Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/FerroxLabs/ijfwnpx agentmods add skills/ferroxlabs/ijfw/ijfw-writing-skillsWrote 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.
[](https://agentmods.dev/skills/ferroxlabs/ijfw/ijfw-writing-skills)<a href="https://agentmods.dev/skills/ferroxlabs/ijfw/ijfw-writing-skills"><img src="https://agentmods.dev/badge/skills/ferroxlabs/ijfw/ijfw-writing-skills/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.
<a href="https://agentmods.dev/skills/ferroxlabs/ijfw/ijfw-writing-skills"><img src="https://agentmods.dev/badge/skills/ferroxlabs/ijfw/ijfw-writing-skills.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 4 findings, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Rogue Agent · line 101 Skill modifies its own code, configuration, or behavior at runtime. Self-modification enables an agent to escalate privileges, disable safety constraints, or install persistent backdoors.Fix: Prevent the skill from modifying its own code, SKILL.md, or configuration files. Treat skill files as read-only at runtime.
- medium Agent Snooping · line 151 Skill enumerates or reads other installed skills. Access to other skills' SKILL.md files or the skills directory reveals prompt instructions, capabilities, and secrets that should be invisible to peer skills.Fix: Remove all code or instructions that list or read other skills' files or directories. Skills should operate independently; cross-skill access is a privilege escalation.
- medium Agent Snooping · line 152 Skill enumerates or reads other installed skills. Access to other skills' SKILL.md files or the skills directory reveals prompt instructions, capabilities, and secrets that should be invisible to peer skills.Fix: Remove all code or instructions that list or read other skills' files or directories. Skills should operate independently; cross-skill access is a privilege escalation.
- medium Agent Snooping · line 152 Skill enumerates or reads other installed skills. Access to other skills' SKILL.md files or the skills directory reveals prompt instructions, capabilities, and secrets that should be invisible to peer skills.Fix: Remove all code or instructions that list or read other skills' files or directories. Skills should operate independently; cross-skill access is a privilege escalation.
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 | $0.00069 | $0.02209 |
| Opus 5 | $0.00034 | $0.01104 |
| Sonnet 5 | $0.00014 | $0.00442 |
| Haiku 4.5 | $0.00007 | $0.00221 |
Grade A, and why
ijfw-writing-skills 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 6d 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.
How it starts
The opening of the file, as written. The whole thing — 154 lines — stays where its author put it; the contents beside it link to each section on GitHub.
IJFW Writing Skills -- author a new skill correctly
A skill is a thin loadable trigger surface. The description: is what Claude reads to decide whether to hot-load the body. Get the description wrong and the skill never fires; get the body wrong and the skill misfires when it does fire. This file teaches you to do both right on the first try.
Iron rule: a skill IS its trigger. If the description does not match the words a user would naturally say, the skill does not exist -- it is documentation no one reads.
1. Discovery -- the description is the trigger surface (CSO)
The description: field is the only thing Claude sees at routing time. Treat it like a search-engine snippet, not like a definition.
Shape: start with "Use when ...", end with Trigger: <verbatim phrases>, /<command-name>.
Forbidden words (enforced by scripts/lint/check-skill-descriptions.sh, case-insensitive whole-word): step, steps, phase, phases, mode, modes, workflow, stage, process, sub-skill, skill-name. These signal "the description summarises the body" and cause Claude to skip the body and follow the description shortcut.
Hard cap: 1024 characters. Aim for under 300.
# BAD -- defines the topic, uses forbidden word "process"
description: "Skill for the code review process. Reviews PRs."
# BAD -- workflow summary, uses "phases" and "steps"
description: "Use when reviewing code -- runs three phases, fifteen steps, two passes."
# GOOD -- triggers only, verbatim phrases, slash-command alias
description: "One-line code review comments. Trigger: review, code review, PR review, /ijfw-review"
# GOOD -- "Use when X" + trigger list
description: "Authoring discipline for new IJFW skills. Use when creating a new skill, writing a skill. Trigger: create a new skill, new skill, /ijfw-writing-skills"
2. Frontmatter -- the loadable contract
Required:
name:-- letters, digits, hyphens only. Must match the directory name. Prefix withijfw-for IJFW skills.description:-- see section 1.
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.
- 6d ago First seen · 154 lines · 69 tokens per session scan A 0ba86bbc1aee
ijfw-writing-skills is a skill published in the GitHub repository FerroxLabs/ijfw (210 stars, last pushed 4d ago), licensed MIT. It adds 69 tokens to every session and 2,209 once invoked, about $0.0003 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 2026-09-05.
Other skills, from other repositories
issue-creation
Trigger: issue creation, bug reports, feature requests, or issue approval. Create and triage GitHub issues from repository evidence.
sdd-tasks
Break an SDD change into implementation tasks. Trigger: orchestrator launches task planning for a change.
work-unit-commits
Plan commits as reviewable work units. Trigger: implementation, commit splitting, chained PRs, or keeping tests and docs with code.
systemic-issue-triage
Trigger: new issue, bug report, triage, backlog, issue flood, community report, root cause, dead-end, blocked user. Attack issues by root class, never one-by-one; fixes must shrink the system, not grow it.
sdd-research
Trigger: SDD research, external evidence, source-backed research. Produce auditable evidence for a selected research lane.
skill-improver
Trigger: improve skills, audit skills, refactor skills, skill quality. Audit and upgrade existing LLM-first skills.