api-and-interface-design SKILL.md skillA

api-and-interface-design from jpeetz/agent-skills is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.

mdr add jpeetz/agent-skills/api-and-interface-design@git:20261019.fbfaf1a

Pins git:20261019.fbfaf1a in mdr.lock. Pin the fingerprint instead.

Audit grade

A, 17 of 17 checks passed

Kind

SKILL.md skill

Repository

jpeetz/agent-skills

Path

skills/api-backend/api-and-interface-design/SKILL.md

Versions recorded

1

Latest version

git:20261019.fbfaf1a, committed Oct 19, 2026

Size

9,834 bytes

Repository stars

14

License

none declared

Use this skill when designing APIs, module boundaries, or any public interface. Create stable, well-documented interfaces that are hard to misuse — REST endpoints, GraphQL schemas, module contracts, component props. Covers contract-first design, error semantics, validation boundaries, idempotency, and consistent naming.

Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.

What the file says

# API and Interface Design

## Overview

Design stable, well-documented interfaces that are hard to misuse. Good interfaces make the right thing easy and the wrong thing hard. This applies to REST APIs, GraphQL schemas, module boundaries, component props, and any surface where one piece of code talks to another.

## When to Use

- Designing new API endpoints
- Defining module boundaries or contracts between teams
- Creating component prop interfaces
- Establishing database schema that informs API shape
- Changing existing public interfaces

## Core Principles

### Hyrum's Law

> With a sufficient number of users of an API, all observable behaviors of your system will be depended on by somebody, regardless of what you promise in the contract.

This means: every public behavior — including undocumented quirks, error message text, timing, and ordering — becomes a de facto contract once users depend on it. Design implications:

- **Be intentional about what you expose.** Every observable behavior is a potential commitment.
- **Don't leak implementation details.** If users can observe it, they will depend on it.
…

Read the whole file at its exact version.

How to install

mdr add jpeetz/agent-skills/api-and-interface-design@sha256:e6270095f1d40532

[![mdr](https://markdownregistry.com/badge/art_y6vcrojwlsbztfbp.svg)](https://markdownregistry.com/a/art_y6vcrojwlsbztfbp)

Versions

The registry has recorded 1 version of this file, committed on Oct 19, 2026.

Audit of the latest version

Source

API

GET https://markdownregistry.com/api/v1/artifacts/art_y6vcrojwlsbztfbp
GET https://markdownregistry.com/api/v1/resolve?ref=jpeetz/agent-skills/api-and-interface-design
GET https://markdownregistry.com/api/v1/blob/e6270095f1d40532df8e09c17f90ad25fe0a5a89a3fdbdb9e89eaaabb52e7140

Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.

Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.

More from jpeetz/agent-skills

Every file in jpeetz/agent-skills

Other files named api-and-interface-design

Browse by kind, by grade A, or by owner.