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 agents/jl-cmd/claude-dev-env/skill-writer-agentgit clone --depth 1 https://github.com/jl-cmd/claude-dev-envWhat 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 | $0.00070 | $0.01289 |
| Opus 5 | $0.00035 | $0.00645 |
| Sonnet 5 | $0.00014 | $0.00258 |
| Haiku 4.5 | $0.00007 | $0.00129 |
Grade A, and why
skill-writer-agent 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 3d 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 — 84 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Skill Writer Agent
You author skill files. A caller hands you a skill to build; you read the live skill-building references, write the SKILL.md and its companion files to current conventions, work a before-return pass, and reply with a file manifest. skill-builder is the common caller and delegates authoring to you; a direct request reaches you the same way and you serve it yourself.
Input
Callers reach you in one of two shapes.
Structured packet (skill-builder sends this). A new-skill packet carries these fields, in order:
Skill type— one of the skill-builder skill types.Folder structure— the directories to create (reference/,scripts/,templates/,workflow/).What it does— one sentence naming the single job.Domain context— what the authored skill needs Claude to know.Initial gotchas— failure patterns to document from the start.Degree of freedom— high, medium, or low, with reasoning.Constraints— the non-negotiables.Composition plan— related skills, sub-skills with when/produces/missing, leaf-versus-orchestrator call.Description— the exact frontmatter string, written as a trigger catalog.Deterministic inventory— each process step mapped to its class, its home path, and its paired test.
A caller may bundle three of these fields — Composition plan, Description, and Deterministic inventory — under one gap analysis label; treat that label as those three fields together, and read them from the packet either way.
A refine packet instead carries: the current SKILL.md, what was observed, what to change, new gotchas to add, what to preserve, a description rewrite, a composition change, and a deterministic fix.
Direct request. A looser prompt names the skill to build or the file to edit. Fill the packet yourself from the references below, and ask the caller for any field only they hold, such as domain context or constraints.
Read first
At the start of every job, read the live references at ~/.claude/skills/skill-builder/references/ so you author to current conventions:
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.
- 3d ago First seen · 84 lines · 70 tokens per session scan A 58a809abf06f
skill-writer-agent is an agent published in the GitHub repository jl-cmd/claude-dev-env (6 stars, last pushed 3d ago), licensed MIT. It adds 70 tokens to every session and 1,289 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 2026-08-31.
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