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Agent skill

API Design

by cbrock84 in cbrock84/headcount

Designs interfaces that survive their consumers — resource modeling, errors, versioning, pagination, and compatibility.

MITAuto-check passedBackend & APIs

Install API Design

skills CLI
$ npx skills add cbrock84/headcount --skill api-design -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install cbrock84/headcount api-design --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/cbrock84/headcount.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/technology/skills/api-design .claude/skills/api-design && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
api-design
GitHub stars
2k
Token cost
~956 tokens
SKILL.md length
523 words
Files
2 (incl. references)
Skills in repo
175
Repo updated
First seen
Licence
MIT

At a glance

Designs interfaces that survive their consumers — resource modeling, errors, versioning, pagination, and compatibility.

  • Tasks that involve API design
  • SKILL.md covers Model the domain, not the…, Errors are part of the contract, Compatibility and Pagination, filtering and limits, plus 3 more sections
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

API Design is an agent skill from cbrock84/headcount. Designs interfaces that survive their consumers — resource modeling, errors, versioning, pagination, and compatibility. Use this to design a new API, review one before it ships, decide how to version or deprecate, fix an interface consumers keep misusing, or work out whether a change is breaking.

Its SKILL.md is about 960 tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files, including reference files (for example `references/sources.md`).

It sits in Backend & APIs, covering API design. The repository describes itself as: An agent organization structured as a company — 15+ departments, 125+ skills, each independently installable, citing the standards and regulators that settle the question. Runs… The licence is MIT.

When your agent uses it

  • Tasks that involve API design

Example prompts

  • “Use the api-design skill to design interfaces that survive their consumers — resource modeling, errors, versioning, pagination, and compatibility”
  • “/api-design”

What it can do on your machine

Read from SKILL.md and the folder at commit 98d1c17. 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.

    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 956 tokens when it runs, and up to ~1.5k if it reads all its reference files. Until then it costs about 77 tokens; SKILL.md has 523 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~77
When it runs · the whole SKILL.md, loaded when a task matches
~956
With references · SKILL.md plus every file in references/, read only if the agent opens them
~1.5k

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

Auto-check passed

The automated check found no risky patterns in SKILL.md.

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 cbrock84/headcount at commit 98d1c17, republished under its MIT licence (© cbrock84). 523 words, ~956 tokens.

Download SKILL.mdSave it as .claude/skills/api-design/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.
name
api-design
description
Designs interfaces that survive their consumers — resource modeling, errors, versioning, pagination, and compatibility. Use this to design a new API, review one before it ships, decide how to version or deprecate, fix an interface consumers keep misusing, or work out whether a change is breaking.

API design

An API is a promise you cannot withdraw once someone depends on it. Design accordingly: the cost of getting it wrong is paid continuously by everyone who integrates.

Model the domain, not the database

Expose concepts the consumer thinks in. An interface that mirrors internal table structure leaks implementation, breaks whenever storage changes, and forces consumers to reconstruct meaning you already had.

Name things as the domain names them. Consistency in naming, casing, date formats and identifier style matters more than any individual choice being optimal — an interface that is uniformly imperfect is learnable, and one that is inconsistently excellent is not.

Errors are part of the contract

Most integrations spend most of their code on failure. Give it the same care as the success path:

  • Distinguish machine-readable code from human-readable message. Consumers branch on the code; the message is for the developer reading logs.
  • Say what to do about it. Retryable or not, and after how long.
  • Never leak internals — stack traces and SQL in error bodies are a security finding as well as bad design.
  • Be consistent about which failures are which status. Validation, authorization, and conflict are different situations and should never share a shape.

Compatibility

Adding an optional field is safe. Removing a field, renaming one, tightening validation, changing a default, or adding a required parameter are all breaking, and the last three break consumers who are doing nothing wrong.

Version when you must break, and be explicit about how long the previous version lives. A deprecation without a date is a deprecation nobody acts on.

Prefer expansion over versioning where possible: a new optional field costs a consumer nothing, a new version costs them a migration.

Show full SKILL.md (240 more words)Show less

Pagination, filtering and limits

Any collection that can grow needs pagination from the first release — retrofitting it is a breaking change to every consumer. Prefer cursors over offsets for anything that changes while being read; offset pagination silently skips and duplicates records under concurrent writes.

State rate limits in the contract and communicate them in responses. An undocumented limit is discovered in the consumer's production incident.

Sources

references/sources.md in this skill lists the outside authorities that settle the questions here — what each one is authoritative for, and what you may do with it. Check them before answering on anything they cover, and cite what you used. Most are free to read and not free to reproduce; the use note on each is binding.

Tooling

Specification and documentation: OpenAPI with Redocly, Stoplight, or Scalar; gRPC with protocol buffers where the consumers are internal services, and similar.

Design review and testing: Postman, Insomnia, Bruno, and similar. Contract testing — Pact and similar — is what catches a breaking change before a consumer does.

Generate the documentation from the specification and the specification from or alongside the code. Hand-maintained API documentation is wrong within a release, and being confidently wrong is worse for a consumer than being absent.

Never

  • Expose internal identifiers or storage structure through the interface.
  • Return errors whose meaning must be inferred from the message text.
  • Tighten validation on an existing endpoint and call it non-breaking.
  • Ship a collection endpoint without pagination.

© cbrock84, 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 (references) in plugins/technology/skills/api-design of cbrock84/headcount.

  • SKILL.md
  • references/sources.md

Open the folder on GitHubat commit 98d1c17

Compare with similar skills

API Design next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

API Design compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
API Design this skillcbrock84/headcount2k—~956Automated safety check: PassMIT
API DesignerJeffallan/claude-skills12k2 repos~2kAutomated safety check: PassMIT
Nodejs Backend Patternsever-works/ever-works15818 repos~4kAutomated safety check: PassAGPL-3.0
Pangolin CRUD Endpointsfosrl/pangolin23k—~461Automated safety check: PassCustom licence
API Design Principlesjh941213/my-cc-harness12620 repos~3.4kAutomated safety check: PassNone
Backend PatternshellangleZ/burn-in-cceverywhere-ralph11217 repos~3.3kAutomated safety check: PassNone

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Categories

Questions about API Design

What does API Design do?

Designs interfaces that survive their consumers — resource modeling, errors, versioning, pagination, and compatibility. API Design is an agent skill from cbrock84/headcount. Designs interfaces that survive their consumers — resource modeling, errors, versioning, pagination, and compatibility.

When should I use API Design?

API Design fits situations like: tasks that involve API design.

How do I install API Design in Claude Code?

Run `npx skills add cbrock84/headcount --skill api-design -a claude-code`. Or copy the skill folder (plugins/technology/skills/api-design in cbrock84/headcount) into .claude/skills/api-design in your project. Claude Code loads it when a task matches its description.

How do I install API Design in Codex?

Run `npx skills add cbrock84/headcount --skill api-design -a codex`. Or copy the skill folder (plugins/technology/skills/api-design in cbrock84/headcount) into .agents/skills/api-design in your project. Codex loads it when a task matches its description.

Can I use API Design in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add cbrock84/headcount --skill api-design -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/api-design, .gemini/skills/api-design, .github/skills/api-design and .opencode/skills/api-design in your project.

What does API Design need to run?

SKILL.md names no scripts, command-line tools or credentials: API Design is instructions for the agent only.

Does API Design access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is API Design safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does API Design use?

API Design is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does API Design use?

About 956 tokens (SKILL.md is roughly 3.8k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 558 tokens, read only when the agent opens those files.

What are the alternatives to API Design?

Skills that share tags, products or a category with API Design: API Designer (Jeffallan/claude-skills, 12k stars), Nodejs Backend Patterns (ever-works/ever-works, 158 stars), Pangolin CRUD Endpoints (fosrl/pangolin, 23k stars) and API Design Principles (jh941213/my-cc-harness, 126 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains API Design?

cbrock84 (a GitHub user) maintains it in cbrock84/headcount, which has 2,007 GitHub stars. The repository holds 175 skills in this directory. The repository was last updated on September 17, 2026.

Source: cbrock84/headcount on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.