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 skills/ferrus-dev/ferrus/ferrus-executornpx skills add ferrus-dev/ferrus --skill ferrus-executorgit clone --depth 1 https://github.com/ferrus-dev/ferrusWhat 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 | $0.00021 | $0.00340 |
| Opus 5 | $0.00010 | $0.00170 |
| Sonnet 5 | $0.00004 | $0.00068 |
| Haiku 4.5 | $0.00002 | $0.00034 |
Grade A, and why
ferrus-executor 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 yesterday.
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
Executor Operating Playbook
This file is advisory only. Runtime workflow is defined by the initial prompt and Ferrus MCP tools.
Implementation guidelines
- Prefer minimal, targeted diffs
- Avoid unrelated refactoring
- Preserve existing project patterns unless the task requires otherwise
Code navigation
- Start from entrypoints and public interfaces
- Trace dependencies before changing behavior
- Inspect surrounding code before modifying shared logic
Common pitfalls
- Hidden side effects
- Implicit contracts between modules
- Test coupling and fixture assumptions
- State transitions that depend on tool behavior
Ferrus guidance
- Use Ferrus tools rather than reconstructing state from
.ferrus/ - Use
/checkfreely during development; prefer TDD where it fits the task - Run
/checkagain immediately before the final/submit - Read Ferrus resources when they help clarify task context
- Use the consultation template when escalating technical uncertainty
Submission quality
- Provide a clear summary of what changed
- Include concrete manual verification steps
- Mention limitations or follow-up work explicitly when relevant
Useful Ferrus tools
/wait_for_task/check/consult/wait_for_consult/ask_human/wait_for_answer/submit
Useful Ferrus resources
ferrus://taskferrus://reviewferrus://consult_templateferrus://questionferrus://answer
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- yesterday First seen · 61 lines · 21 tokens per session scan A f409b8c7f2d8
ferrus-executor is a skill published in the GitHub repository ferrus-dev/ferrus (2 stars, last pushed 2d ago), licensed Apache-2.0. It adds 21 tokens to every session and 340 once invoked, about $0.0001 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 2026-08-31.
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