mcptee

mcptee - tool for MCP developers to log stdin transport

8 stars GoDeveloper Kits Updated Jun 18, 2025

Documentation

# mcptee

A simple tool that proxies input from MCP client to MCP server and returns the output back to the client, while also logging both to the file line by line indicating the direction of the data with a prefixes "in:" and "out:", resulting in a file that is normally valid YAML.

Before every "in:", tool would print `---` and endline that would make file multi-document YAML, so normally every combination of request/respons would be a separate document.

This could be pretty handy for testing and troubleshooting MCP clients and servers.

## Installation

## npm

bash

npm install -g @strowk/mcptee

## Github Releases

Download prebulit binaries from the releases page and put in your PATH

## Build from source

bash

go install github.com/strowk/mcptee@latest

## Usage

bash

mcptee   [args...]

Some examples:

bash

mcptee ./server_log.yaml mcp-k8s-go

mcptee ./server_log.yaml npx @strowk/mcp-k8s

You would probably configure it with corresponding client. For example, with Claude:

json

{
    "mcpServers": {
        "my_server": {
            "command": "mcptee",
            "args": ["/path/to/log_file.yaml", "npx", "my_mcp_server"]
        }
    }
}

## Example

If you have for example a postgres server running in docker:

bash

docker run --rm --name postgres-mcp-test -e POSTGRES_PASSWORD=thesecret -p 7777:5432 postgres:latest

, and you want to test it with mcp-server-postgres (run it in another terminal):

bash

mcptee log.yaml npx @modelcontextprotocol/server-postgres postgres://postgres:thesecret@localhost:7777

Now send these one by one:

json

{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"testing","version":"0.0.1"}}}

{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}

{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"query", "arguments": {"sql": "SELECT datname FROM pg_database"} }}

You should see the output in the `log.yaml` file like this:

yaml

---
in: {"jsonrpc":"2.0","id":0,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"testing","version":"0.0.1"}}}
out: {"result":{"protocolVersion":"2024-11-05","capabilities":{"resources":{},"tools":{}},"serverInfo":{"name":"example-servers/postgres","version":"0.1.0"}},"jsonrpc":"2.0","id":0}
---
in: {"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}
out: {"result":{"tools":[{"name":"query","description":"Run a read-only SQL query","inputSchema":{"type":"object","properties":{"sql":{"type":"string"}}}}]},"jsonrpc":"2.0","id":1}
---
in: {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"query", "arguments": {"sql": "SELECT datname FROM pg_database"} }}
out: {"result":{"content":[{"type":"text","text":"[\n  {\n    \"datname\": \"postgres\"\n  },\n  {\n    \"datname\": \"template1\"\n  },\n  {\n    \"datname\": \"template0\"\n  }\n]"}],"isError":false},"jsonrpc":"2.0","id":1}

Frequently asked questions

What is mcptee?

mcptee is mcptee - tool for MCP developers to log stdin transport

How do I install mcptee?

Open the GitHub repository and follow its README. Most MCP servers are added to your client's MCP config, then called by your agent.

Is mcptee open source?

Yes — it is hosted on GitHub at https://github.com/strowk/mcptee/ and has 8 stars.

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