ros2-mcp-server

read_topic

Retrieve the latest message from a ROS2 topic, returning serialized data and message age in milliseconds. Supports latched topics for static data like /map or /robot_description.

Instructions

Read the latest message from a ROS2 topic. Returns the serialized message and data age in milliseconds. For latched topics (/map, /robot_description), set latched=true.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "topic": "<topic>"
    },
    "name": "read_topic"
  }
}

Input Schema

Name	Required	Description	Default
`topic`	Yes	Topic name, e.g. '/scan'
`latched`	No	Set true for topics published once on connect (/map, /robot_description)
`msg_type`	No	ROS2 message type, e.g. 'sensor_msgs/LaserScan'	std_msgs/String
`timeout_ms`	No	Max wait time in milliseconds

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.1.0Aug 11, 2026

TDQS

A3.9/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Discloses return payload (serialized message, data age) and latched behavior. However, no annotations are present, and it fails to mention timeout/failure behavior or what happens if no message is available. Moderate transparency.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two concise sentences that front-load the core purpose and include a practical usage tip. No wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Adequate for a simple read tool with good schema coverage. However, no output schema exists, so the description should more precisely define the return structure beyond 'serialized message'. Also omits error and timeout behavior.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so baseline is 3. Description adds a note about latched topics, but this is already in the schema. No significant additional parameter meaning beyond schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Clearly states the verb 'read' and resource 'ROS2 topic', and specifies it retrieves the latest message. Distinguishes itself from sibling tools like list_topics and publish_topic.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit conditional guidance for latched topics ('set latched=true'). Does not discuss when to use this tool instead of alternatives, but the context is clear for this read operation.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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