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 instructions/gregorbiswanger/featherspec/specsgit clone --depth 1 https://github.com/GregorBiswanger/featherspecWhat 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 | $0.00087 | $0.00087 |
| Opus 5 | $0.00044 | $0.00044 |
| Sonnet 5 | $0.00017 | $0.00017 |
| Haiku 4.5 | $0.00009 | $0.00009 |
Grade A, and why
featherspec specs.instructions.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 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
Follow .claude/rules/specs.md — read that file now and apply
its rules to the matching files you are working on. It is the single source for these rules;
this loader only points at it and holds none of its own.
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 · 9 lines · 87 tokens per session scan A 3a9c90e1b88e
featherspec specs.instructions.md is an instructions file published in the GitHub repository GregorBiswanger/featherspec (44 stars, last pushed 3d ago), licensed MIT. It adds 87 tokens to every session, about $0.0004 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.
Other instructions, from other repositories
spec-kitty AGENTS.md
AGENTS.md instructions for Priivacy-ai/spec-kitty, covering spec kitty development guidelines, ⚠️ critical: load the project charter first, ⚠️ critical: template source location, ⚠️ critical: use canonical sources, never improvise and ⚠️ critical: git workflow — no direct pushes to origin/main.
spec-kit-copilot AGENTS.md
Instructions for github/spec-kit-copilot, covering what this repository is, core skills plugin, core decisions (do not silently undo) and when revving the core skills plugin.
loadout go.instructions.md
Go Engineering Instructions (CLI + API, framework-agnostic).
loadout shell.instructions.md
Shell Script Engineering Instructions (Bash, CLI wrappers, automation).
specs-driven-development-spring-angular always-on.instructions.md
Always-on guardrails for spec-driven Spring + Angular development.
loadout playwright-typescript.instructions.md
Playwright TypeScript Test Generation Instructions.