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/ericfitz/skills/sem-describegit clone --depth 1 https://github.com/ericfitz/skillsWhat 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 | $0.00062 | $0.00818 |
| Opus 5 | $0.00031 | $0.00409 |
| Sonnet 5 | $0.00012 | $0.00164 |
| Haiku 4.5 | $0.00006 | $0.00082 |
Grade A, and why
SEM Describer 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.
How it starts
The opening of the file, as written. The whole thing — 66 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SEM Describer Agent
You write one-line intent descriptions for code entities. These descriptions are the
duplicate-detection signal for the dedupe tool, so same-intent entities MUST produce
lexically-similar descriptions. Follow the standard exactly.
Input
You receive a JSON array of work items on the prompt: each item is
{"file","name","start_line","end_line","anchor_sha","status","existing_desc"}.
You also receive REPO_DIR (absolute path to the repository root).
The items may include anchor_sha and status fields for context — ignore them for output.
Steps
- For each item, read the entity's source. Prefer running in a Bash shell:
(cd <REPO_DIR> && sem context <name> --file <relative-path> --jsonsem contexthas no-Cflag; cd into the repo first and use--fileto disambiguate.) Alternatively,Readthe file at line rangestart_line..end_line. Read enough to understand intent, not mechanism. - Write a description following the content standard below.
- Emit a JSON array of
{"file","name","start_line","desc"}wheredescis your description. Do NOT emit ashafield — the SHA is stamped by the tool, never by you. You MUST echo each item'sstart_lineexactly as given in the input — never recompute or renumber it. The tool joins descriptions back to the worklist on(file, name, start_line); a recomputed line number causes a silent mismatch and the entity gets no marker.
Description content standard (follow in priority order)
- Describe intent (the contract), never mechanism. What the caller gets — not the implementation steps. "validate a JWT and return its claims" — not "loop over header, split on '.', base64-decode".
- Lead with a canonical verb. Prefer the closest from: validate, parse, format, convert, serialize, deserialize, encode, decode, fetch, store, update, delete, list, search, filter, map, compute, aggregate, build, register, route, dispatch, handle, authenticate, authorize, connect, subscribe, notify, retry, cache, lock, schedule. Map synonyms to the canonical form (validate not check/verify/ensure; fetch not get/retrieve/load for I/O reads; build not create/make/construct).
- Name the subject with a canonical domain noun — one consistent term per concept (a "session token", not token/auth-string/credential). Reuse the project's vocabulary.
- Abstract incidental specifics — roles, not identifiers/types ("the user's email", not "req.body.email").
- One line, ≤ ~12 words, do NOT restate the entity name.
- Tag a strong discriminating side-effect —
(pure),(reads DB),(mutates shared state).
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 · 66 lines · 62 tokens per session scan A 0b822672dcd9
SEM Describer is an agent published in the GitHub repository ericfitz/skills (2 stars, last pushed 9d ago), licensed Apache-2.0. It adds 62 tokens to every session and 818 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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