API Design

What it does

When your agent uses it

• Reviewing an HTTP API — endpoints
• Request and response shapes

Example prompts

• “endpoint”
• “status code”
• “pagination”
• “/api-design”

Workflow steps

8 steps, taken from the first numbered list in SKILL.md.

1. 1Read the existing API first: a neighbouring endpoint, the error helper, the
2. 2Authorize every request against the specific object, not just "is logged
3. 3Validate input at the edge with a schema; reject unknown or malformed fields
4. 4Use status codes for what they mean, and never return 200 with an error body.
5. 5One error shape across the API. Without an existing convention, use RFC 9457
6. 6Additive changes only within a version. Removing or renaming a field,
7. 7Make retries safe: GET, PUT, and DELETE are idempotent; accept an
8. 8Credentials go in headers, never in URLs or query strings.

What it can do on your machine

Read from SKILL.md and the folder at commit ec76a20. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are http).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

API Design loads about 1.3k tokens when it runs. Until then it costs about 87 tokens; SKILL.md has 590 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~87

When it runs · the whole SKILL.md, loaded when a task matches

~1.3k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from WrongStack/WrongStack at commit ec76a20, republished under its MIT licence (© WrongStack). 590 words, ~1,304 tokens.

name

api-design

description

Use this skill when designing, implementing, or reviewing an HTTP API — endpoints, request and response shapes, errors, pagination, versioning, and authorization. Triggers: user says "API", "endpoint", "REST", "route", "status code", "pagination", "request body", "response shape", "OpenAPI", "versioning", "idempotency", "rate limit".

version

2.0.0

required-capabilities

filesystem.read

optional-capabilities

filesystem.write, verification.run

POST /v1/orders
Idempotency-Key: 5c1f…
Content-Type: application/json

{ "items": [{ "sku": "A-100", "qty": 2 }] }

201 Created
Location: /v1/orders/ord_81f2
{ "id": "ord_81f2", "status": "pending", "items": [...], "createdAt": "2026-09-15T10:00:00Z" }

422 Unprocessable Content
Content-Type: application/problem+json

{
  "type": "https://example.com/problems/validation",
  "title": "Invalid order",
  "status": 422,
  "errors": [{ "field": "items[0].qty", "message": "must be at least 1" }]
}

© WrongStack, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 1 other file in packages/core/skills/api-design of WrongStack/WrongStack.

• SKILL.md
• SKILL.save.md

Open the folder on GitHubat commit ec76a20