What is mailosaur-mcp-builder?

A development workflow for building GitHub-ready MCP servers for Mailosaur, an email and messaging testing service. It covers mapping Mailosaur's API or Node.js client into tools that an AI agent can call.

Creating, auditing, extending, and packaging Mailosaur MCP servers with email, SMS, one-time-code, and preview workflows.

It provides checks and conventions for tool design, secrets, destructive actions, downloaded files, and build validation.

mailosaur-mcp-builder — Skill for Codex by MrNewDelhi

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 MrNewDelhi/mailosaur-mcp --skill mailosaur-mcp-builder

Clone the repo

git clone --depth 1 https://github.com/MrNewDelhi/mailosaur-mcp

Made for: Codex.

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/mrnewdelhi/mailosaur-mcp/mailosaur-mcp-builder/github.svg)](https://agentmods.dev/skills/mrnewdelhi/mailosaur-mcp/mailosaur-mcp-builder)

Your own site

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

Per session 79 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 485 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.

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	$0.00079	$0.00485
Opus 5	$0.00039	$0.00243
Sonnet 5	$0.00016	$0.00097
Haiku 4.5	$0.00008	$0.00049

Measured 12d ago against content hash dcb3d863af51, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

mailosaur-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 12d 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.

skills/mailosaur-mcp-builder/SKILL.md · 43 lines

What it actually says

Mailosaur MCP Builder

Workflow

Check the current Mailosaur docs before changing tool coverage.
Prefer the official mailosaur Node.js client over hand-written HTTP calls when building a TypeScript MCP server.
Map each Mailosaur operation to a focused MCP tool with Zod input schemas and clear descriptions.
Keep secret values in environment variables. Require MAILOSAUR_API_KEY; never write keys into examples except as placeholders.
Return JSON as MCP text content. Return downloaded files as base64 content with an encoding field.
Require an explicit confirm: true field for destructive operations such as deleting messages, deleting all messages, deleting servers, or deleting devices.
Verify with npm run typecheck and npm run build.

References

Read references/mailosaur-api.md when checking tool coverage, parameter names, destructive operations, or documentation links.

Tool Coverage Checklist

Cover these groups when the user asks for a full Mailosaur MCP:

Messages: get/wait, list, search, get by ID, create, forward, reply, delete, delete all, generate previews.
Servers: list, create, get, get password, update, delete, generate email address.
Files: get email EML, get attachment, get preview screenshot.
Analysis: spam and deliverability.
Usage: limits and transactions.
Devices: list, create, OTP, delete.
Previews: list email clients.

GitHub Readiness

Include or update:

README.md with setup, MCP config, tool list, and official docs links.
LICENSE.
.gitignore and .npmignore.
.github/workflows/ci.yml running npm ci, typecheck, and build.
CONTRIBUTING.md and SECURITY.md when publishing publicly.

Files

What ships with it

2 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.

12d ago First seen · 43 lines · 79 tokens per session scan A dcb3d863af51

Subscribe to this mod's changes

mailosaur-mcp-builder is a skill published in the GitHub repository MrNewDelhi/mailosaur-mcp (0 stars, last pushed 3mo ago), licensed MIT. It adds 79 tokens to every session and 485 once invoked, about $0.0004 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 2026-08-31.

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