What is Browser4 CLAUDE.md?

Project instructions for Browser4, a browser automation system whose Rust command-line tool sends requests to a Kotlin web service and Chrome-based browser driver.

Understanding Browser4's command path, tool dispatch, batch commands, and end-to-end tests, which test the complete system from request to browser action.

They give an AI coding assistant the project's layout and request flow, so it can work in the right part of the codebase.

How platonai/Browser4 configures Claude Code

About the project

Browser4 is an AI-native browser engine that lets autonomous agents and people control real browsers, extract information from web pages, and automate tasks at scale. It combines browser interaction through a Rust CLI and MCP with deterministic selectors, machine-learning clustering, and language-model extraction. The catalogue entries provide skills and instructions for using Browser4.

platonai/Browser4 · 1,169 stars · on GitHub · browser4.io

Reuse

Borrowing it

Nothing to install: this file belongs to platonai/Browser4. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/platonai/Browser4/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/platonai/Browser4

Made for: Claude Code.

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.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/platonai/browser4/claude-md/github.svg)](https://agentmods.dev/instructions/platonai/browser4/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/platonai/browser4/claude-md"><img src="https://agentmods.dev/badge/instructions/platonai/browser4/claude-md/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.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/platonai/browser4/claude-md"><img src="https://agentmods.dev/badge/instructions/platonai/browser4/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 1,205 This file is loaded in full into every session.

When invoked 1,205 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found 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 5.1	$0.01205	$0.01205
Opus 5.5	$0.00482	$0.00482
Sonnet 5.5	$0.00241	$0.00241
Haiku 4.5	$0.00120	$0.00120

Measured 2mo ago against content hash e23151b01210, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

Browser4 CLAUDE.md 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 2mo 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.

CLAUDE.md · 89 lines

How it starts

The opening of the file, as written. The whole thing — 89 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Browser4 — Project Context for Claude

Architecture

browser4-cli (Rust)  ──MCP over HTTP──▶  browser4-rest (Kotlin/Spring)  ──▶  PulsarWebDriver (Kotlin/CDP)
     ▲                                           │
     │                                           ▼
     └──── e2e tests ────▶  Fixture HTTP server (Rust test harness)

CLI: cli/browser4-cli/ — Rust binary, talks to backend via MCP tool calls
Backend: browser4-rest/ — Spring Boot, MCPToolController dispatches tools
Browser driver: browser4-core/browser4-browser/ — PulsarWebDriver wraps CDP (Chrome DevTools Protocol)
Agent tools: browser4-agentic/ — AgentToolManager maps MCP tool names → PulsarWebDriver methods

Key dispatch chain (CLI → browser)

CLI builds MCP tool call: {tool: "browser_type", arguments: {ref: "#el", text: "hi"}}
Backend MCPToolController.callTool() → dispatchToToolExecutor()
normalizeFrontendToolCall() applies FRONTEND_TOOL_NAME_ALIASES (e.g., browser_type → fill)
DefaultArgumentNormalizer maps ref → selector, strips sessionId, converts snake_case keys
resolveMcpToolCall() → ToolCall("tab", "fill", args)
AgentToolManager.execute() → executor.callFunctionOn(toolCall, driver) → PulsarWebDriver.fill()

Batch commands

Batch commands go through handleCommandBatch() → handleBatchTool() in MCPToolController. The CLI's compile_batch_request() builds step arrays with op: "tool" entries. preFocusSelector is only added for keydown/keyup steps (not fill/type/press).

E2E test structure

Tests live in cli/browser4-cli/tests/e2e/
scenarios/mod.rs — registry of all scenarios with requires_browser4, level, group
scenarios/browser.rs — tests against the real Browser4 backend
scenarios/batch.rs — batch-command tests against the real backend
scenarios/mock_server.rs — tests against MockBrowser4Server (no real backend needed)
Real-backend tests use HTML fixtures from browser4-tests/pulsar-tests-common/src/main/resources/static/b4/
State verification: wait_for_state_or_abort() polls read_interactive_state() which evals state-log.textContent

Read the full file on GitHub · 89 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.

2mo ago First seen · 89 lines · 1,205 tokens per session scan A e23151b01210

Subscribe to this mod's changes

Browser4 CLAUDE.md is an instructions file published in the GitHub repository platonai/Browser4 (1,169 stars, last pushed yesterday), licensed Apache-2.0. It adds 1,205 tokens to every session, about $0.0048 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 2026-08-30.

Browser automation agentic-ai agentic-browser ai-browser browser-agent browser-infra browser-use-agent

vscode buildNext.instructions.md

Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).

microsoft/vscode · 9,715 tokens

Browser4: Instructions file for Claude Code

Borrowing it

Wrote this? Show the measurements

What it costs to keep this loaded

Grade A, and why

Nothing flagged

How it starts

Browser4 — Project Context for Claude

Architecture

Key dispatch chain (CLI → browser)

Batch commands

E2E test structure

What this file has done since we first saw it

Other instructions, from other repositories

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