mcap-mcp-server 0.1.0

A generic SQL query interface for MCAP robotics data via the Model Context Protocol

mcap-mcp-server

A generic SQL query interface for MCAP robotics recording data via the Model Context Protocol.

Status: Alpha — Core implementation with all encoding decoders (JSON, Protobuf, ROS 1, ROS 2, FlatBuffers).

What It Does

Point this MCP server at a directory of MCAP files and query them with SQL — no database server, no ETL pipeline, no custom scripts.

MCAP files → mcap-mcp-server → DuckDB (in-memory) → SQL results

Works with Cursor, Claude Desktop, or any MCP-compatible client.

Quick Start

# Install
pip install mcap-mcp-server

# Or zero-install via uvx
uvx mcap-mcp-server --data-dir /path/to/recordings

MCP Client Configuration

Cursor (.cursor/mcp.json)

{
  "mcpServers": {
    "mcap-query": {
      "command": "uvx",
      "args": ["mcap-mcp-server"],
      "env": {
        "MCAP_DATA_DIR": "/path/to/recordings"
      }
    }
  }
}

Claude Desktop (claude_desktop_config.json)

{
  "mcpServers": {
    "mcap-query": {
      "command": "uvx",
      "args": ["mcap-mcp-server"],
      "env": {
        "MCAP_DATA_DIR": "/path/to/recordings"
      }
    }
  }
}

Available Tools

Tool	Description
list_recordings	Discover MCAP files: names, sizes, durations, channels
get_schema	Inspect SQL table names, column names and types for query planning
load_recording	Decode MCAP data and load into DuckDB for SQL querying
query	Execute SQL against loaded data (full DuckDB SQL including ASOF JOIN)

Typical Workflow

1. Discover available recordings:

   → list_recordings
   

2. Inspect the schema to plan queries:

   → get_schema file="session_001.mcap"
   

3. Load data into DuckDB:

   → load_recording file="session_001.mcap"
   

4. Query with SQL:

   SELECT timestamp_us, voltage, current
   FROM battery
   WHERE voltage < 22.0
   ORDER BY timestamp_us
   

Example Queries

-- Time-windowed statistics (1-second windows)
SELECT
  (timestamp_us / 1000000) as second,
  AVG(voltage) as avg_voltage,
  MIN(voltage) as min_voltage
FROM battery
GROUP BY second
ORDER BY second

-- Correlate battery with acceleration using ASOF JOIN
SELECT
  b.timestamp_us,
  b.voltage,
  i.linear_acceleration_x
FROM battery b
ASOF JOIN imu i ON b.timestamp_us >= i.timestamp_us

-- Compare across multiple loaded recordings
SELECT 'run1' as recording, AVG(voltage) as avg_v FROM r1_battery
UNION ALL
SELECT 'run2' as recording, AVG(voltage) as avg_v FROM r2_battery

-- Search metadata
SELECT * FROM _metadata WHERE key LIKE '%serial%'

Configuration

Environment Variables

Variable	Default	Description
MCAP_DATA_DIR	.	Root directory to scan for MCAP files
MCAP_RECURSIVE	true	Scan subdirectories recursively
MCAP_MAX_MEMORY_MB	2048	Max memory for loaded data (LRU eviction)
MCAP_QUERY_TIMEOUT_S	30	Max SQL query execution time
MCAP_DEFAULT_ROW_LIMIT	1000	Default result row limit
MCAP_MAX_ROW_LIMIT	10000	Maximum allowed row limit
MCAP_LOG_LEVEL	INFO	Server log level
MCAP_TRANSPORT	stdio	Transport: stdio or sse
MCAP_SSE_PORT	8080	Port for SSE transport
MCAP_FLATTEN_DEPTH	3	Max nesting depth for message flattening

Config File (optional)

Create mcap-mcp-server.toml:

[server]
data_dir = "/data/recordings"
recursive = true
transport = "stdio"

[limits]
max_memory_mb = 4096
query_timeout_s = 60
default_row_limit = 1000
max_row_limit = 50000

[decoder]
flatten_depth = 3

[logging]
level = "INFO"

Environment variables override config file values.

Supported Encodings

Encoding	Install
JSON	pip install mcap-mcp-server (built-in)
Protobuf	pip install mcap-mcp-server[protobuf]
ROS 1	pip install mcap-mcp-server[ros1]
ROS 2 (CDR)	pip install mcap-mcp-server[ros2]
FlatBuffers	pip install mcap-mcp-server[flatbuffers]
All encodings	pip install mcap-mcp-server[all]

Docker

docker run -d \
  -v /data/recordings:/data:ro \
  -e MCAP_DATA_DIR=/data \
  -e MCAP_TRANSPORT=sse \
  -p 8080:8080 \
  ghcr.io/turkenberg/mcap-mcp-server:latest

Development

git clone https://github.com/turkenberg/mcap_mcp_server.git
cd mcap_mcp_server
git submodule update --init
pip install -e ".[dev]"
pytest

License

GNU General Public License v3.0 — see LICENSE.