diff --git a/__tests__/lib/idea-plan-parser.test.ts b/__tests__/lib/idea-plan-parser.test.ts
index 30169aa..c279ea8 100644
--- a/__tests__/lib/idea-plan-parser.test.ts
+++ b/__tests__/lib/idea-plan-parser.test.ts
@@ -62,6 +62,41 @@ body
     }
   })
 
+  it('hints when markdown sneaks into frontmatter', () => {
+    // "1. **...**: [unclosed" triggers a YAMLParseError at the markdown line
+    // (plain-list-with-bold parses as valid YAML without an unclosed flow)
+    const broken = `---
+pbi:
+  title: Test
+  priority: 2
+stories:
+1. **Toggle zichtbaar in productie**: [unclosed
+---
+
+body
+`
+    const r = parsePlanMd(broken)
+    expect(r.ok).toBe(false)
+    if (!r.ok) {
+      expect(r.errors[0].hint).toMatch(/markdown/i)
+      expect(r.errors[0].line).toBeGreaterThan(1)
+    }
+  })
+
+  it('omits hint for non-markdown yaml errors', () => {
+    const broken = `---
+pbi:
+  title: Test
+  priority: [unclosed
+stories:
+  - foo
+---
+`
+    const r = parsePlanMd(broken)
+    expect(r.ok).toBe(false)
+    if (!r.ok) expect(r.errors[0].hint).toBeUndefined()
+  })
+
   it('reports schema-validation error when pbi-section missing', () => {
     const noPbi = `---
 stories:
diff --git a/components/ideas/idea-md-editor.tsx b/components/ideas/idea-md-editor.tsx
index 1d7c46e..85c52bd 100644
--- a/components/ideas/idea-md-editor.tsx
+++ b/components/ideas/idea-md-editor.tsx
@@ -123,6 +123,9 @@ export function IdeaMdEditor({ ideaId, kind, initialValue, onCancel }: Props) {
               <li key={i}>
                 {err.line ? `Regel ${err.line}: ` : ''}
                 {err.message}
+                {err.hint && (
+                  <div className="mt-1 text-foreground/80">Tip: {err.hint}</div>
+                )}
               </li>
             ))}
           </ul>
diff --git a/lib/idea-plan-parser.ts b/lib/idea-plan-parser.ts
index 02b968b..b8202b9 100644
--- a/lib/idea-plan-parser.ts
+++ b/lib/idea-plan-parser.ts
@@ -13,7 +13,7 @@ import {
   type IdeaPlanFrontmatter,
 } from '@/lib/schemas/idea'
 
-export type PlanParseError = { line?: number; message: string }
+export type PlanParseError = { line?: number; message: string; hint?: string }
 
 export type PlanParseResult =
   | { ok: true; plan: IdeaPlanFrontmatter; body: string }
@@ -43,14 +43,23 @@ export function parsePlanMd(md: string): PlanParseResult {
     parsed = parseYaml(frontmatterRaw)
   } catch (err) {
     if (err instanceof YAMLParseError) {
+      const yamlLine = err.linePos?.[0]?.line
+      const fileLine = yamlLine != null ? yamlLine + 1 : undefined
+      const offendingLine =
+        yamlLine != null
+          ? frontmatterRaw.split(/\r?\n/)[(yamlLine ?? 1) - 1]
+          : undefined
+      const isMarkdown =
+        offendingLine != null &&
+        (/^\s*\d+\.\s+\*\*/.test(offendingLine) ||
+          /^\s*[-*]\s+\*\*/.test(offendingLine) ||
+          /^\s*\d+\..*:/.test(offendingLine))
+      const hint = isMarkdown
+        ? 'Lijkt op markdown-content (genummerde of opsommingslijst) binnen YAML-frontmatter. Verplaats deze regels naar na de afsluitende `---`, of zet ze in een `description: |` blok.'
+        : undefined
       return {
         ok: false,
-        errors: [
-          {
-            line: err.linePos?.[0]?.line,
-            message: err.message,
-          },
-        ],
+        errors: [{ line: fileLine, message: err.message, hint }],
       }
     }
     return {