Form Validation Scan
Find out if your forms accept garbage. No signup required.
Prerequisites
- Playwright MCP (comes with Claude Code)
Trigger
- "Scan my forms for validation gaps"
- "Do my forms validate input?"
- "Form validation audit https://..."
Workflow
- Navigate to the URL using
mcp__playwright__browser_navigate. - Inventory the forms and fields with
mcp__playwright__browser_evaluate:
() => [...document.forms].map(f => ({
id: f.id || f.name || '(unnamed)',
action: f.action,
fields: [...f.elements].filter(e => e.name).map(e => ({
name: e.name, type: e.type, required: e.required,
pattern: e.pattern || null, maxLength: e.maxLength,
})),
}))
- For one representative form, probe behavior with
mcp__playwright__browser_fill_form+mcp__playwright__browser_clickon submit. Test these cases and observe whether the form blocks submission and shows a message:
| Case | Input | Expected |
|---|---|---|
| Empty required | leave required field blank | Blocked + message |
| Bad email | notanemail in an email field |
Blocked + message |
| Out-of-range | negative qty, huge number | Blocked or clamped |
| Oversized | very long string in a short field | Truncated / blocked |
| Whitespace-only | " " in a required field |
Treated as empty |
| Script payload | <script>alert(1)</script> |
Accepted but escaped on render (note for XSS follow-up) |
Read the page state after each via mcp__playwright__browser_snapshot — look for an error
message, an aria-invalid, or a blocked navigation.
- Output:
## Form Validation Scan: [URL]
**Form: "signup" — 3 gaps**
| Field | Required enforced | Format checked | Error shown | Verdict |
|----------|-------------------|----------------|-------------|---------|
| email | yes | NO | no | Accepts "abc" as email |
| password | yes | yes (min 8) | yes | ok |
| age | no | NO | no | Accepts -5 and 9999 |
### Findings
1. `email` — no format validation; `notanemail` submits. Add `type=email` + server check.
2. `age` — accepts negative and absurd values; add `min`/`max` + server validation.
3. Submitting empty `email` shows no inline error — fails silently.
### Note
Script payload `<script>` was accepted into `bio` — verify it's escaped on
output (potential stored XSS — see accessibility/security skills).
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