: "invalid-workflow-uses-format"
+        }
+      ]);
+    });
+
+    it("no extension", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message:
+            "Invalid workflow reference 'owner/repo/.github/workflows/test@v1': workflow file should have either a '.yml' or '.yaml' file extension",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 3, character: 10},
+            end: {line: 3, character: 46}
+          },
+          code: "invalid-workflow-uses-format"
+        }
+      ]);
+    });
+
+    it("just a ref", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: test.yml@v1
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message:
+            "Invalid workflow reference 'test.yml@v1': references to workflows must be rooted in '.github/workflows'",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 3, character: 10},
+            end: {line: 3, character: 21}
+          },
+          code: "invalid-workflow-uses-format"
+        }
+      ]);
+    });
+
+    it("local without .github/workflows", async () => {
+      const input = `on: push
+jobs:
+  test:
+    uses: ./workflows/test.yml
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+      expect(result).toEqual([
+        {
+          message: "Invalid workflow reference './workflows/test.yml': no version specified",
+          severity: DiagnosticSeverity.Error,
+          range: {
+            start: {line: 3, character: 10},
+            end: {line: 3, character: 30}
+          },
+          code: "invalid-workflow-uses-format"
+        }
+      ]);
+    });
+
+    describe("invalid ref/version format", () => {
+      it("empty version after @", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message: "Invalid workflow reference 'owner/repo/.github/workflows/test.yml@': no version specified",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 48}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("version with invalid character ?", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@v1?
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner/repo/.github/workflows/test.yml@v1?': invalid character '?' in version",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 51}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("version with double dots", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@v1..v2
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner/repo/.github/workflows/test.yml@v1..v2': invalid character '..' in version",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 54}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("version ending with dot", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@v1.
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner/repo/.github/workflows/test.yml@v1.': version cannot begin or end with a slash '/' or a dot '.'",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 51}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("version starting with slash", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@/v1
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner/repo/.github/workflows/test.yml@/v1': version cannot begin or end with a slash '/' or a dot '.'",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 51}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("version ending with .lock", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@refs/heads/main.lock
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner/repo/.github/workflows/test.yml@refs/heads/main.lock': invalid version: refs/heads/main.lock",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 68}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("version with whitespace", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@v1 && rm -rf
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner/repo/.github/workflows/test.yml@v1 && rm -rf': version cannot have whitespace",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 60}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("version with backslash", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/test.yml@v1\\1
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner/repo/.github/workflows/test.yml@v1\\1': invalid character '\\' in version",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 52}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+    });
+
+    describe("invalid owner/repo names", () => {
+      it("owner with invalid characters", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner*/repo/.github/workflows/test.yml@v1
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner*/repo/.github/workflows/test.yml@v1': owner name must be a valid repository owner name",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 51}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("repo with invalid characters", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo!name/.github/workflows/test.yml@v1
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner/repo!name/.github/workflows/test.yml@v1': repository name is invalid",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 55}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("owner with spaces", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner name/repo/.github/workflows/test.yml@v1
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message:
+              "Invalid workflow reference 'owner name/repo/.github/workflows/test.yml@v1': owner name must be a valid repository owner name",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 55}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+    });
+
+    describe("invalid workflow filename", () => {
+      it("filename is just .yml", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/.yml@v1
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message: "Invalid workflow reference 'owner/repo/.github/workflows/.yml@v1': invalid workflow file name",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 46}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("filename is just .yaml", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: owner/repo/.github/workflows/.yaml@v1
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message: "Invalid workflow reference 'owner/repo/.github/workflows/.yaml@v1': invalid workflow file name",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 47}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+
+      it("local workflow filename is just .yml", async () => {
+        const input = `on: push
+jobs:
+  test:
+    uses: ./.github/workflows/.yml
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+        expect(result).toEqual([
+          {
+            message: "Invalid workflow reference './.github/workflows/.yml': invalid workflow file name",
+            severity: DiagnosticSeverity.Error,
+            range: {
+              start: {line: 3, character: 10},
+              end: {line: 3, character: 34}
+            },
+            code: "invalid-workflow-uses-format"
+          }
+        ]);
+      });
+    });
+  });
+});
diff --git a/languageservice/src/validate.workflow-references.test.ts b/languageservice/src/validate.workflow-references.test.ts
index ec1c446..6932fa9 100644
--- a/languageservice/src/validate.workflow-references.test.ts
+++ b/languageservice/src/validate.workflow-references.test.ts
@@ -43,7 +43,7 @@ on: push
 
 jobs:
   build:
-    uses: monalisa/octocat/workflow.yaml@not-a-branch
+    uses: monalisa/octocat/.github/workflows/workflow.yaml@not-a-branch
 `;
     const result = await validate(createDocument("wf.yaml", input), {
       fileProvider: testFileProvider
@@ -58,7 +58,7 @@ jobs:
             line: 5
           },
           end: {
-            character: 53,
+            character: 71,
             line: 5
           }
         }
@@ -72,7 +72,7 @@ on: push
 
 jobs:
   build:
-    uses: monalisa/octocat/workflow.yaml@main
+    uses: monalisa/octocat/.github/workflows/workflow.yaml@main
 `;
     const result = await validate(createDocument("wf.yaml", input), {
       fileProvider: testFileProvider
@@ -87,7 +87,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow.yaml
+    uses: ./.github/workflows/reusable-workflow.yaml
 `;
     const result = await validate(createDocument("wf.yaml", input), {
       fileProvider: testFileProvider
@@ -102,7 +102,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
     secrets:
       envPAT: pat
 `;
@@ -119,7 +119,7 @@ jobs:
             line: 5
           },
           end: {
-            character: 46,
+            character: 64,
             line: 5
           }
         }
@@ -133,7 +133,7 @@ on: push
 
 jobs:
   build:
-    uses: ./reusable-workflow-with-inputs.yaml
+    uses: ./.github/workflows/reusable-workflow-with-inputs.yaml
     with:
       username: monalisa
     secrets: