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Browser4: Instructions file for Codex

AGENTS.md

Browser4 AGENTS.md is an instructions file for Codex, OpenCode from platonai/Browser4. It costs 6,402 tokens per session, scanned B, original, Apache-2.0.

Repository-specific instructions for Browser4, a browser automation project whose command-line client sends requests through a service to a browser driver. They describe the project structure, request flow, batch commands, and known Chrome DevTools Protocol issues.

In plain words
What is it for?
Use them when developing, debugging, or testing Browser4 code across its Rust command-line client, Kotlin service, browser driver, agent tools, and end-to-end test harness.
Why use it?
They help an agent change the correct layer and follow how a browser command travels through the system. This reduces mistakes caused by misunderstanding the repository's architecture or command names.

Instructions file for CodexOpenCode

Written for Codex and OpenCode: the file is AGENTS.md.

This is platonai/Browser4's own configuration. It tells Codex and OpenCode how to work on Browser4 itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything Browser4 configures →

Needs its repository: it reads a path above its own folder, which exists only inside the repository. The line is cd cli/browser4-cli && cargo run --quiet -- htmlsnapshot query --sql @../../query.sql --result-only > ../../results.json.

not rated 1.2krepo +3 changed 5d ago B scan 6,402 tokens original Apache-2.0
View source ↗ platonai/Browser4 browser4.io
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/AGENTS.md
Clone the repo
git clone --depth 1 https://github.com/platonai/Browser4

Made for: Codex, OpenCode.

Wrote this? Show the measurements

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Per session 6,402 This file is loaded in full into every session.
When invoked 6,402 The same file — it is already loaded in full.
Security scan B 1 finding. 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.06402 $0.06402
Opus 5.5 $0.02561 $0.02561
Sonnet 5.5 $0.01280 $0.01280
Haiku 4.5 $0.00640 $0.00640

Measured 5d ago against content hash 67e7bb3ee3d8, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade B, and why

Browser4 AGENTS.md scanned grade B with 1 finding 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 5d 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.

Asks for rootmediumPrivilege escalation

A mod that escalates privileges can change anything on the machine, not only the project.

| `.ps1` scripts don't run on Linux | `sudo apt-get install -y powershell`, then `pwsh script.ps1` |
AGENTS.md · 434 lines

How it starts

The opening of the file, as written. The whole thing — 434 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Repository Guidelines

Repo: https://github.com/platonai/Browser4

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, MCP tool calls over HTTP
  • Backend: browser4-rest/ — Spring Boot, MCPToolController dispatches tools
  • Browser driver: browser4-core/browser4-browser/ — PulsarWebDriver wraps CDP
  • Agent tools: browser4-agentic/ — AgentToolManager maps MCP tool names → driver methods

Dispatch chain (CLI → browser)

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

Batch commands

handleCommandBatch() → handleBatchTool() in MCPToolController. CLI's compile_batch_request() builds step arrays with op: "tool". preFocusSelector only added for keydown/keyup (not fill/type/press).

Known CDP pitfalls

  • crbug.com/444929150: Input.dispatchMouseEvent type mouseWheel race condition in headless Chrome. Fix: dispatch to {passive: false} wheel listener.
  • Cursor positioning: DOM.focus() + Input.dispatchMouseEvent (click) may leave cursor at 0. Fix: setSelectionRange(99999, 99999) after focus+click.
  • Input.insertText racing: 0ms delay between chars drops input events. Fix: use same inter-char delay as type() via randomDelayMillis("type") (90-240ms).

Read the full file on GitHub · 434 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. 5d ago Changed · +11 lines · +255 tokens per session 67e7bb3ee3d8
  2. 16d ago Changed · +39 tokens per session dcdfafb57fdf
  3. 25d ago Changed · +2 lines · +220 tokens per session afec47df9d1e
  4. 1mo ago Changed · +7 lines · +513 tokens per session b06fbfef78a7
  5. 1mo ago Changed · +8 lines · +247 tokens per session 05de55425272
  6. 1mo ago Changed · +26 lines · +350 tokens per session 5adb69332f02
  7. 2mo ago First seen · 380 lines · 4,778 tokens per session scan B 9d2ad598b116

Subscribe to this mod's changes

Browser4 AGENTS.md is an instructions file published in the GitHub repository platonai/Browser4 (1,169 stars, last pushed yesterday), licensed Apache-2.0. It adds 6,402 tokens to every session, about $0.0256 per session on Opus 5.5. A static security scan graded it B with 1 finding (asks for root). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

agentic-aiagentic-browserai-browserbrowser-agentbrowser-infrabrowser-use-agent
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