antithesis-skills: Instructions file for Codex

AGENTS.md

antithesis-skills AGENTS.md is an instructions file for Codex, OpenCode from antithesishq/antithesis-skills. It costs 1,191 tokens per session, scanned A, original, Apache-2.0.

Repository instructions for Antithesis Skills, a collection of AI skills and tools. They explain how skills are organized, how to validate them, which commands run tests, and the required Bash, Python, and naming conventions.

In plain words
What is it for?
Creating skills, validating skill files and changelogs, checking links, running tests, installing the development environment, and following the repository's code conventions.
Why use it?
They provide the rules needed to add or change skills without breaking the repository's checks. This helps catch invalid metadata, missing headings, broken links, style problems, and failing helper tests.

Instructions file for CodexOpenCode

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

This is antithesishq/antithesis-skills's own configuration. It tells Codex and OpenCode how to work on antithesis-skills 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 antithesis-skills configures →

Reuse

Borrowing it

Nothing to install: this file belongs to antithesishq/antithesis-skills. 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/antithesishq/antithesis-skills/main/AGENTS.md
Clone the repo
git clone --depth 1 https://github.com/antithesishq/antithesis-skills

Made for: Codex, OpenCode.

Wrote this? Show the measurements

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<a href="https://agentmods.dev/instructions/antithesishq/antithesis-skills/agents-md"><img src="https://agentmods.dev/badge/instructions/antithesishq/antithesis-skills/agents-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 1,191 This file is loaded in full into every session.
When invoked 1,191 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.01191 $0.01191
Opus 5 $0.00596 $0.00596
Sonnet 5 $0.00238 $0.00238
Haiku 4.5 $0.00119 $0.00119

Measured 10d ago against content hash 88c986a0fd8d, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

antithesis-skills 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 10d 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 · 107 lines

How it starts

The opening of the file, as written. The whole thing — 107 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Repository Guidelines

Project Structure & Module Organization

This repository is organized as a set of AI skills plus validation tooling.

Add new skills as <skill-name>/SKILL.md at the repository root. Keep each skill self-contained in its own directory.

All skills must align with the specification available here: https://agentskills.io/specification.md

Build, Test, and Development Commands

  • make validate: checks each */SKILL.md for YAML frontmatter, a name that matches its directory, a non-TODO description, and at least one top-level # heading. This is the canonical structural check.
  • make validate-changelog: validates CHANGELOG.md format.
  • make validate-links: runs the lychee link checker (config in lychee.toml).
  • make test: runs unit tests for skill helper scripts (process-logs.py in debug; build-url.py in query-logs).
  • make install-dev: bootstraps the dev environment via scripts/install.sh.

Coding Style & Naming Conventions

  • Shell scripts use Bash with strict mode (set -euo pipefail); keep new scripts consistent.
  • Use 2-space indentation in shell blocks to match existing files.
  • Skill directories should use lowercase kebab-case (example: my-new-skill/).
  • SKILL.md must include YAML frontmatter with:
    • name: must exactly match the directory name.
    • description: non-empty, not TODO.
  • Every SKILL.md must include a top-level Markdown heading (# ...).

Python in skill assets must support Python 3.9+

Scripts under */assets/ ship to customers and run against whatever python3 is on their machine (often macOS system Python 3.9). Keep them compatible with Python 3.9.

  • Add from __future__ import annotations at the top so PEP 604 unions (X | None, list[int] | None) and other annotation-only syntax don't evaluate at import time.
  • Do not use Python 3.10+ runtime features: match/case, tomllib, typing.Self, ExceptionGroup / except*, parenthesized with groups.
  • Stick to the standard library — asset scripts must not require pip install on a customer's machine.

Read the full file on GitHub · 107 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. 10d ago First seen · 107 lines · 1,191 tokens per session scan A 88c986a0fd8d

Subscribe to this mod's changes

antithesis-skills AGENTS.md is an instructions file published in the GitHub repository antithesishq/antithesis-skills (267 stars, last pushed yesterday), licensed Apache-2.0. It adds 1,191 tokens to every session, about $0.0060 per session on Opus 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.

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