Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
git clone --depth 1 https://github.com/markmhendrickson/foundationWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/rules/markmhendrickson/foundation/native_browser_debugging)<a href="https://agentmods.dev/rules/markmhendrickson/foundation/native_browser_debugging"><img src="https://agentmods.dev/badge/rules/markmhendrickson/foundation/native_browser_debugging/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/rules/markmhendrickson/foundation/native_browser_debugging"><img src="https://agentmods.dev/badge/rules/markmhendrickson/foundation/native_browser_debugging.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00027 | $0.00494 |
| Opus 5.5 | $0.00011 | $0.00198 |
| Sonnet 5.5 | $0.00005 | $0.00099 |
| Haiku 4.5 | $0.00003 | $0.00049 |
Grade A, and why
native_browser_debugging scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
Native Browser Debugging Rule
Purpose
Ensure debugging and verification use the native browser for UI flows.
Trigger Patterns
When investigating or verifying UI issues, OAuth flows, or frontend behavior.
Agent Actions
- Use the native browser tools for reproduction and verification.
- Check browser console for errors when making UI changes:
- Use browser MCP tools (
browser_console_messages) to check for console errors - Verify no
Uncaught SyntaxError,Uncaught TypeError, or missing export errors - Fix all console errors before marking UI changes complete
- Use browser MCP tools (
- Capture runtime evidence in the native browser before claiming resolution.
- Use Playwright only as supplemental coverage, not as the primary confirmation step.
Constraints
- MUST use the native browser to reproduce UI issues when possible.
- MUST use the native browser to confirm fixes for UI flows.
- MUST check browser console for errors when making UI-impacting changes.
- MUST fix all console errors (import/export errors, runtime errors) before marking UI changes complete.
- MUST NOT claim UI fixes without native browser confirmation.
- MUST NOT mark UI changes complete if console errors exist.
Agent Instructions
When to Load This Document
Load when debugging UI flows or confirming UI fixes.
Required Co-Loaded Documents
- Repository documentation standards
Constraints Agents Must Enforce
- Use native browser tooling for UI debugging and verification.
- Collect runtime evidence from the native browser before concluding resolution.
- Check browser console for errors after all UI changes.
- Fix all console errors before marking UI work complete.
Forbidden Patterns
- Declaring UI bugs fixed without native browser verification.
- Relying only on headless tests for UI verification.
- Ignoring console errors in the browser.
- Marking UI changes complete with console errors present.
Validation Checklist
- Native browser used to reproduce the issue
- Native browser used to confirm the fix
- Browser console checked for errors (using
browser_console_messagesMCP tool) - No console errors present (no import/export errors, no runtime errors)
- Runtime evidence captured during reproduction and verification
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 65 lines · 27 tokens per session scan A bac5dc1cddeb
native_browser_debugging is a cursor rule published in the GitHub repository markmhendrickson/foundation (2 stars, last pushed 2mo ago), licensed MIT. It adds 27 tokens to every session and 494 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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mcp-inspector-debugging
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can-decode
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ponytail
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