A guide to building MCP servers, which let language models call tools and read data from outside services. It covers tools, resources, prompts, input checks, errors, and testing.

Use it to create MCP integrations, add callable tools or readable resources, define tool inputs, and troubleshoot server connectivity.

It helps turn an external API or service into a clear, reliable interface that an AI model can use. It also helps diagnose connection and input problems.

mcp-builder — Skill for Kiro by ihatesea69/kiro-kit

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.

Any agent

npx skills add ihatesea69/kiro-kit --skill mcp-builder

Clone the repo

git clone --depth 1 https://github.com/ihatesea69/kiro-kit

Made for: Kiro.

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/ihatesea69/kiro-kit/mcp-builder/github.svg)](https://agentmods.dev/skills/ihatesea69/kiro-kit/mcp-builder)

Your own site

<a href="https://agentmods.dev/skills/ihatesea69/kiro-kit/mcp-builder"><img src="https://agentmods.dev/badge/skills/ihatesea69/kiro-kit/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/ihatesea69/kiro-kit/mcp-builder"><img src="https://agentmods.dev/badge/skills/ihatesea69/kiro-kit/mcp-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 332 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 pass 7 Sept 2026

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.

Model	Per session	Once invoked
Fable 5.1	$0.00032	$0.00332
Opus 5.5	$0.00013	$0.00133
Sonnet 5.5	$0.00006	$0.00066
Haiku 4.5	$0.00003	$0.00033

Measured 1mo ago against content hash ec3158180da0, 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.

The scan reads SKILL.md. This mod also ships 2 executable files (scripts/connections.py, scripts/evaluation.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

.kiro/skills/mcp-builder/SKILL.md · 57 lines

What it actually says

MCP Builder

Activate this skill when building MCP servers to integrate external APIs or services.

When to Use

Creating a new MCP server for an API
Adding tools, prompts, or resources to an MCP server
Debugging MCP server connectivity
Designing tool schemas for LLM consumption

MCP Server Structure

Tools: functions the LLM can call
Resources: data the LLM can read
Prompts: pre-built prompt templates

Implementation (TypeScript)

import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';

const server = new McpServer({ name: 'my-server', version: '1.0.0' });

server.tool('tool-name', { param: z.string() }, async ({ param }) => {
  return { content: [{ type: 'text', text: result }] };
});

Implementation (Python)

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("my-server")

@mcp.tool()
def tool_name(param: str) -> str:
    return result

Rules

Design tools with clear, specific names
Use Zod/Pydantic schemas for input validation
Handle errors gracefully with informative messages
Keep tool descriptions concise but complete
Test tools independently before integration

Files

What ships with it

9 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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.

1mo ago First seen · 57 lines · 32 tokens per session scan A ec3158180da0

Subscribe to this mod's changes

mcp-builder is a skill published in the GitHub repository ihatesea69/kiro-kit (19 stars, last pushed 2mo ago), licensed MIT. It adds 32 tokens to every session and 332 once invoked, about $0.0001 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.

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