Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add rules/wshobson/agents/020-agent-skill-authoringgit clone --depth 1 https://github.com/wshobson/agentsWhat 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 | $0.00000 | $0.00360 |
| Opus 5 | $0.00000 | $0.00180 |
| Sonnet 5 | $0.00000 | $0.00072 |
| Haiku 4.5 | $0.00000 | $0.00036 |
Grade A, and why
020-agent-skill-authoring 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 2d 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.
What it actually says
Authoring portable plugin content
This content ships to Claude Code, Codex CLI, Cursor, OpenCode, and the Antigravity CLI. The adapter framework handles per-harness mechanics, but content choices affect portability.
Frontmatter
- Agents:
name,description(with "Use when…" trigger),model: opus|sonnet|haiku|inherit, optionaltools:, optionalcolor:. - Skills:
name,description. Other Anthropic SKILL.md fields are optional and respected only on Claude Code. - Commands:
description,argument-hint.
Body
- Use action verbs, not tool-name vocabulary: prefer "open the file" over "use the Read tool". The adapter rewrites a conservative set, but the unrewritten cases bleed through.
- Cap skill body at ~8 KB. Push longer reference material into
skills/<name>/references/files. Codex will hard-truncate at 8 KB anyway. - Don't name agents
default,worker, orexplorer— they collide with Codex built-ins. - Don't reference
TodoWriteas load-bearing — it doesn't exist in Codex, Cursor, or Antigravity. TheTaskspawn tool and hooks don't exist in Codex or Cursor either, but Antigravity supports both through its native equivalents (invoke_subagent/define_subagent, lifecycle hooks).
See docs/authoring.md for the full guide.
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.
- 2d ago First seen · 25 lines · 0 tokens per session scan A d2193416858e
020-agent-skill-authoring is a cursor rule published in the GitHub repository wshobson/agents (39,318 stars, last pushed yesterday), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 360 tokens. 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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