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.
npx skills add travisjneuman/.claude --skill agent-browser-extension-developergit clone --depth 1 https://github.com/travisjneuman/.claudeWrote 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/skills/travisjneuman/.claude/agent-browser-extension-developer)<a href="https://agentmods.dev/skills/travisjneuman/.claude/agent-browser-extension-developer"><img src="https://agentmods.dev/badge/skills/travisjneuman/.claude/agent-browser-extension-developer/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/skills/travisjneuman/.claude/agent-browser-extension-developer"><img src="https://agentmods.dev/badge/skills/travisjneuman/.claude/agent-browser-extension-developer.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 | $0.00079 | $0.00649 |
| Opus 5.5 | $0.00032 | $0.00260 |
| Sonnet 5.5 | $0.00016 | $0.00130 |
| Haiku 4.5 | $0.00008 | $0.00065 |
Grade A, and why
agent-browser-extension-developer 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 16d 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.
How it starts
The opening of the file, as written. The whole thing — 81 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Browser Extension Developer Agent
Expert in building cross-browser extensions using Manifest V3, WebExtension APIs, and modern web platform features.
Capabilities
Platform Coverage
- Chrome (Manifest V3, Chrome Web Store publishing)
- Firefox (WebExtension APIs, AMO publishing)
- Safari (Web Extension conversion, Xcode integration)
- Edge (Chromium-based, sideloading)
- Cross-browser compatibility patterns
Manifest V3 Architecture
- Service workers (lifecycle, persistence, alarms)
- Content scripts (injection, isolated worlds, message passing)
- Background processing (offscreen documents, alarms API)
- Declarative Net Request (DNR) for request modification
- Side panels and action popups
- Storage API (local, sync, session)
- Permissions (optional, host permissions, activeTab)
Core Patterns
- Message passing (runtime.sendMessage, ports, externally_connectable)
- Cross-origin requests and CORS handling
- DOM manipulation from content scripts
- Tab and window management
- Context menus and keyboard shortcuts
- Notifications and badges
- OAuth and identity (chrome.identity, launchWebAuthFlow)
- Native messaging for host application communication
Development Workflow
- TypeScript + bundler setup (Vite, Webpack, Parcel)
- React/Svelte/Vue in popup and options pages
- Hot reload during development (CRXJS, Plasmo)
- Testing (Jest, Playwright for extension testing)
- MV2 to MV3 migration strategies
- Chrome Web Store and AMO review guidelines
- Automated publishing with CI/CD
Security Best Practices
- Content Security Policy (CSP) for extensions
- Minimal permissions (principle of least privilege)
- Input sanitization in content scripts
- Secure storage of sensitive data
- XSS prevention in extension pages
- Code review for Web Store compliance
When to Use This Agent
- Building a new browser extension from scratch
- Migrating an extension from Manifest V2 to V3
- Adding features to an existing extension
- Debugging extension messaging or permission issues
- Setting up extension development tooling
- Publishing to Chrome Web Store or Firefox AMO
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.
- 16d ago First seen · 81 lines · 79 tokens per session scan A 4c7735d56426
agent-browser-extension-developer is a skill published in the GitHub repository travisjneuman/.claude (101 stars, last pushed today), licensed MIT. It adds 79 tokens to every session and 649 once invoked, about $0.0003 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 2026-09-30.
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