diff --git a/actions-workflow-parser/src/model/converter/cron.test.ts b/actions-workflow-parser/src/model/converter/cron.test.ts
index 56edded..533350e 100644
--- a/actions-workflow-parser/src/model/converter/cron.test.ts
+++ b/actions-workflow-parser/src/model/converter/cron.test.ts
@@ -3,6 +3,7 @@ import { isValidCron } from "./cron"
 describe("isValidCron", () => {
   const valid = [
     "0 0 * * *",
+    "0 000 001 * *",
     "15 * * * *",
     "2,10 4,5 * * *",
     "30 4-6 * * *",
@@ -19,7 +20,6 @@ describe("isValidCron", () => {
     "0 0 * * SUN-2",
     "0 * * */FEB */TUE",
     "0 2-4/5 * * *",
-    // "0 29/5 * * *" <- crontab guru says this is valid, need to test with go library
   ]
 
   for (const cron of valid) {
@@ -30,13 +30,25 @@ describe("isValidCron", () => {
 
   const invalid = [
     "0 0 * *",
+    "0 0 * * * * *",
+    "0 -1 * * *",
+    "0 1- * * *",
+    "0 /1 * * *",
+    "0 1/ * * *",
+    "0 ,1 * * *",
+    "0 1, * * *",
+    "0 -- * * *",
+    "0 // * * *",
+    "0 ,, * * *",
+    "0 ** * * *",
     "0 0 * * BUN",
     "0 0 * SUN JAN",
     "0 0 * * FRI-TUE",
     "0 12-4 * * *",
     "0 */0 * * *",
-    "0 2/4-5 * * *", // TODO
-    "0 2-4-6/5 * * *", // TODO
+    "0 2/4-5 * * *",
+    "0 2-4-6 * * *",
+    "0 2/4/6 * * *",
   ]
 
   for (const cron of invalid) {
diff --git a/actions-workflow-parser/src/model/converter/cron.ts b/actions-workflow-parser/src/model/converter/cron.ts
index 52b1cab..6875928 100644
--- a/actions-workflow-parser/src/model/converter/cron.ts
+++ b/actions-workflow-parser/src/model/converter/cron.ts
@@ -62,12 +62,15 @@ function validateRange(
     return true
   }
 
+  // Operator precedence: , > / > -
   if (value.includes(",")) {
     if (!allowSeparators) {
       return false
     }
     // Allow separators
-    return value.split(",").every((v) => validateRange(v, range))
+    return value.split(",").every((v) => {
+      v && validateRange(v, range)
+    })
   }
 
   if (value.includes("/")) {
@@ -76,18 +79,24 @@ function validateRange(
     }
 
     const [start, step, ...rest] = value.split("/")
-    // Supports */TUE and similar, which nees to be verified with the go cron library
+    // Supports */TUE and similar, which needs to be verified with the go cron library
     const stepNumber = convertToNumber(range, step)
-    if (rest.length > 0 || stepNumber <= 0) {
+    if (rest.length > 0 || stepNumber <= 0 || !start || !step) {
       return false
     }
     return (
-      validateRange(start, range, false) && validateRange(step, range, false)
+      validateRange(start, range) && validateRange(step, range, false)
     )
   }
 
   if (value.includes("-")) {
-    const [start, end] = value.split("-")
+    if (!allowSeparators) {
+      return false
+    }
+    const [start, end, ...rest] = value.split("-")
+    if (rest.length > 0 || !start || !end) {
+      return false
+    }
 
     // Convert name to integers so we can make sure end >= start
     const startNumber = convertToNumber(range, start)