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 agentmods add skills/jtsang4/efficient-coding/dev-browsernpx skills add jtsang4/efficient-coding --skill dev-browsergit clone --depth 1 https://github.com/jtsang4/efficient-codingWhat 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 | $0.00084 | $0.03192 |
| Opus 5 | $0.00042 | $0.01596 |
| Sonnet 5 | $0.00017 | $0.00638 |
| Haiku 4.5 | $0.00008 | $0.00319 |
Grade A, and why
dev-browser 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 yesterday.
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 — 426 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Dev Browser Skill
Browser automation that maintains page state across script executions. Write small, focused scripts to accomplish tasks incrementally. Once you've proven out part of a workflow and there is repeated work to be done, you can write a script to do the repeated work in a single execution.
Choosing Your Approach
- Local/source-available sites: Read the source code first to write selectors directly
- Unknown page layouts: Use
getAISnapshot()to discover elements andselectSnapshotRef()to interact with them - Visual feedback: Take screenshots to see what the user sees
Setup
Two modes available. Ask the user if unclear which to use.
Standalone Mode (Default)
Launches a new Chromium browser for fresh automation sessions.
./skills/dev-browser/server.sh &
Options:
--headless- Run in headless mode (no visible browser window)--stealth- Enable anti-detection mode (default: ON)--no-stealth- Disable stealth mode (use plain browser)--driver [playwright|patchright|auto]- Choose browser driver (default: auto)auto- Auto-install and use patchright, fallback to playwright with patchespatchright- Force use of patchrightplaywright- Use standard playwright
--no-flaresolverr- Disable FlareSolverr auto-start (default: enabled if Docker available)--stop- Stop all dev-browser services and cleanup--help- Show help message
Wait for the Ready message before running scripts.
By default, the server automatically:
- Installs Patchright (if not present) for stealth automation
- Enables stealth mode with browser args and runtime patches
- Starts FlareSolverr Docker container for Cloudflare bypass (requires Docker)
To disable automatic features:
# Disable stealth entirely
./skills/dev-browser/server.sh --no-stealth &
# Disable FlareSolverr auto-start
./skills/dev-browser/server.sh --no-flaresolverr &
# Use plain Playwright without anti-detection
./skills/dev-browser/server.sh --no-stealth --driver playwright &
What ships with it
18 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
- bun.lock 46 KB
- package-lock.json 97 KB
- package.json 719 B
- references/scraping.md 5.2 KB
- scripts/start-relay.ts 677 B runs code
- scripts/start-server.ts 6.0 KB runs code
- server.sh 7.4 KB runs code
- src/anti-detection.ts 14 KB runs code
- src/client.ts 18 KB runs code
- src/flaresolverr.ts 9.0 KB runs code
- src/index.ts 10 KB runs code
- src/relay.ts 21 KB runs code
- src/snapshot/browser-script.ts 37 KB runs code
- src/snapshot/index.ts 562 B runs code
- src/snapshot/inject.ts 578 B runs code
- src/types.ts 2.9 KB runs code
- tsconfig.json 849 B
- vitest.config.ts 283 B runs code
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.
- yesterday First seen · 426 lines · 84 tokens per session scan A 0c9e49f3f605
dev-browser is a skill published in the GitHub repository jtsang4/efficient-coding (2 stars, last pushed 6d ago), licensed MIT. It adds 84 tokens to every session and 3,192 once invoked, about $0.0004 per session on Opus 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.
Other skills, from other repositories
qa-testing
Verify your work by actually operating the app or website you changed, instead of assuming it works. Strongly recommended whenever you build, modify, or debug a web app, website, or desktop GUI app. Drive real browsers with the agent-browser CLI and native desktop apps with the cua-driver CLI. These are installed on…
webapp-testing
Start/reuse a local app, wait for readiness, inspect rendered state/console/network, act from observed selectors, and verify with evidence.
webbrowser
Use the native webbrowser module for web search, browsing, authenticated website interaction, forms, file uploads and downloads, screenshots, and user handoff.
package-release
Prepare, publish, repair, or verify package releases and changelogs. Always use for package/version release, publish, ship, tag, changelog, release notes, registry publication, documentation publication, or GitHub Release work. Distinguish package releases from application deployments before acting.
session-reflect
Analyze a user's pi coding-agent session history for recurring behavior, prompting habits, workflow loops, friction, and preferences. Use when the user asks to inspect or reflect on pi sessions, common behavior patterns, agent/user interaction style, prompting habits, or personal pi workflow quality.
twitter-thread-style
Write or revise X/Twitter developer announcement threads in the user's preferred style. Use for technical launch threads, project announcements, release threads, and threads with code screenshots/snippets.