mcp-tracer

wireshark for MCP — intercept, log, and visualize every tool call your agent makes.

install

npx @safetnsr/mcp-tracer

usage

trace an MCP server

mcp-tracer proxy -- npx @modelcontextprotocol/server-filesystem .

view the report

mcp-tracer report

Output:

┌──────────────────┬───────┬──────────────┬─────────────┬───────────┐
│ Tool             │ Calls │ Total Latency│ Avg Latency │ Bytes     │
├──────────────────┼───────┼──────────────┼─────────────┼───────────┤
│ read_file        │   847 │      4,235ms │       5.0ms │   2.1 MB  │
│ write_file       │    12 │        156ms │      13.0ms │  45.2 KB  │
│ list_directory   │     3 │         18ms │       6.0ms │   1.2 KB  │
└──────────────────┴───────┴──────────────┴─────────────┴───────────┘

Session: 862 calls | 4.4s total | 2.1 MB transferred

list sessions

mcp-tracer list

use with Claude Desktop

In your claude_desktop_config.json, change:

"command": "npx @modelcontextprotocol/server-filesystem ."

to:

"command": "npx @safetnsr/mcp-tracer proxy -- npx @modelcontextprotocol/server-filesystem ."

One line change. Full tracing.

flags

| flag | description | |------|------------| | --help | show help | | --version | show version | | --json | output report as JSON |

agent interface (--json)

{
  "session": "2026-03-08_17-30-00",
  "totalCalls": 862,
  "totalDurationMs": 4409,
  "tools": [
    { "method": "read_file", "calls": 847, "totalLatencyMs": 4235, "avgLatencyMs": 5.0, "totalBytes": 2100000 }
  ]
}

pair with

• @safetnsr/vet — audit your agent's code changes
• @safetnsr/pinch — track session costs