What is anvil AGENTS.md?

Repository instructions for Anvil, a tool that runs code inside isolated Docker sandboxes. The guide covers setup, tests, supported commands, and default limits such as no network access and a time limit.

Use it when developing or testing Anvil, including checking the environment, running commands in supported languages, starting its web log, or launching its MCP server.

It explains how to verify code safely in a restricted environment and how to check that Docker and the required presets are ready.

How tools-for-agents/anvil configures Codex and OpenCode

Reuse

Borrowing it

Nothing to install: this file belongs to tools-for-agents/anvil. 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/tools-for-agents/anvil/main/AGENTS.md

Clone the repo

git clone --depth 1 https://github.com/tools-for-agents/anvil

Made for: Codex, OpenCode.

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/tools-for-agents/anvil/agents-md/github.svg)](https://agentmods.dev/instructions/tools-for-agents/anvil/agents-md)

Your own site

<a href="https://agentmods.dev/instructions/tools-for-agents/anvil/agents-md"><img src="https://agentmods.dev/badge/instructions/tools-for-agents/anvil/agents-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/tools-for-agents/anvil/agents-md"><img src="https://agentmods.dev/badge/instructions/tools-for-agents/anvil/agents-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 854 This file is loaded in full into every session.

When invoked 854 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	$0.00854	$0.00854
Opus 5.5	$0.00342	$0.00342
Sonnet 5.5	$0.00171	$0.00171
Haiku 4.5	$0.00085	$0.00085

Measured 2mo ago against content hash 8d662f51efa6, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

anvil AGENTS.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.

AGENTS.md · 67 lines

How it starts

The opening of the file, as written. The whole thing — 67 lines — stays where its author put it; the contents beside it link to each section on GitHub.

AGENTS.md — anvil

⚒ A throwaway Docker sandbox for agents. Run code or commands in an isolated, resource-limited, network-off container and get structured results back — so an agent verifies work without touching the host. CLI + web + MCP. Part of tools-for-agents.

Setup

node --version                          # 22+ required. Nothing to install.
docker info                             # Docker must be running — anvil is a shell around it
npm test                                # = node --test (docker-dependent tests skip without it)
node src/cli.js check                   # docker + presets: run this first
node src/cli.js run python 'print(1+1)' # langs: bash, sh, node, javascript, python
node src/cli.js run python -            # read the code from stdin
node src/cli.js sh 'ls -la'             # a shell command in alpine
node src/cli.js serve --port 7930       # the run log (real, but absent from --help)
npm run mcp                             # the MCP server, stdio

Defaults every run inherits: --network none, 512m memory, 1 cpu, caps dropped, 30s timeout.

Zero runtime dependencies, and that is a hard rule. No dependencies in package.json, ever — anvil shells out to docker rather than pulling in a client library. Node 22+ gives you node:sqlite.

Env	For
`ANVIL_DB`	the run log — always redirect this in tests
`ANVIL_PORT`	serve port (default 7930)
`ANVIL_CORTEX_URL`	optional cortex link-up

The rules this repo is built on

1. The sandbox's promises are the product. Network off, memory and CPU capped, a hard timeout, and the container is thrown away. Every one of those is a claim someone will rely on to run code they have not read. If you touch container setup, write the test that proves the promise still holds — a sandbox that usually has the network off is not a sandbox.

2. Only the picture is evidence. Run iris against any UI change and look at the shot. Audit phone,tablet,desktop, both themes, with --hover — the run log's rows raise under the pointer, and the ink did not survive it until someone rendered that state.

Read the full file on GitHub · 67 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 · 67 lines · 854 tokens per session scan A 8d662f51efa6

Subscribe to this mod's changes

anvil AGENTS.md is an instructions file published in the GitHub repository tools-for-agents/anvil (0 stars, last pushed 1mo ago), licensed MIT. It adds 854 tokens to every session, about $0.0034 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.

agents ai-agents code-execution docker mcp sandbox

anvil AGENTS.md next to 6 instructions from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
anvil AGENTS.mdtools-for-agents/anvil	Instructions file	0	1mo ago	MIT	A	854	Codex, OpenCode
vscode buildNext.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	9,719	GitHub Copilot
next.js AGENTS.mdvercel/next.js	Instructions file	143k	yesterday	MIT	A	7,461	Codex, OpenCode
langchain AGENTS.mdlangchain-ai/langchain	Instructions file	149k	yesterday	MIT	A	4,680	Codex, OpenCode
vscode oss-third-party-notices.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	5,516	GitHub Copilot
vscode copilot-instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	3,093	GitHub Copilot
deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness	Instructions file	274k	2d ago	MIT	A	4,313	Codex, OpenCode

anvil: Instructions file for Codex