diff --git a/actions-languageservice/src/complete.test.ts b/actions-languageservice/src/complete.test.ts
index b9c20ca..b18949e 100644
--- a/actions-languageservice/src/complete.test.ts
+++ b/actions-languageservice/src/complete.test.ts
@@ -373,4 +373,51 @@ jobs:
       end: {line: 6, character: 17}
     });
   });
+
+  describe("completes with indentation", () => {
+    it("default indentation", async () => {
+      const input = `on: push
+jobs:
+  build:
+    step|`;
+      const result = await complete(...getPositionFromCursor(input));
+
+      // Sequence
+      expect(result.filter(x => x.label === "steps").map(x => x.textEdit?.newText)).toEqual(["steps:\n  - "]);
+
+      // Mapping
+      expect(result.filter(x => x.label === "env").map(x => x.textEdit?.newText)).toEqual(["env:\n  "]);
+
+      // Value
+      expect(result.filter(x => x.label === "timeout-minutes").map(x => x.textEdit?.newText)).toEqual([
+        "timeout-minutes: "
+      ]);
+
+      // One-of
+      expect(result.filter(x => x.label === "concurrency").map(x => x.textEdit?.newText)).toEqual(["concurrency"]);
+    });
+
+    it("custom indentation", async () => {
+      // Use 3 spaces to indent
+      const input = `on: push
+jobs:
+   build:
+      step|`;
+      const result = await complete(...getPositionFromCursor(input));
+
+      // Sequence
+      expect(result.filter(x => x.label === "steps").map(x => x.textEdit?.newText)).toEqual(["steps:\n   - "]);
+
+      // Mapping
+      expect(result.filter(x => x.label === "env").map(x => x.textEdit?.newText)).toEqual(["env:\n   "]);
+
+      // Value
+      expect(result.filter(x => x.label === "timeout-minutes").map(x => x.textEdit?.newText)).toEqual([
+        "timeout-minutes: "
+      ]);
+
+      // One-of
+      expect(result.filter(x => x.label === "concurrency").map(x => x.textEdit?.newText)).toEqual(["concurrency"]);
+    });
+  });
 });
diff --git a/actions-languageservice/src/complete.ts b/actions-languageservice/src/complete.ts
index 0477b19..1dfe643 100644
--- a/actions-languageservice/src/complete.ts
+++ b/actions-languageservice/src/complete.ts
@@ -16,6 +16,7 @@ import {getContext, Mode} from "./context-providers/default";
 import {getWorkflowContext, WorkflowContext} from "./context/workflow-context";
 import {nullTrace} from "./nulltrace";
 import {findToken} from "./utils/find-token";
+import {guessIndentation} from "./utils/indentation-guesser";
 import {mapRange} from "./utils/range";
 import {transform} from "./utils/transform";
 import {Value, ValueProviderConfig} from "./value-providers/config";
@@ -94,18 +95,23 @@ export async function complete(
     }
   }
 
-  const values = await getValues(token, keyToken, parent, valueProviderConfig, workflowContext);
+  const indentation = guessIndentation(newDoc, 2, true); // Use 2 spaces as default and most common for YAML
+  const indentString = " ".repeat(indentation.tabSize);
+
+  const values = await getValues(token, keyToken, parent, valueProviderConfig, workflowContext, indentString);
   let replaceRange: Range | undefined;
   if (token?.range) {
     replaceRange = mapRange(token.range);
   }
 
   return values.map(value => {
+    const newText = value.insertText || value.label;
+
     const item: CompletionItem = {
       label: value.label,
       detail: value.description,
       tags: value.deprecated ? [CompletionItemTag.Deprecated] : undefined,
-      textEdit: replaceRange ? TextEdit.replace(replaceRange, value.label) : undefined
+      textEdit: replaceRange ? TextEdit.replace(replaceRange, newText) : TextEdit.insert(position, newText)
     };
 
     return item;
@@ -117,7 +123,8 @@ async function getValues(
   keyToken: TemplateToken | null,
   parent: TemplateToken | null,
   valueProviderConfig: ValueProviderConfig | undefined,
-  workflowContext: WorkflowContext
+  workflowContext: WorkflowContext,
+  indentation: string
 ): Promise<Value[]> {
   if (!parent) {
     return [];
@@ -150,7 +157,7 @@ async function getValues(
     return [];
   }
 
-  const values = definitionValues(def);
+  const values = definitionValues(def, indentation);
   return filterAndSortCompletionOptions(values, existingValues);
 }
 
diff --git a/actions-languageservice/src/utils/indentation-guesser.ts b/actions-languageservice/src/utils/indentation-guesser.ts
new file mode 100644
index 0000000..4f527a9
--- /dev/null
+++ b/actions-languageservice/src/utils/indentation-guesser.ts
@@ -0,0 +1,269 @@
+// Copied from https://github.com/microsoft/vscode/blob/c3b617f9b058e01cbc5cf00ec3813a7047326503/src/vs/editor/common/model/indentationGuesser.ts
+// And adapted to work with languageserver-textdocument types
+
+import {TextDocument} from "vscode-languageserver-textdocument";
+
+enum CharCode {
+  Space = 32,
+  Tab = 9,
+  Comma = 44
+}
+
+function getLineContent(doc: TextDocument, lineNumber: number): string {
+  return doc.getText({
+    start: {
+      line: lineNumber - 1,
+      character: 0
+    },
+    end: {
+      line: lineNumber - 1,
+      character: Number.MAX_SAFE_INTEGER
+    }
+  });
+}
+
+function getLineCharCode(doc: TextDocument, lineNumber: number, index: number): number {
+  return doc
+    .getText({
+      start: {
+        line: lineNumber - 1,
+        character: index
+      },
+      end: {
+        line: lineNumber - 1,
+        character: index + 1
+      }
+    })
+    .charCodeAt(0);
+}
+
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+class SpacesDiffResult {
+  public spacesDiff: number = 0;
+  public looksLikeAlignment: boolean = false;
+}
+
+/**
+ * Compute the diff in spaces between two line's indentation.
+ */
+function spacesDiff(a: string, aLength: number, b: string, bLength: number, result: SpacesDiffResult): void {
+  result.spacesDiff = 0;
+  result.looksLikeAlignment = false;
+
+  // This can go both ways (e.g.):
+  //  - a: "\t"
+  //  - b: "\t    "
+  //  => This should count 1 tab and 4 spaces
+
+  let i: number;
+
+  for (i = 0; i < aLength && i < bLength; i++) {
+    const aCharCode = a.charCodeAt(i);
+    const bCharCode = b.charCodeAt(i);
+
+    if (aCharCode !== bCharCode) {
+      break;
+    }
+  }
+
+  let aSpacesCnt = 0,
+    aTabsCount = 0;
+  for (let j = i; j < aLength; j++) {
+    const aCharCode = a.charCodeAt(j);
+    if (aCharCode === CharCode.Space) {
+      aSpacesCnt++;
+    } else {
+      aTabsCount++;
+    }
+  }
+
+  let bSpacesCnt = 0,
+    bTabsCount = 0;
+  for (let j = i; j < bLength; j++) {
+    const bCharCode = b.charCodeAt(j);
+    if (bCharCode === CharCode.Space) {
+      bSpacesCnt++;
+    } else {
+      bTabsCount++;
+    }
+  }
+
+  if (aSpacesCnt > 0 && aTabsCount > 0) {
+    return;
+  }
+  if (bSpacesCnt > 0 && bTabsCount > 0) {
+    return;
+  }
+
+  const tabsDiff = Math.abs(aTabsCount - bTabsCount);
+  const spacesDiff = Math.abs(aSpacesCnt - bSpacesCnt);
+
+  if (tabsDiff === 0) {
+    // check if the indentation difference might be caused by alignment reasons
+    // sometime folks like to align their code, but this should not be used as a hint
+    result.spacesDiff = spacesDiff;
+
+    if (spacesDiff > 0 && 0 <= bSpacesCnt - 1 && bSpacesCnt - 1 < a.length && bSpacesCnt < b.length) {
+      if (b.charCodeAt(bSpacesCnt) !== CharCode.Space && a.charCodeAt(bSpacesCnt - 1) === CharCode.Space) {
+        if (a.charCodeAt(a.length - 1) === CharCode.Comma) {
+          // This looks like an alignment desire: e.g.
+          // const a = b + c,
+          //       d = b - c;
+          result.looksLikeAlignment = true;
+        }
+      }
+    }
+    return;
+  }
+  if (spacesDiff % tabsDiff === 0) {
+    result.spacesDiff = spacesDiff / tabsDiff;
+    return;
+  }
+}
+
+/**
+ * Result for a guessIndentation
+ */
+export interface IGuessedIndentation {
+  /**
+   * If indentation is based on spaces (`insertSpaces` = true), then what is the number of spaces that make an indent?
+   */
+  tabSize: number;
+  /**
+   * Is indentation based on spaces?
+   */
+  insertSpaces: boolean;
+}
+
+export function guessIndentation(
+  source: TextDocument,
+  defaultTabSize: number,
+  defaultInsertSpaces: boolean
+): IGuessedIndentation {
+  // Look at most at the first 10k lines
+  const linesCount = Math.min(source.lineCount, 10000);
+
+  let linesIndentedWithTabsCount = 0; // number of lines that contain at least one tab in indentation
+  let linesIndentedWithSpacesCount = 0; // number of lines that contain only spaces in indentation
+
+  let previousLineText = ""; // content of latest line that contained non-whitespace chars
+  let previousLineIndentation = 0; // index at which latest line contained the first non-whitespace char
+
+  const ALLOWED_TAB_SIZE_GUESSES = [2, 4, 6, 8, 3, 5, 7]; // prefer even guesses for `tabSize`, limit to [2, 8].
+  const MAX_ALLOWED_TAB_SIZE_GUESS = 8; // max(ALLOWED_TAB_SIZE_GUESSES) = 8
+
+  const spacesDiffCount = [0, 0, 0, 0, 0, 0, 0, 0, 0]; // `tabSize` scores
+  const tmp = new SpacesDiffResult();
+
+  for (let lineNumber = 1; lineNumber <= linesCount; lineNumber++) {
+    const currentLineText = getLineContent(source, lineNumber);
+    const currentLineLength = currentLineText.length;
+
+    // if the text buffer is chunk based, so long lines are cons-string, v8 will flattern the string when we check charCode.
+    // checking charCode on chunks directly is cheaper.
+    const useCurrentLineText = currentLineLength <= 65536;
+
+    let currentLineHasContent = false; // does `currentLineText` contain non-whitespace chars
+    let currentLineIndentation = 0; // index at which `currentLineText` contains the first non-whitespace char
+    let currentLineSpacesCount = 0; // count of spaces found in `currentLineText` indentation
+    let currentLineTabsCount = 0; // count of tabs found in `currentLineText` indentation
+    for (let j = 0, lenJ = currentLineLength; j < lenJ; j++) {
+      const charCode = useCurrentLineText ? currentLineText.charCodeAt(j) : getLineCharCode(source, lineNumber, j);
+
+      if (charCode === CharCode.Tab) {
+        currentLineTabsCount++;
+      } else if (charCode === CharCode.Space) {
+        currentLineSpacesCount++;
+      } else {
+        // Hit non whitespace character on this line
+        currentLineHasContent = true;
+        currentLineIndentation = j;
+        break;
+      }
+    }
+
+    // Ignore empty or only whitespace lines
+    if (!currentLineHasContent) {
+      continue;
+    }
+
+    if (currentLineTabsCount > 0) {
+      linesIndentedWithTabsCount++;
+    } else if (currentLineSpacesCount > 1) {
+      linesIndentedWithSpacesCount++;
+    }
+
+    spacesDiff(previousLineText, previousLineIndentation, currentLineText, currentLineIndentation, tmp);
+
+    if (tmp.looksLikeAlignment) {
+      // if defaultInsertSpaces === true && the spaces count == tabSize, we may want to count it as valid indentation
+      //
+      // - item1
+      //   - item2
+      //
+      // otherwise skip this line entirely
+      //
+      // const a = 1,
+      //       b = 2;
+
+      if (!(defaultInsertSpaces && defaultTabSize === tmp.spacesDiff)) {
+        continue;
+      }
+    }
+
+    const currentSpacesDiff = tmp.spacesDiff;
+    if (currentSpacesDiff <= MAX_ALLOWED_TAB_SIZE_GUESS) {
+      spacesDiffCount[currentSpacesDiff]++;
+    }
+
+    previousLineText = currentLineText;
+    previousLineIndentation = currentLineIndentation;
+  }
+
+  let insertSpaces = defaultInsertSpaces;
+  if (linesIndentedWithTabsCount !== linesIndentedWithSpacesCount) {
+    insertSpaces = linesIndentedWithTabsCount < linesIndentedWithSpacesCount;
+  }
+
+  let tabSize = defaultTabSize;
+
+  // Guess tabSize only if inserting spaces...
+  if (insertSpaces) {
+    let tabSizeScore = insertSpaces ? 0 : 0.1 * linesCount;
+
+    // console.log("score threshold: " + tabSizeScore);
+
+    ALLOWED_TAB_SIZE_GUESSES.forEach(possibleTabSize => {
+      const possibleTabSizeScore = spacesDiffCount[possibleTabSize];
+      if (possibleTabSizeScore > tabSizeScore) {
+        tabSizeScore = possibleTabSizeScore;
+        tabSize = possibleTabSize;
+      }
+    });
+
+    // Let a tabSize of 2 win even if it is not the maximum
+    // (only in case 4 was guessed)
+    if (
+      tabSize === 4 &&
+      spacesDiffCount[4] > 0 &&
+      spacesDiffCount[2] > 0 &&
+      spacesDiffCount[2] >= spacesDiffCount[4] / 2
+    ) {
+      tabSize = 2;
+    }
+  }
+
+  // console.log('--------------------------');
+  // console.log('linesIndentedWithTabsCount: ' + linesIndentedWithTabsCount + ', linesIndentedWithSpacesCount: ' + linesIndentedWithSpacesCount);
+  // console.log('spacesDiffCount: ' + spacesDiffCount);
+  // console.log('tabSize: ' + tabSize + ', tabSizeScore: ' + tabSizeScore);
+
+  return {
+    insertSpaces: insertSpaces,
+    tabSize: tabSize
+  };
+}
diff --git a/actions-languageservice/src/value-providers/config.ts b/actions-languageservice/src/value-providers/config.ts
index 725ad4c..9172cc4 100644
--- a/actions-languageservice/src/value-providers/config.ts
+++ b/actions-languageservice/src/value-providers/config.ts
@@ -4,6 +4,7 @@ export interface Value {
   label: string;
   description?: string;
   deprecated?: boolean;
+  insertText?: string;
 }
 
 export enum ValueProviderKind {
diff --git a/actions-languageservice/src/value-providers/definition.ts b/actions-languageservice/src/value-providers/definition.ts
index 81aaf6a..16ca421 100644
--- a/actions-languageservice/src/value-providers/definition.ts
+++ b/actions-languageservice/src/value-providers/definition.ts
@@ -1,5 +1,6 @@
 import {BooleanDefinition} from "@github/actions-workflow-parser/templates/schema/boolean-definition";
 import {Definition} from "@github/actions-workflow-parser/templates/schema/definition";
+import {DefinitionType} from "@github/actions-workflow-parser/templates/schema/definition-type";
 import {MappingDefinition} from "@github/actions-workflow-parser/templates/schema/mapping-definition";
 import {OneOfDefinition} from "@github/actions-workflow-parser/templates/schema/one-of-definition";
 import {SequenceDefinition} from "@github/actions-workflow-parser/templates/schema/sequence-definition";
@@ -8,15 +9,15 @@ import {getWorkflowSchema} from "@github/actions-workflow-parser/workflows/workf
 import {Value} from "./config";
 import {stringsToValues} from "./strings-to-values";
 
-export function definitionValues(def: Definition): Value[] {
+export function definitionValues(def: Definition, indentation: string): Value[] {
   const schema = getWorkflowSchema();
 
   if (def instanceof MappingDefinition) {
-    return mappingValues(def, schema.definitions);
+    return mappingValues(def, schema.definitions, indentation);
   }
 
   if (def instanceof OneOfDefinition) {
-    return oneOfValues(def, schema.definitions);
+    return oneOfValues(def, schema.definitions, indentation);
   }
 
   if (def instanceof BooleanDefinition) {
@@ -35,30 +36,64 @@ export function definitionValues(def: Definition): Value[] {
   if (def instanceof SequenceDefinition) {
     const itemDef = schema.getDefinition(def.itemType);
     if (itemDef) {
-      return definitionValues(itemDef);
+      return definitionValues(itemDef, indentation);
     }
   }
 
   return [];
 }
 
-function mappingValues(mappingDefinition: MappingDefinition, definitions: {[key: string]: Definition}): Value[] {
+function mappingValues(
+  mappingDefinition: MappingDefinition,
+  definitions: {[key: string]: Definition},
+  indentation: string
+): Value[] {
   const properties: Value[] = [];
   for (const [key, value] of Object.entries(mappingDefinition.properties)) {
+    let insertText: string | undefined;
+
     let description: string | undefined;
     if (value.type) {
       const typeDef = definitions[value.type];
       description = typeDef?.description;
+
+      if (typeDef) {
+        switch (typeDef.definitionType) {
+          case DefinitionType.Sequence:
+            insertText = `${key}:\n${indentation}- `;
+            break;
+
+          case DefinitionType.Mapping:
+            insertText = `${key}:\n${indentation}`;
+            break;
+
+          case DefinitionType.OneOf:
+            // No special insertText in this case
+            break;
+
+          default:
+            insertText = `${key}: `;
+        }
+      }
     }
-    properties.push({label: key, description: description});
+
+    properties.push({
+      label: key,
+      description,
+      insertText
+    });
   }
   return properties;
 }
 
-function oneOfValues(oneOfDefinition: OneOfDefinition, definitions: {[key: string]: Definition}): Value[] {
+function oneOfValues(
+  oneOfDefinition: OneOfDefinition,
+  definitions: {[key: string]: Definition},
+  indentation: string
+): Value[] {
   const values: Value[] = [];
   for (const key of oneOfDefinition.oneOf) {
-    values.push(...definitionValues(definitions[key]));
+    values.push(...definitionValues(definitions[key], indentation));
   }
   return distinctValues(values);
 }