start_replay_session

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

No annotations are provided, so the description carries the burden. It mentions that the returned session_id works with other tools and lists reverse-execution capabilities, but it does not disclose potential side effects, resource locks, or permission requirements. More behavioral context would be beneficial.

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

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

The description is front-loaded with purpose, then workflow, then param details. It is generally concise, though the list of reverse-execution tools could be seen as slightly redundant given those are separate sibling tools. Overall, it is efficient.

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

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

Given no output schema, the description should more explicitly mention the return format. While it says 'The returned session_id', it does not specify that the tool returns an object containing session_id. Also, it lacks error conditions or session lifecycle details, making it moderately complete for a tool with two optional parameters.

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

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

The input schema has 0% description coverage, but the description provides brief explanations for both parameters: 'trace_dir: trace directory from rr_record; omit to replay the most recent recording' and 'cwd: working directory for rr (defaults to current directory)'. This adds meaningful context beyond the schema.

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

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

The description states 'Start an rr replay session for time-travel debugging. Step 2 of the rr workflow.', which clearly identifies the tool's purpose and distinguishes it from sibling tools like rr_record and start_session. It provides a specific verb and resource.

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

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

The description explicitly states the prerequisite: 'Call rr_record first to produce a trace, then call this tool.' This gives clear guidance on when to use the tool and positions it within the workflow.

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