The Everything server is Anthropic’s reference implementation of the Model Context Protocol. It exists to exercise the spec: every feature the protocol defines is implemented somewhere in it, which makes it the standard way to check whether a client handles MCP properly. It is a development tool rather than something you would connect to get work done.
What it actually does
It exposes a deliberate sample of the protocol surface. There are tools that echo input and do simple arithmetic, resources you can list and read, prompt templates, and demonstrations of the parts people implement last: sampling, progress notifications and multi-step interactions. Nothing it returns is useful data; the value is in watching how your client behaves when it receives each kind of message.
Practical patterns:
- Point a client you are building at it and confirm every capability negotiates correctly.
- Reproduce a protocol bug in isolation, away from a real server’s logic.
- Read the source when you are implementing a feature and the spec alone is ambiguous.
Why use it
If you are writing an MCP client, this is the fixture you test against. If you are writing a server, it is the clearest single answer to “what does a correct implementation of this feature look like”. The protocol documentation describes the contract; this shows it running.
Gotchas
Leaving it installed in a client you actually use is the mistake to avoid. Every server in a session contributes its tool definitions to the context window, and a server full of echo and add tools gives the model a set of plausible-looking but pointless options. Install it deliberately, use it, and remove it when you are done.
