MailDev vs Mailcatcher

A factual comparison of MailDev and Mailcatcher, two open-source local SMTP catchers — runtime, install, web UI, API surface, relaying, and AI agent support.

Both MailDev and Mailcatcher are open-source SMTP "catchers": you point your app at a local SMTP port and outgoing mail is trapped and shown in a web UI instead of reaching real inboxes. They solve the same core problem. Here is how they differ.

At a glance #

Comparison compiled in good faith from public documentation and may go out of date. Corrections welcome via a GitHub issue.

Where they genuinely overlap #

For the core job — catch mail, show it in a browser, never send it to a real person — either tool works, and both have been doing it for over a decade. If you already have Mailcatcher running and it does what you need, there is no urgent reason to switch.

Both catch on an SMTP port, both render HTML and plain text, both show raw source and headers, both handle attachments, both push new mail to the UI over a websocket, and both are MIT licensed.

Pick MailDev if #

• You work in JavaScript or TypeScript. npx maildev needs no Ruby toolchain, and MailDev can be a devDependency pinned in your lockfile.
• You care about the UI. Search, a command palette, responsive preview at phone and tablet widths, and a dark theme.
• You script your inbox from tests. The REST API covers listing with pagination and search, reading, deleting in bulk, marking read, downloading, and relaying — see testing email in CI.
• You want it in-process. The programmatic API starts and stops MailDev inside a Node.js test suite and emits an event per message, which removes the polling from email assertions entirely.
• You want an AI agent to read the inbox. The built-in MCP server gives Claude, Cursor, Codex, and other MCP clients tools for searching and reading your dev mail.
• You need to forward mail onward. Relay and auto-relay can push caught messages to a real SMTP server, with allow/deny rules.

Mailcatcher fits if #

• Your stack is Ruby-first and gem install mailcatcher fits your tooling better than npm.
• You want the smaller, long-established tool and none of the extras above matter to you.

Switching #

There is nothing to migrate — a catcher holds no state you care about. Both default to SMTP on 1025, so if you have been using Mailcatcher's defaults, your application configuration already works:

npx maildev

The web UI moves from Mailcatcher's port 1080… which is also MailDev's default. In practice the only change is which process you start.

If you script against Mailcatcher's API, the endpoints differ — see the REST API reference for MailDev's, which is under /api and returns richer message objects.

Other options #

MailDev is not the only alternative. Mailpit and MailHog are the Go-based tools in this space, smtp4dev and Papercut serve the .NET world, and Mailtrap is the hosted option. Comparisons for those are on the way — if there is one you particularly want, say so on the issue tracker.

Last updated 2026-08-25·Edit this page·View as markdown