Use when designing or reviewing a public API, exported function signature, module boundary, exported type/interface, or any contract other code depends on.
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
The headline rule, from Scott Meyers (97/55), governs everything else: **make interfaces easy to use correctly and hard to use incorrectly.** Every other decision below is a tactic for that rule — encapsulate behavior so callers can't reach past the contract, lean on the type system so wrong calls fail at compile time.
This is a **rigid** skill. Run the decisions in order. If you can't satisfy one, stop and tell the user what's blocking you.
## When to invoke
Invoke when you're about to:
- Add or change a function/method that will be called from another module, package, service, or repo
- Export a new type, interface, trait, protocol, or class
- Define a request/response schema, RPC method, or message format
- Publish a library, SDK, or plugin contract
- Change an existing public signature (parameter order, optionality, return type, thrown errors)
- Add or remove a configuration flag, CLI option, or env-var contract that other code reads
- Decide what to make `public`, `internal`, `final`, `sealed`, or `private`
- Review an API design, interface, or public contract for usability, correctness, or ergonomics
…
The line at the top of this page pins the label git:20260510.17c5ab8, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
A 17 of 17 checks passed. Fixed automatic checks with no AI involved, so the same checks give the same answer every run.
pass: Frontmatter block present
pass: Frontmatter declares a name
pass: Frontmatter declares a description
pass: Size between 200 bytes and 200 KB (13219 bytes)
pass: No zero-width or bidi control characters
pass: No instruction hidden inside an HTML comment
pass: No link to an exfiltration or paste host
pass: No credential-shaped string
pass: No instruction to send local credentials anywhere
pass: No text hidden with inline styles
pass: No prompt-injection phrasing
pass: No curl or wget piped into a shell
pass: No recursive delete of root, home or parent
pass: No instruction to read or print local credentials
pass: No base64 blob over 200 characters
pass: No link to a raw IP address
pass: No script tag
Source
GitHub
oribarilan/97 · 25 stars · license a license file GitHub does not identify · pushed 2026-10-29 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_vtg4l62qlxilh4xi
GET https://markdownregistry.com/api/v1/resolve?ref=oribarilan/97/api-design
GET https://markdownregistry.com/api/v1/blob/82e85208bb40de63abf3382db0ec2f96a4f2dbbc261b54658e19a6bf1e2eed53
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.
oribarilan/97 · skills/before-you-refactor/SKILL.md · Use when considering, evaluating, or performing a refactor, restructure, cross-file rename, or cleanup
oribarilan/97 · skills/build-deploy-and-tooling/SKILL.md · Use when writing, reviewing, or changing build scripts, CI workflows, deploy pipelines, repo setup, or evaluating a new…
oribarilan/97 · skills/domain-modeling/SKILL.md · Use when introducing, reviewing, or renaming a top-level type, table, or domain concept; or choosing where state lives…
oribarilan/97 · skills/observability/SKILL.md · Use when writing or reviewing request handlers, RPCs, or background jobs for production; adding tracing, metrics, or…
oribarilan/97 · skills/security-and-trust-boundaries/SKILL.md · Use when writing or reviewing code that parses user input, builds SQL/shell commands, handles secrets/credentials…
oribarilan/97 · skills/self-review/SKILL.md · Use when about to commit, finish a task, open a PR, summarize work for the user, or when the user asks for a review or…
oribarilan/97 · skills/testing-discipline/SKILL.md · Use when writing or reviewing tests, designing test data, naming a test, choosing what to assert, or writing test…
oribarilan/97 · skills/working-with-users-and-team/SKILL.md · Use when gathering or interpreting requirements, estimating effort, or communicating with stakeholders/customers about…
affaan-m/ecc · docs/es/skills/api-design/SKILL.md · Patrones de diseño REST API incluyendo nomenclatura de recursos, códigos de estado, paginación, filtrado, respuestas de…
ericrisco/rsc-harness · skills/api-design/SKILL.md · Use when settling the contract of an API you expose, before implementation: resources/URLs, REST vs GraphQL…
yonatangross/orchestkit · plugins/ork/skills/api-design/SKILL.md · API wire contracts for REST and GraphQL: resource shape, versioning and deprecation, RFC 9457 errors, OpenAPI. Use when…
