New: 98,000+ skills indexed from GitHub repos with 100+ stars · every skill safety-checkedBrowse top skillsTop skills
Esc to closeBrowse all skills
Submit a skillBrowse skills
Submit a skillBrowse skills

Agent skill

Counterfact Runtime Architecture

by counterfact in counterfact/api-simulator

Safely change Counterfact runtime/server internals while preserving module boundaries, hot reload behavior, and backward compatibility guarantees.

MITAuto-check passedBackend & APIs

Install Counterfact Runtime Architecture

skills CLI
$ npx skills add counterfact/api-simulator --skill counterfact-runtime-architecture -a claude-code

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

GitHub CLI
$ gh skill install counterfact/api-simulator counterfact-runtime-architecture --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/counterfact/api-simulator.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.github/skills/counterfact-runtime-architecture .claude/skills/counterfact-runtime-architecture && 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
counterfact-runtime-architecture
GitHub stars
170
Token cost
~578 tokens
SKILL.md length
162 words
Files
1
Skills in repo
12
Repo updated
First seen
Licence
MIT

At a glance

Safely change Counterfact runtime/server internals while preserving module boundaries, hot reload behavior, and backward compatibility guarantees.

  • Tasks that involve OpenAPI specifications
  • SKILL.md covers When to use this skill, Files to inspect first, Existing conventions to follow and Common mistakes to avoid, plus 1 more section
  • Calls yarn

What it does

Counterfact Runtime Architecture is an agent skill from counterfact/api-simulator. Safely change Counterfact runtime/server internals while preserving module boundaries, hot reload behavior, and backward compatibility guarantees.

Its SKILL.md is about 580 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Backend & APIs, covering OpenAPI specifications. It works with OpenAPI. The repository describes itself as: Turn an OpenAPI spec into a local API in one command. Build and test your frontend with custom responses, shared state, and simulated failures, without waiting for the backend. The licence is MIT.

When your agent uses it

  • Tasks that involve OpenAPI specifications

Example prompts

  • “/counterfact-runtime-architecture”

What it can do on your machine

Read from SKILL.md and the folder at commit 0508aef. 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

    Shell commands in SKILL.md call:

    • yarn

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

  • Network

    No URLs in SKILL.md. Its commands use yarn, which can reach the network depending on how they are called.

    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

Counterfact Runtime Architecture loads about 578 tokens when it runs. Until then it costs about 45 tokens; SKILL.md has 162 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~45
When it runs · the whole SKILL.md, loaded when a task matches
~578

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 counterfact/api-simulator at commit 0508aef, republished under its MIT licence (© counterfact). 162 words, ~578 tokens.

Download SKILL.mdSave it as .claude/skills/counterfact-runtime-architecture/SKILL.md (or your agent's skills folder).
name
counterfact-runtime-architecture
description
Safely change Counterfact runtime/server internals while preserving module boundaries, hot reload behavior, and backward compatibility guarantees.
applyTo
packages/counterfact/src/app.ts, packages/counterfact/src/api-runner.ts, packages/counterfact/src/server/**/*.ts, packages/counterfact/src/util/**/*.ts…

Counterfact Runtime Architecture Skill

When to use this skill

Use this skill when changing runtime orchestration, server dispatch flow, module loading/hot reload, or context/registry behavior.

Files to inspect first

  • packages/counterfact/src/app.ts
  • packages/counterfact/src/api-runner.ts
  • packages/counterfact/src/server/dispatcher.ts
  • packages/counterfact/src/server/module-loader.ts
  • packages/counterfact/src/server/web-server/create-koa-app.ts
  • packages/counterfact/docs/reference.md (architecture + runtime behavior)

Existing conventions to follow

  • Keep orchestration in app.ts / ApiRunner; avoid leaking server details into generator modules.
  • Keep subsystems separated (registry, context-registry, module-loader, dispatcher) and connected through explicit constructor interfaces.
  • Preserve hot-reload expectations: route/module changes should apply without restart and context should survive reloads.
  • Prefer graceful degradation with actionable errors (see docs/development/design-principles.md).

Common mistakes to avoid

  • Coupling generator concerns into packages/counterfact/src/server/* code paths.
  • Breaking prefix/group/version routing derivation in app.ts.
  • Introducing restart-only behavior for changes currently handled by watch/reload paths.
  • Changing response defaults/content negotiation semantics unintentionally in dispatcher or Koa middleware.

How to validate the change

  • Run: yarn lint, yarn build, yarn test.
  • Run focused runtime tests first (for touched areas), e.g. packages/counterfact/test/server/dispatcher.test.ts, packages/counterfact/test/server/module-loader.test.ts, packages/counterfact/test/app.test.ts.
  • Manually sanity-check startup + runtime flow with yarn go:example when behavior changes.

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

Files

Just SKILL.md in .github/skills/counterfact-runtime-architecture of counterfact/api-simulator.

Open the folder on GitHubat commit 0508aef

Compare with similar skills

Counterfact Runtime Architecture 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.

Counterfact Runtime Architecture compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Counterfact Runtime Architecture this skillcounterfact/api-simulator170—~578Automated safety check: PassMIT
ToolJet Marketplace Plugin BuilderToolJet/ToolJet41k—~2.1kAutomated safety check: PassAGPL-3.0
Step Partsearthtojake/text-to-cad19k1 repos~1.5kAutomated safety check: PassMIT
OpenAPI to MCP Servermcp-use/mcp-use11k—~5.2kAutomated safety check: PassApache-2.0
Use Yaakmountain-loop/yaak19k—~1.9kAutomated safety check: PassMIT
API DesignerJeffallan/claude-skills12k1 repos~2kAutomated safety check: PassMIT

Similar skills

  • ToolJet Marketplace Plugin Builder

    ToolJet/ToolJet

    Turns an API description, such as an OpenAPI file or a Postman collection, into a connector plugin for ToolJet's marketplace and checks it with the repo's validator.

    41k GitHub stars~2.1k tokensUpdated today
    Backend & APIsAuto-check passed

  • Step Parts

    earthtojake/text-to-cad

    Find, evaluate, and download common purchasable CAD parts from step.parts, including named off-the-shelf actuators, servos, motors, electronics boards, connectors, screws, bolts, nuts, washers…

    19k GitHub starsUsed in 1 repo~1.5k tokens
    Backend & APIsAuto-check passed

  • OpenAPI to MCP Server

    mcp-use/mcp-use

    Turns an OpenAPI or Swagger spec into an MCP server with the mcp-use TypeScript SDK, mapping each operation to a tool, wiring auth, testing and deploying.

    11k GitHub stars~5.2k tokensUpdated today
    Backend & APIsAuto-check passed

  • Use Yaak

    mountain-loop/yaak

    A skill your agent uses when the user mentions Yaak, a Yaak workspace, or the yaak command, or asks to call, hit, or smoke test HTTP/REST endpoints, save or organize API requests for reuse or manual…

    19k GitHub stars~1.9k tokensUpdated 2 days ago
    Backend & APIsAuto-check passed

  • API Designer

    Jeffallan/claude-skills

    Designs REST and GraphQL APIs from resource modeling to an OpenAPI 3.1 contract, with versioning, pagination and RFC 7807 error handling.

    12k GitHub starsUsed in 1 repo~2k tokens
    Backend & APIsAuto-check passed

  • CLI Creator

    huangruiteng/CS-Notes

    Build a composable CLI for Codex from API docs, an OpenAPI spec, existing curl examples, an SDK, a web app, an admin tool, or a local script.

    4k GitHub starsUsed in 2 repos~2.7k tokens
    Backend & APIsAuto-check passed

More from counterfact/api-simulator

All 12 skills in this repo

  • Counterfact PR Creation

    counterfact/api-simulator

    Create Counterfact pull requests with the required agent-authored acceptance and repository-learning notes; do not use to review another PR.

    170 GitHub stars~918 tokensUpdated today
    Auto-check passed

  • Counterfact Repl

    counterfact/api-simulator

    Interact with Counterfact mock API server programmatically. An agent skill from counterfact/api-simulator.

    170 GitHub stars~3.2k tokensUpdated today
    Auto-check passed

  • Build Simulation

    counterfact/api-simulator

    Build a fully simulated API from an OpenAPI spec using Counterfact.

    170 GitHub stars~2.9k tokensUpdated today
    Auto-check passed

  • Counterfact Maintenance

    counterfact/api-simulator

    Keep contributor changes aligned with repository test patterns, diagnostics, black-box test boundaries, release/versioning workflow, documentation requirements, and compatibility.

    170 GitHub stars~3.1k tokensUpdated today
    Auto-check passed

  • Counterfact Repo Basics

    counterfact/api-simulator

    Provide Counterfact repository orientation, high-level architecture, and the canonical command reference for install/build/test/lint workflows.

    170 GitHub stars~868 tokensUpdated today
    Auto-check passed

  • Route

    counterfact/api-simulator

    Edit Counterfact route files to add endpoint behavior while keeping handlers thin and delegating business logic to context classes.

    170 GitHub stars~341 tokensUpdated today
    Auto-check passed

Works with

Categories

Questions about Counterfact Runtime Architecture

What does Counterfact Runtime Architecture do?

Safely change Counterfact runtime/server internals while preserving module boundaries, hot reload behavior, and backward compatibility guarantees. Counterfact Runtime Architecture is an agent skill from counterfact/api-simulator. Safely change Counterfact runtime/server internals while preserving module boundaries, hot reload behavior, and backward compatibility guarantees.

When should I use Counterfact Runtime Architecture?

Counterfact Runtime Architecture fits situations like: tasks that involve OpenAPI specifications.

How do I install Counterfact Runtime Architecture in Claude Code?

Run `npx skills add counterfact/api-simulator --skill counterfact-runtime-architecture -a claude-code`. Or copy the skill folder (.github/skills/counterfact-runtime-architecture in counterfact/api-simulator) into .claude/skills/counterfact-runtime-architecture in your project. Claude Code loads it when a task matches its description.

How do I install Counterfact Runtime Architecture in Codex?

Run `npx skills add counterfact/api-simulator --skill counterfact-runtime-architecture -a codex`. Or copy the skill folder (.github/skills/counterfact-runtime-architecture in counterfact/api-simulator) into .agents/skills/counterfact-runtime-architecture in your project. Codex loads it when a task matches its description.

Can I use Counterfact Runtime Architecture 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 counterfact/api-simulator --skill counterfact-runtime-architecture -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/counterfact-runtime-architecture, .gemini/skills/counterfact-runtime-architecture, .github/skills/counterfact-runtime-architecture and .opencode/skills/counterfact-runtime-architecture in your project.

What does Counterfact Runtime Architecture need to run?

Going by SKILL.md and its folder, Counterfact Runtime Architecture needs the command-line tools its instructions call (yarn).

Does Counterfact Runtime Architecture 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 Counterfact Runtime Architecture 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 Counterfact Runtime Architecture use?

Counterfact Runtime Architecture 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 Counterfact Runtime Architecture use?

About 578 tokens (SKILL.md is roughly 2.3k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Counterfact Runtime Architecture?

Skills that share tags, products or a category with Counterfact Runtime Architecture: ToolJet Marketplace Plugin Builder (ToolJet/ToolJet, 41k stars), Step Parts (earthtojake/text-to-cad, 19k stars), OpenAPI to MCP Server (mcp-use/mcp-use, 11k stars) and Use Yaak (mountain-loop/yaak, 19k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Counterfact Runtime Architecture?

counterfact (a GitHub organization) maintains it in counterfact/api-simulator, which has 170 GitHub stars. The repository holds 12 skills in this directory. The repository was last updated on October 9, 2026.

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