cmux-browser

cmux-browser is a skill for Claude Code, Codex from DJRHails/dotfiles. It costs 56 tokens per session (1,290 once invoked), scanned A, a copy of cmux-browser, MIT.

A browser-automation skill for the cmux macOS app, which provides browser pages that an agent can control. It can open pages, interact with visible elements, wait for changes, and read page content.

In plain words
What is it for?
Use it to open websites, fill in forms, click buttons, choose options, wait for page loads or state changes, and extract information from cmux browser views.
Why use it?
It gives the agent a defined way to keep track of the current browser page and its elements while navigating. Re-checking the page after changes helps avoid acting on outdated controls.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/djrhails/dotfiles/cmux-browser
Any agent
npx skills add DJRHails/dotfiles --skill cmux-browser
Clone the repo
git clone --depth 1 https://github.com/DJRHails/dotfiles

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for cmux-browser

README.md
[![agentmods](https://agentmods.dev/badge/skills/djrhails/dotfiles/cmux-browser.svg)](https://agentmods.dev/skills/djrhails/dotfiles/cmux-browser)
Your own site
<a href="https://agentmods.dev/skills/djrhails/dotfiles/cmux-browser"><img src="https://agentmods.dev/badge/skills/djrhails/dotfiles/cmux-browser.svg" alt="Measured on agentmods" height="20"></a>
Per session 56 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,290 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 95% copy Near-identical to another mod in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00056 $0.01290
Opus 5 $0.00028 $0.00645
Sonnet 5 $0.00011 $0.00258
Haiku 4.5 $0.00006 $0.00129

Measured 3d ago against content hash 510af36844be, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

cmux-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 3d ago.

The scan reads SKILL.md. This mod also ships 3 executable files (templates/authenticated-session.sh, templates/capture-workflow.sh, templates/form-automation.sh), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

Origin

This is a copy

95% identical to cmux-browser — 2 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

modules/agents/skills/cmux-browser/SKILL.md · 142 lines

How it starts

The opening of the file, as written. The whole thing — 142 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Browser Automation with cmux

Use this skill for browser tasks inside cmux webviews.

Core Workflow

  1. Open or target a browser surface.
  2. Verify navigation with get url before waiting or snapshotting.
  3. Snapshot (--interactive) to get fresh element refs.
  4. Act with refs (click, fill, type, select, press).
  5. Wait for state changes.
  6. Re-snapshot after DOM/navigation changes.
cmux --json browser open https://example.com
# use returned surface ref, for example: surface:7

cmux browser surface:7 get url
cmux browser surface:7 wait --load-state complete --timeout-ms 15000
cmux browser surface:7 snapshot --interactive
cmux browser surface:7 fill e1 "hello"
cmux --json browser surface:7 click e2 --snapshot-after
cmux browser surface:7 snapshot --interactive

Surface Targeting

# identify current context
cmux identify --json

# open routed to a specific topology target
cmux browser open https://example.com --workspace workspace:2 --window window:1 --json

Notes:

  • CLI output defaults to short refs (surface:N, pane:N, workspace:N, window:N).
  • UUIDs are still accepted on input; only request UUID output when needed (--id-format uuids|both).
  • Keep using one surface:N per task unless you intentionally switch.

Wait Support

cmux supports wait patterns similar to agent-browser:

cmux browser <surface> wait --selector "#ready" --timeout-ms 10000
cmux browser <surface> wait --text "Success" --timeout-ms 10000
cmux browser <surface> wait --url-contains "/dashboard" --timeout-ms 10000
cmux browser <surface> wait --load-state complete --timeout-ms 15000
cmux browser <surface> wait --function "document.readyState === 'complete'" --timeout-ms 10000

Common Flows

Form Submit

cmux --json browser open https://example.com/signup
cmux browser surface:7 get url
cmux browser surface:7 wait --load-state complete --timeout-ms 15000
cmux browser surface:7 snapshot --interactive
cmux browser surface:7 fill e1 "Jane Doe"
cmux browser surface:7 fill e2 "[email protected]"
cmux --json browser surface:7 click e3 --snapshot-after
cmux browser surface:7 wait --url-contains "/welcome" --timeout-ms 15000
cmux browser surface:7 snapshot --interactive

Read the full file on GitHub · 142 lines

Changes

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.

  1. 3d ago First seen · 142 lines · 56 tokens per session scan A 510af36844be

Subscribe to this mod's changes

cmux-browser is a skill published in the GitHub repository DJRHails/dotfiles (2 stars, last pushed today), licensed MIT. It adds 56 tokens to every session and 1,290 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 95% identical to cmux-browser, differing in 2 lines, and is treated as a copy.

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