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.
npx agentmods add instructions/mailtrap/mailtrap-mcp/claude-mdgit clone --depth 1 https://github.com/mailtrap/mailtrap-mcpWrote 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.
[](https://agentmods.dev/instructions/mailtrap/mailtrap-mcp/claude-md)<a href="https://agentmods.dev/instructions/mailtrap/mailtrap-mcp/claude-md"><img src="https://agentmods.dev/badge/instructions/mailtrap/mailtrap-mcp/claude-md.svg" alt="Measured on agentmods" height="20"></a>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 | $0.03467 | $0.03467 |
| Opus 5 | $0.01733 | $0.01733 |
| Sonnet 5 | $0.00693 | $0.00693 |
| Haiku 4.5 | $0.00347 | $0.00347 |
Grade A, and why
mailtrap-mcp CLAUDE.md 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 today.
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.
How it starts
The opening of the file, as written. The whole thing — 235 lines — stays where its author put it; the contents beside it link to each section on GitHub.
CLAUDE.md
This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
Development Commands
Build and Development
npm run build- Compile TypeScript to JavaScript in thedist/directorynpm run dev- Run the MCP server with the MCP Inspector for testingnpm run prepublish- Build the project and make the executable script executable
Code Quality
npm run lint- Run both ESLint and TypeScript checksnpm run lint:eslint- Run ESLint for code style checkingnpm run lint:tsc- Run TypeScript compiler for type checking
Testing
npm test- Run all Jest testsnpm run test:watch- Run tests in watch mode during developmentnpm run test:coverage- Run tests with coverage reporting
Project Architecture
This is an MCP (Model Context Protocol) server that integrates with Mailtrap's email service. The architecture follows a modular pattern:
Core Components
- src/index.ts: Main MCP server entry point that registers all tools and handles the server lifecycle
- src/client.ts: Mailtrap client configuration and initialization
- src/config/index.ts: Server configuration constants
Tool Architecture
All tools follow a consistent pattern in the src/tools/ directory:
- Each tool (or tool group) has its own subdirectory (e.g.,
sendEmail/,templates/,emailLogs/) - Tools export an input schema (JSON Schema–style object for MCP
inputSchema) and a handler function - Template operations are grouped under
templates/with individual files for each CRUD operation - Runtime validation: Handlers may validate input with Zod (see
stats/schema.tsandgetSendingStats.ts). Other tools use TypeScript types and ad-hoc checks; adding Zod validation in handlers is recommended for consistency
Tool Structure Pattern
- Single-tool dirs (e.g.
sendEmail/,stats/):index.ts,schema.ts(orschema.ts+ Zod in handler), implementation file(s),__tests__/ - Multi-tool dirs (e.g.
templates/,sandbox/,emailLogs/):index.ts,schemas/*.ts(one schema per tool), implementation file(s),__tests__/
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.
- today Changed · +16 lines · +178 tokens per session a0b646787a40
- 4d ago First seen · 219 lines · 3,289 tokens per session scan A 828d8f3e9cf7
mailtrap-mcp CLAUDE.md is an instructions file published in the GitHub repository mailtrap/mailtrap-mcp (65 stars, last pushed yesterday), licensed MIT. It adds 3,467 tokens to every session, about $0.0173 per session on Opus 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 2026-08-30.
Other instructions, from other repositories
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
spec-kit AGENTS.md
AGENTS.md instructions for github/spec-kit, covering agents.md, about spec kit and specify, quickstart — add a new integration in 5 steps, integration architecture and integrationmanifest — file tracking.
codex AGENTS.md
AGENTS.md instructions for openai/codex, covering rust/codex-rs, the codex-core crate, code review rules, crate api surface and model visible context.
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, applying the notice (cutover) and fallback chain (never fail the build).
next.js AGENTS.md
Instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.