diff --git a/actions-workflow-parser/src/model/converter/cron.test.ts b/actions-workflow-parser/src/model/converter/cron.test.ts
new file mode 100644
index 0000000..6f5839f
--- /dev/null
+++ b/actions-workflow-parser/src/model/converter/cron.test.ts
@@ -0,0 +1,43 @@
+import { isValidCron } from "./cron"
+
+describe("isValidCron", () => {
+  const valid = [
+    "0 0 * * *",
+    "15 * * * *",
+    "2,10 4,5 * * *",
+    "30 4-6 * * *",
+    "20/15 * * * *",
+    "30 5,17 * * *",
+    "30 5 * * 1,3",
+    "30 5 * * 2,4",
+    "28 */4 * * *",
+    "28 5,*/4 * * *",
+    "28 5,*/4,6 * * *",
+    "28 5,*/4,6-8 * * *",
+    "0 0 * * SUN",
+    "0 0 * * SUN-TUE",
+    "0 0 * * SUN-2",
+    "0 * * */FEB */TUE",
+  ]
+
+  for (const cron of valid) {
+    it(`${cron} should be valid`, () => {
+      expect(isValidCron(cron)).toBe(true)
+    })
+  }
+
+  const invalid = [
+    "0 0 * *",
+    "0 0 * * BUN",
+    "0 0 * SUN JAN",
+    "0 0 * * FRI-TUE",
+    "0 12-4 * * *",
+    "0 */0 * * *"
+  ]
+
+  for (const cron of invalid) {
+    it(`${cron} should be invalid`, () => {
+      expect(isValidCron(cron)).toBe(false)
+    })
+  }
+})
\ No newline at end of file
diff --git a/actions-workflow-parser/src/model/converter/cron.ts b/actions-workflow-parser/src/model/converter/cron.ts
index 5af4803..52b1cab 100644
--- a/actions-workflow-parser/src/model/converter/cron.ts
+++ b/actions-workflow-parser/src/model/converter/cron.ts
@@ -1,95 +1,111 @@
 const MONTHS = {
-    jan: 1,
-    feb: 2,
-    mar: 3,
-    apr: 4,
-    may: 5,
-    jun: 6,
-    jul: 7,
-    aug: 8,
-    sep: 9,
-    oct: 10,
-    nov: 11,
-    dec: 12,
+  jan: 1,
+  feb: 2,
+  mar: 3,
+  apr: 4,
+  may: 5,
+  jun: 6,
+  jul: 7,
+  aug: 8,
+  sep: 9,
+  oct: 10,
+  nov: 11,
+  dec: 12,
+}
+
+const DAYS = {
+  sun: 0,
+  mon: 1,
+  tue: 2,
+  wed: 3,
+  thu: 4,
+  fri: 5,
+  sat: 6,
+}
+
+// TODO: make this parseCron
+export function isValidCron(cron: string): boolean {
+  // https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#schedule
+
+  const parts = cron.split(" ")
+  if (parts.length != 5) {
+    return false
   }
-  
-  const DAYS = {
-    sun: 0,
-    mon: 1,
-    tue: 2,
-    wed: 3,
-    thu: 4,
-    fri: 5,
-    sat: 6,
+
+  const [minutes, hours, dom, months, dow] = parts
+
+  return (
+    validateRange(minutes, { min: 0, max: 59 }) &&
+    validateRange(hours, { min: 0, max: 23 }) &&
+    validateRange(dom, { min: 1, max: 31 }) &&
+    validateRange(months, { min: 1, max: 12, names: MONTHS }) &&
+    validateRange(dow, { min: 0, max: 6, names: DAYS })
+  )
+}
+
+type Range = {
+  min: number
+  max: number
+  names?: Record<string, number>
+}
+
+function validateRange(
+  value: string,
+  range: Range,
+  allowSeparators = true
+): boolean {
+  if (range.names && range.names[value.toLowerCase()] !== undefined) {
+    return true
   }
-  
-  // TODO: make this parseCron
-  export function isValidCron(cron: string): boolean {
-    // https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#schedule
-  
-    const parts = cron.split(" ")
-    if (parts.length != 5) {
+
+  if (value === "*") {
+    return true
+  }
+
+  if (value.includes(",")) {
+    if (!allowSeparators) {
+      return false
+    }
+    // Allow separators
+    return value.split(",").every((v) => validateRange(v, range))
+  }
+
+  if (value.includes("/")) {
+    if (!allowSeparators) {
+      return false
+    }
+
+    const [start, step, ...rest] = value.split("/")
+    // Supports */TUE and similar, which nees to be verified with the go cron library
+    const stepNumber = convertToNumber(range, step)
+    if (rest.length > 0 || stepNumber <= 0) {
       return false
     }
-  
-    const [minutes, hours, dom, months, dow] = parts
-  
     return (
-      validateRange(minutes, { min: 0, max: 59 }) &&
-      validateRange(hours, { min: 0, max: 23 }) &&
-      validateRange(dom, { min: 1, max: 31 }) &&
-      validateRange(months, { min: 1, max: 12, names: MONTHS }) &&
-      validateRange(dow, { min: 0, max: 6, names: DAYS })
+      validateRange(start, range, false) && validateRange(step, range, false)
     )
   }
-  
-  type Range = {
-    min: number
-    max: number
-    names?: Record<string, number>
+
+  if (value.includes("-")) {
+    const [start, end] = value.split("-")
+
+    // Convert name to integers so we can make sure end >= start
+    const startNumber = convertToNumber(range, start)
+    const endNumber = convertToNumber(range, end)
+    return (
+      validateRange(start, range, false) && validateRange(end, range, false) && endNumber >= startNumber
+    )
   }
-  
-  function validateRange(
-    value: string,
-    range: Range,
-    allowSeparators = true
-  ): boolean {
-    if (range.names && range.names[value.toLowerCase()] !== undefined) {
-      return true
-    }
-  
-    if (value === "*") {
-      return true
-    }
-  
-    if (value.includes(",")) {
-      if (!allowSeparators) {
-        return false
-      }
-      return value.split(",").every((v) => validateRange(v, range, false))
-    }
-  
-    if (value.includes("/")) {
-      if (!allowSeparators) {
-        return false
-      }
-  
-      const [start, step, ...rest] = value.split("/")
-      if (rest.length > 0) {
-        return false
-      }
-      return (
-        validateRange(start, range, false) && validateRange(step, range, false)
-      )
-    }
-  
-    if (value.includes("-")) {
-      const [start, end] = value.split("-")
-      return (
-        validateRange(start, range, false) && validateRange(end, range, false)
-      )
-    }
-  
-    const number = parseInt(value, 10)
-    return !isNaN(number) && number >= range.min && number <= range.max
-  }
\ No newline at end of file
+
+  const number = +value
+  return !isNaN(number) && number >= range.min && number <= range.max
+}
+
+function convertToNumber(range: Range, value: string): number {
+  if (range.names && range.names[value.toLowerCase()] !== undefined) {
+    return +range.names[value.toLowerCase()]
+  }
+  else {
+    return +value
+  }
+}
\ No newline at end of file