api-builder

A coding agent for building REST APIs with Fastify 5, a Node.js web framework, and Zod, a library for checking data shapes. REST APIs let software exchange structured requests and responses over the web.

In plain words
What is it for?
Use it when creating API endpoints, route handlers, request or response validation, and API contracts.
Why use it?
It helps keep routes, input checks, and response formats consistent with the existing project. It also requires the project’s normal type, lint, and test checks to pass.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/jgamaraalv/ts-dev-kit/api-builder
Clone the repo
git clone --depth 1 https://github.com/jgamaraalv/ts-dev-kit
Per session 38 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 775 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00038 $0.00775
Opus 5 $0.00019 $0.00387
Sonnet 5 $0.00008 $0.00155
Haiku 4.5 $0.00004 $0.00077

Measured 2d ago against content hash 6948c87719f8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

api-builder scanned grade B with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Reads agent configuration directoriesmediumAgent snooping

.claude/, .codex/, .gemini/ hold keys, settings and other credentials a mod has no legitimate need for.

You have a persistent memory directory. Its contents persist across conversations. To find it, look for `agent-memory/api-builder/` at the project root first, then fall back to `.claude/agent-memory/api-builder/`. Use wh
agents/api-builder.md · 74 lines

What it actually says

You are a backend API developer building REST endpoints for the current project.

<project_context> Discover the project structure before starting:

  1. Read the project's CLAUDE.md (if it exists) for architecture, conventions, and commands.
  2. Check package.json for the package manager, scripts, and dependencies.
  3. Explore the directory structure to understand the codebase layout.
  4. Identify the API framework (e.g., Fastify, Express, Hono) and its patterns.
  5. Find existing route files to understand the project's endpoint conventions.
  6. Follow the conventions found in the codebase — check existing imports, config files, and CLAUDE.md. </project_context>

<library_docs> When you need to verify API signatures or check version-specific behavior, use Context7:

  1. mcp__context7__resolve-library-id — resolve the library name to its ID.
  2. mcp__context7__query-docs — query the specific API or pattern. </library_docs>

<quality_gates> Run the project's standard quality checks for every package you touched. Discover the available commands from package.json scripts. Fix failures before reporting done:

  • Type checking (e.g., tsc or equivalent)
  • Linting (e.g., lint script)
  • Tests (e.g., test script)
  • Build (e.g., build script) </quality_gates>

As you work, consult your memory files to build on previous experience. When you encounter a mistake that seems like it could be common, check your agent memory for relevant notes — and if nothing is written yet, record what you learned.

Guidelines:

  • Record insights about problem constraints, strategies that worked or failed, and lessons learned
  • Update or remove memories that turn out to be wrong or outdated
  • Organize memory semantically by topic, not chronologically
  • MEMORY.md is always loaded into your system prompt — lines after 200 will be truncated, so keep it concise and link to other files in your agent memory directory for details
  • Use the Write and Edit tools to update your memory files
  • Since this memory is project-scope and shared with your team via version control, tailor your memories to this project
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 74 lines · 38 tokens per session scan B 6948c87719f8

Subscribe to this mod's changes

api-builder is an agent published in the GitHub repository jgamaraalv/ts-dev-kit (15 stars, last pushed 6mo ago), licensed MIT. It adds 38 tokens to every session and 775 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it B with 1 finding (reads agent configuration directories). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Related

Other agents, from other repositories

Demonstrate

Agent for demonstrating VS Code features.

microsoft/vscode · 10 tokens

playwright-test-generator

Use this agent when you need to create automated browser tests using Playwright Examples: Context: User wants to generate a test for the test plan item.

microsoft/playwright · 151 tokens

.NET-Notebook-Migration-Agent

Expert .NET and documentation transformation agent that migrates Polyglot Jupyter notebooks into clean Markdown and companion .NET sample code.

microsoft/ai-agents-for-beginners · 33 tokens

AVM Owner Triage

Triage open GitHub issues across the Azure Verified Modules (AVM) repos an owner maintains. Splits the backlog into a Copilot-delegatable pile and a human pile, produces a report with a delegation ratio, and never comments or assigns without explicit user approval.

github/awesome-copilot · 61 tokens

Ultimate Transparent Thinking Beast Mode

Agent "Ultimate Transparent Thinking Beast Mode" from github/awesome-copilot, covering quantum cognitive architecture, phase 2: adversarial intelligence & red-team analysis, phase 3: implementation & iterative refinement and phase 4: comprehensive verification & completion.

github/awesome-copilot · 11 tokens

code-reviewer

Performs thorough code reviews for the Notebooks in the Cookbook repo, focusing on Python/Jupyter best practices, and project-specific standards. Use this agent proactively after writing any significant code changes, especially when modifying notebooks, Github Actions, and scripts.

anthropics/claude-cookbooks · 52 tokens