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/riekelt/technical-writer/documenting-contractsnpx skills add riekelt/technical-writer --skill documenting-contractsgit clone --depth 1 https://github.com/riekelt/technical-writerWrote 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/riekelt/technical-writer/documenting-contracts)<a href="https://agentmods.dev/skills/riekelt/technical-writer/documenting-contracts"><img src="https://agentmods.dev/badge/skills/riekelt/technical-writer/documenting-contracts.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00107 | $0.01526 |
| Opus 5 | $0.00053 | $0.00763 |
| Sonnet 5 | $0.00021 | $0.00305 |
| Haiku 4.5 | $0.00011 | $0.00153 |
Grade A, and why
documenting-contracts 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 4d 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 — 104 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Documenting contracts
REQUIRED BACKGROUND: the technical-writing skill (hard rules, truth rules, style).
Overview
A contract document is read by a stranger who cannot see the code and is about to depend on it. Core principle: document the wire, exhaustively, with each detail at its own level; the caller's language is the wire format and domain terms, never the implementation's types. Contract surfaces are reference kind, so the core Reference rule applies: every endpoint, every field, every error. An omission here is a hole a caller falls into.
When to invoke, and not
Invoke when documenting anything machines call or parse: REST and RPC endpoints, message queues and topics, webhooks, CLI commands, file formats. The api-reference.md of a legacy campaign (documenting-legacy-codebases) is this skill's document. Do NOT invoke for internal code interfaces, which the code documents itself, or for configuration references, which belong in config-reference.md under the core Reference rule. Judging whether the contract is well designed is out of scope: this skill documents the contract that exists.
One home versus generated specs
When an OpenAPI or AsyncAPI spec exists, or the code generates one, that spec owns the field tables. The markdown then documents only what the spec cannot say (semantics, side effects, ordering, omitted-versus-null) and links the spec; hand-maintaining field tables beside a generated one builds a second home that drifts. The catalog below is for the common legacy case where no machine spec exists, and writing one is not this document's job.
The four detail levels
Most bad contract documents mix these; this template gives each level its own home, and the writer moves detail found at the wrong level into the level that owns it:
| Level | The caller asks | Home |
|---|---|---|
| Index | What exists here | The endpoint, message, and command tables |
| Semantics | What invoking it does | Per-endpoint, per-message, and per-command prose: side effects, events published, idempotency, redelivery, exit behavior, quirks |
| Shape | What crosses the wire | The DTO catalog: one field table per DTO |
| Example | What it looks like | At most one illustrative example per DTO |
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.
- 4d ago First seen · 104 lines · 107 tokens per session scan A 86e5b1b66c01
documenting-contracts is a skill published in the GitHub repository riekelt/technical-writer (15 stars, last pushed 5d ago), licensed MIT. It adds 107 tokens to every session and 1,526 once invoked, about $0.0005 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.
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