A browser-automation guide for navigating websites, interacting with forms and controls, collecting page data, and taking screenshots.

Automating website workflows, testing web apps, extracting information, filling forms, and capturing visual evidence.

It helps developers test or inspect web pages through realistic browser actions while keeping the page state between steps.

dev-browser — Skill by marchatton

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/marchatton/agent-skills/dev-browser

Any agent

npx skills add marchatton/agent-skills --skill dev-browser

Clone the repo

git clone --depth 1 https://github.com/marchatton/agent-skills

Made for: Claude Code, Codex.

Per session 84 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,688 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin 94% 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.

Model	Per session	Once invoked
Fable 5	$0.00084	$0.01688
Opus 5	$0.00042	$0.00844
Sonnet 5	$0.00017	$0.00338
Haiku 4.5	$0.00008	$0.00169

Measured 2d ago against content hash 27f16957d4f7, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

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 2d ago.

The scan reads SKILL.md. This mod also ships 12 executable files (scripts/start-relay.ts, scripts/start-server.ts, server.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

94% identical to dev-browser — 13 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.

.agents/skills/00-utilities/dev-browser/SKILL.md · 215 lines

How it starts

The opening of the file, as written. The whole thing — 215 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 and selectSnapshotRef() 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.

Run all commands from the installed dev-browser skill directory (folder containing this SKILL.md). In Codex this is typically: $CODEX_HOME/skills/dev-browser/.

Standalone Mode (Default)

Launches a new Chromium browser for fresh automation sessions.

cd "$CODEX_HOME/skills/dev-browser" && ./server.sh &

Add --headless flag if user requests it. Wait for the Ready message before running scripts.

Extension Mode

Connects to user's existing Chrome browser. Use this when:

The user is already logged into sites and wants you to do things behind an authed experience that isn't local dev.
The user asks you to use the extension

Important: The core flow is still the same. You create named pages inside of their browser.

Start the relay server:

cd "$CODEX_HOME/skills/dev-browser" && npm i && npm run start-extension &

Wait for Waiting for extension to connect... followed by Extension connected in the console. To know that a client has connected and the browser is ready to be controlled. Workflow:

Scripts call client.page("name") just like the normal mode to create new pages / connect to existing ones.
Automation runs on the user's actual browser session

If the extension hasn't connected yet, tell the user to launch and activate it. Download link: https://github.com/SawyerHood/dev-browser/releases

Read the full file on GitHub · 215 lines

Files

What ships with it

17 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.

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.

2d ago First seen · 215 lines · 84 tokens per session scan A 27f16957d4f7

Subscribe to this mod's changes

dev-browser is a skill published in the GitHub repository marchatton/agent-skills (5 stars, last pushed 5mo ago), licensed MIT. It adds 84 tokens to every session and 1,688 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. It is 94% identical to dev-browser, differing in 13 lines, and is treated as a copy.

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