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mcp-builder

mcp-builder is a skill for Claude Code from softspark/ai-toolkit. It costs 39 tokens per session (2,067 once invoked), scanned A, original, Apache-2.0.

A workflow for building MCP servers, which connect AI clients to external APIs, databases, or internal services.

In plain words
What is it for?
Use it to plan tools, choose a communication method, scaffold a server, connect an API, and test the resulting MCP integration.
Why use it?
It breaks server development into research, implementation, testing, and evaluation so important integration details are not missed.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter. Also seen: mentions Claude Code.

Needs its repository: it runs a file that does not travel with it, so clone the repository first. The line is npx @modelcontextprotocol/inspector node dist/server.js.

Part of the ai-toolkit plugin — 115 skills, 44 agents, 14 hooks shipped together

not rated 180repo +1 yesterday A scan SkillSpector: warn 39 tokens original Apache-2.0

Good fit Use it to plan tools, choose a communication method, scaffold a server, connect an API, and test the resulting MCP integration.

Compare 6 skills from other repositories ↓
View source ↗ softspark/ai-toolkit softspark.eu
Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo
git clone --depth 1 https://github.com/softspark/ai-toolkit
agentmods
npx agentmods add skills/softspark/ai-toolkit/mcp-builder

Made for: Claude Code.

Or install ai-toolkit, the plugin that ships this one along with the rest of its 115 skills, 44 agents, 14 hooks.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for mcp-builder

README.md
[![agentmods](https://agentmods.dev/badge/skills/softspark/ai-toolkit/mcp-builder/github.svg)](https://agentmods.dev/skills/softspark/ai-toolkit/mcp-builder)
Your own site
<a href="https://agentmods.dev/skills/softspark/ai-toolkit/mcp-builder"><img src="https://agentmods.dev/badge/skills/softspark/ai-toolkit/mcp-builder/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for mcp-builder

Your own site · 80×15
<a href="https://agentmods.dev/skills/softspark/ai-toolkit/mcp-builder"><img src="https://agentmods.dev/badge/skills/softspark/ai-toolkit/mcp-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,067 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • medium MCP Rug Pull · line 67
    npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.
    Fix: Pin the version: npx @scope/[email protected]
How audits are shown
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 5.1 $0.00039 $0.02067
Opus 5.5 $0.00016 $0.00827
Sonnet 5.5 $0.00008 $0.00413
Haiku 4.5 $0.00004 $0.00207

Measured 1mo ago against content hash f025ef68205d, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

mcp-builder scanned grade A with 0 findings 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 1mo 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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

app/skills/mcp-builder/SKILL.md · 170 lines

How it starts

The opening of the file, as written. The whole thing — 170 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MCP Builder

$ARGUMENTS

Build a production-grade MCP server following Anthropic's 4-phase methodology.

When to Use

  • Wrapping a third-party REST API as MCP tools
  • Exposing an internal database or service to Claude
  • Creating reusable integrations for the team
  • Migrating a custom tool into the MCP ecosystem

For MCP protocol theory, see mcp-patterns knowledge skill (auto-loaded).

4-Phase Workflow

Phase 1 — Research & Planning

  1. Read the target API's documentation (OpenAPI spec, README, changelog).
  2. Identify the 5-15 most useful operations. Prefer workflow-oriented tools over 1:1 API mirror.
  3. Decide transport: stdio for local dev tools, streamable-http for remote/shared.
  4. Decide language: TypeScript recommended (best SDK), Python acceptable (mcp package).
  5. List required secrets (API keys, tokens) and their env var names.

Output: PLAN.md with tool list, transport choice, auth model.

Phase 2 — Implementation

Scaffold:

my-mcp/
├── package.json         # or pyproject.toml
├── src/
│   ├── server.ts        # entry point
│   ├── client.ts        # API client (axios/httpx)
│   ├── tools/           # one file per tool
│   ├── schemas.ts       # Zod/Pydantic schemas
│   └── errors.ts        # typed errors
├── .env.example
└── README.md

Per tool:

  • Input/output schemas (Zod for TS, Pydantic for Python)
  • Clear name with service prefix (e.g. github_create_issue)
  • Description starts with a verb, mentions trigger keywords
  • Annotations: readOnlyHint, destructiveHint, idempotentHint, openWorldHint
  • Pagination support via cursor or page parameters
  • Focused responses — filter noise, don't dump raw API payloads

Phase 3 — Review & Testing

  • TypeScript: npm run typecheck && npm run lint && npm test
  • Python: ruff check . && mypy --strict src/ && pytest
  • MCP Inspector dry-run: 
    npx @modelcontextprotocol/inspector node dist/server.js
  • Verify each tool's schema validates a real request and rejects malformed input.

Read the full file on GitHub · 170 lines

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. 1mo ago First seen · 170 lines · 39 tokens per session scan A f025ef68205d

Subscribe to this mod's changes

mcp-builder is a skill published in the GitHub repository softspark/ai-toolkit (180 stars, last pushed yesterday), licensed Apache-2.0. It adds 39 tokens to every session and 2,067 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

Building agentsClaude Codeai-agentsai-skillsanthropicclaudecline
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