What is base AGENTS.md?

A set of instructions for AI coding agents working on the Base repository. It explains the project’s working agreement, coding standards, GitHub workflow, and readiness and handoff process.

Use it when making changes in Base or deciding how an agent should work there. It covers pre-edit checks, issue-backed work, design-only sessions, architecture decisions, and the inventory-to-handoff workflow.

It gives agents repository-specific rules and points them to the relevant contributor documentation. This reduces inconsistent changes and keeps project-specific application work in the correct repository.

How basefoundry/base configures Codex and OpenCode

Reuse

Borrowing it

Nothing to install: this file belongs to basefoundry/base. 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/basefoundry/base/main/AGENTS.md

Clone the repo

git clone --depth 1 https://github.com/basefoundry/base

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/basefoundry/base/agents-md/github.svg)](https://agentmods.dev/instructions/basefoundry/base/agents-md)

Your own site

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

Per session 1,086 This file is loaded in full into every session.

When invoked 1,086 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	$0.01086	$0.01086
Opus 5.5	$0.00434	$0.00434
Sonnet 5.5	$0.00217	$0.00217
Haiku 4.5	$0.00109	$0.00109

Measured 2mo ago against content hash 39ab211e1e7f, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

base 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 · 99 lines

How it starts

The opening of the file, as written. The whole thing — 99 lines — stays where its author put it; the contents beside it link to each section on GitHub.

AI Agent Guidance

This file gives coding agents the repository-specific rules for Base. It is a navigation layer over the existing contributor docs, not a replacement for them.

Working Agreement

Follow CONTRIBUTING.md for workflow and STANDARDS.md for code standards.
Keep Base focused as the local operating contract for deterministic readiness and handoff across independent Git repositories. Its durable loop is inventory -> prepare -> verify -> trust -> onboard -> hand off.
Keep project-specific setup, service code, and application behavior in the owning project repository unless Base is explicitly the right shared layer.
Adopt external agent workflow ideas only after translating them into Base-specific guidance. Do not vendor or require a third-party methodology when a smaller Base-native rule is enough.
When the user explicitly says a session is design-only or asks for no code changes, stay in discussion mode and do not edit files.
Surface unresolved product or architecture decisions instead of silently choosing defaults for broad changes.

GitHub Workflow

Before implementation, complete the pre-edit workflow gate and work from the issue-backed worktree. Use the GitHub Workflow for the canonical issue, repo-named Project, branch, worktree, pull request, and cleanup policy, including superseded pull requests. This file adds only the agent-specific repository guidance below.

Repository Release Contract

Repositories that publish versioned artifacts should opt into Base's release standardization with basectl repo configure --release --repo <owner/name>. This adds missing release metadata to base_manifest.yaml and a docs/release-process.md guide without overwriting repository-specific release content. Use basectl repo check --release to verify adoption, and read the generated release guide before preparing a release.

Read the full file on GitHub · 99 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 · 99 lines · 1,086 tokens per session scan A 39ab211e1e7f

Subscribe to this mod's changes

base AGENTS.md is an instructions file published in the GitHub repository basefoundry/base (120 stars, last pushed today), licensed Apache-2.0. It adds 1,086 tokens to every session, about $0.0043 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.

automation bash-scripts bootstrap cli dev-environment developer-tools

base AGENTS.md next to 6 instructions from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
base AGENTS.mdbasefoundry/base	Instructions file	120	today	Apache-2.0	A	1,086	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	today	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

base: Instructions file for Codex