api-contract-author

A guide for documenting an API contract: the agreed details of how software components communicate through an API.

In plain words
What is it for?
It is for publishing and freezing endpoint contracts under docs/api-contracts, including their format and status.
Why use it?
It gives frontend and backend developers a shared, versioned reference before dependent work begins.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/evolplus/talos/api-contract-author
Any agent
npx skills add evolplus/talos --skill api-contract-author
Clone the repo
git clone --depth 1 https://github.com/evolplus/talos

Made for: Claude Code, Codex.

Per session 48 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,881 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00048 $0.01881
Opus 5 $0.00024 $0.00941
Sonnet 5 $0.00010 $0.00376
Haiku 4.5 $0.00005 $0.00188

Measured 2d ago against content hash 9b060bc34b0e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

api-contract-author 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.

skills/api-contract-author/SKILL.md · 126 lines

How it starts

The opening of the file, as written. The whole thing — 126 lines — stays where its author put it; the contents beside it link to each section on GitHub.

API Contract Author

When to use

You are the BE Dev. Your task introduces or modifies an endpoint that an FE task depends on. CLAUDE.md §10 hard rule: no FE Dev start on a backend-dependent task until the API contract is Frozen. This skill defines the contract format, the freeze discipline, and the versioning policy.

Inputs and outputs

  • Inputs: the SRS requirement(s) the endpoint serves, the architecture decisions that constrain it (auth, observability, error model)
  • Outputs: a contract file under docs/api-contracts/ with Status: Frozen, ready for FE to consume

Format — read from SRS §3.4.4, never decide per task

The kit's format choice is project-wide, declared in docs/SRS.md §3.4.4 API Contract Format. As BE Dev, you do NOT pick the format per task — you read SRS §3.4.4 and use the declared format for the API style your endpoint serves. Mixing formats across endpoints in the same project (e.g., one users.openapi.yaml + one orders.md) is a contract-discipline violation; each API style has a single declared format.

Default formats per API style (from SRS §3.4.4):

API style Default format Acceptable file extensions
REST (sync HTTP) openapi-3.1 .yaml, .yml, .json (with openapi-3.1 tag in info.openapi field)
gRPC proto3 .proto
GraphQL graphql-sdl .graphql, .gql
Async messaging asyncapi-2.x .yaml, .yml, .json (with asyncapi field)
Legacy / prototype only markdown .md — requires ADR justification per SRS §3.4.4

If SRS §3.4.4 declares openapi-3.1 for REST and you're tempted to write endpoint.md because "it's just a prototype," halt and either (a) update the SRS §3.4.4 declaration with an ADR justifying the markdown deviation OR (b) write the contract in the declared OpenAPI format. Don't silently drift.

If SRS §3.4.4 is missing but your task requires an API contract: halt and signal back to the Orchestrator. BA's Phase 1 should have captured the format declaration during ingestion; a missing §3.4.4 indicates an SRS gap that BA must close before BE Dev can proceed. Don't pick a format yourself.

Read the full file on GitHub · 126 lines

Files

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.

Changes

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.

  1. 2d ago First seen · 126 lines · 48 tokens per session scan A 9b060bc34b0e

Subscribe to this mod's changes

api-contract-author is a skill published in the GitHub repository evolplus/talos (8 stars, last pushed 28d ago), licensed Apache-2.0. It adds 48 tokens to every session and 1,881 once invoked, about $0.0002 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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