api-error-design Skill (samber): Error Responses for a Public API

Makes Claude design the errors your public API returns, so developers can fix problems themselves without opening a ticket.

Installs: 9.4K; on skills.sh
Stars: 9; on GitHub
Files: 5; besides SKILL.md
Updated: Nov 2026; last repo commit

api-error-design makes Claude design the error surface of a public API. It covers a machine-readable error-code taxonomy, the RFC 9457 problem-details format, actionable messages, retryability signals, and documenting every error.

It starts when you mention API error codes, an error taxonomy, RFC 9457, application/problem+json, 4xx/5xx response bodies or confusing error messages. Claude asks 6 opening questions, then works through 6 steps plus a stability contract. The skill bundles no scripts.

Good for

API teams whose failures are a bare 500 with a prose message
Teams adopting RFC 9457 without breaking current integrators
Writers rewriting error messages that cause support tickets

Install api-error-design

Claude Code

Copy this prompt.

Install the api-error-design skill in Claude Code. Run this command:

/plugin marketplace add samber/developer-platform-skills
/plugin install developer-platform-skills@developer-platform-skills

Then check that it loaded and tell me how to use it.

2
Paste it into Claude Code. It shows the change and asks before running it.

Pick one route, not both, or you get every skill twice. The README asks you to install the whole set, not just api-error-design, because the skills reference each other and a lone skill leaves those hand-offs with nowhere to go. The plugin adds all 61 skills in the repo (counted from the repo tree). Its manifests list no hooks, agents or MCP servers.

From the project README. Source.

What's in the skill

When it loads

Design the error surface of a public API so integrators self-serve fixes - a machine-readable error-code taxonomy (flat catalog, code/subcode, Google-style domain/reason), the RFC 9457 problem-details envelope with extension members, actionable error messages, retryability signaling (retryable flag, Retry-After), and per-endpoint error documentation with request-ID tracking. Use whenever the user mentions API error codes, an error taxonomy, RFC 9457, application/problem+json, 4xx/5xx response bodies, or confusing API error messages - even if they never say "error design". Do NOT use for client-side retry mechanics - use samber/developer-platform-skills@api-idempotency-retry - nor for incident and status-page communication - use samber/developer-platform-skills@api-status-communication instead.

Sections in SKILL.md

Clarifying questions
Consumer types
Workflow
1. Audit the error surface
2. Choose the taxonomy
3. Adopt the envelope
4. Rewrite the messages
5. Design the retryability signals
6. Document every error, track every request
Stability contract
Failure modes
Measurement
Invocation examples
References

Key facts

Author: Samuel Berthe
License: MIT
Version: 1.0.2
Installs on skills.sh: 9,401 (Nov 2, 2026)
GitHub stars: 9 (Nov 2, 2026)
skills.sh audits: Gen Agent Trust Hub pass; Socket pass; Snyk pass (Nov 2, 2026)
Last repo commit: Nov 1, 2026
What installs: 6 files including SKILL.md: evals/evals.json and 4 reference files. It bundles no scripts.
Needs: The other skills in the repo; the README says to install the whole set
Works in: Claude Code, Claude.ai, Codex, Cursor, Gemini CLI, and other agents through the skills CLI

What it includes

Asks 6 questions in one batch before designing anything.
Try: “Design an error taxonomy for our public REST API - today every failure is a bare 500 with a prose message.”
Opening questions
Collects real error responses per endpoint and grades them against a failure checklist.
Audit the error surface
Ranks code catalogs: code and subcode, then flat codes, then domain and reason.
Choose the taxonomy
Uses RFC 9457 problem details after picking the right HTTP status.
Adopt the envelope
Names the field, the value received and the constraint broken.
Rewrite the messages
Designs fields that say whether to retry; client backoff stays in api-idempotency-retry.
Design the retryability signals
Lists each status and code in OpenAPI and publishes one catalog page.
Document every error, track every request
Treats error codes as API contract and declares what stays stable.
Stability contract
Advises saving decisions to developer-platform-context.md when memory is a file.
Write · Remember decisions (optional)

From the official docs

Permissions

Low risk

This skill is written advice that bundles no scripts. The one thing it may write is a decisions file, so check what Claude saves.

What it can do

Read your data
Create and change things
Delete things
Read-only mode

Watch out for

It may save decisions to a file
SKILL.md advises using developer-platform-context.md when memory lives in a file, and calls it an advisory reference. Check or delete that file if you do not want decisions kept. github.com
The plugin route adds all 61 skills
The README asks you to install every skill in the repo, and the repo has 61. The plugin manifests list no hooks, agents or MCP servers, and the repo tree holds none. github.com
Folder holds Markdown and one JSON file
This skill's folder has 6 files: SKILL.md, evals/evals.json and 4 reference files. It has no .py, .sh or .js file. github.com

Security advisories

No published security advisories as of Nov 2, 2026.

Technical details

Turning on read-only	No read-only setting is documented. Decline the memory-file suggestion if you want no files written.
Scopes	Asks you opening questions and works from your answers and anything you share, such as specs or docs May save settled decisions to a file named developer-platform-context.md if your memory lives in a file

Questions

How do I install api-error-design?

Use the install box above. The README asks you to install all 61 skills in the repo, not just this one, because the skills point to each other. In Claude Code that is the plugin route, and elsewhere the skills CLI or the client's own route installs the set.

Does api-error-design work in Claude.ai, Codex or Cursor?

The README documents installs for Claude.ai, Claude Code, Codex, Cursor and Gemini CLI. It also lists the skills CLI, which it calls universal for Agent Skills-compatible tools. The Claude.ai route adds the whole repo as a plugin marketplace.

Does it need an API key or any setup?

SKILL.md sets no environment variable and the folder bundles no scripts. It does ask for details of your own API or product in its opening questions.

Is api-error-design safe to use?

The folder holds Markdown and one JSON file, and no scripts. SKILL.md does suggest saving settled decisions to developer-platform-context.md when your memory lives in a file, so check what Claude writes. Our advice: treat the design it produces as a draft for your team to review before you publish it.

api-error-design vs api-idempotency-retry?

This skill owns what the error response signals, including retryability fields. SKILL.md sends client retry mechanics to api-idempotency-retry, and incident or status-page communication to api-status-communication.

Which error format does it recommend?

RFC 9457 problem details, which obsoletes RFC 7807, with the application/problem+json media type. SKILL.md says the HTTP status must still be right first, because proxies, caches and monitors read only the status.

Information

updated Nov 2, 2026

Repository: samber/developer-platform-skills
Folder: skills/api-error-design

samber/developer-platform-skills skills.sh

Sources

Docs, issue trackers and discussions this page is built from.

Show all 6

README · github.com
api-error-design SKILL.md · github.com
api-error-design folder · github.com
api-idempotency-retry SKILL.md · github.com
marketplace.json · github.com
plugin.json · github.com