Find related mail threads

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

It discloses the underlying heuristic (normalized-subject overlap + participant overlap), the configured default scope, and both false-negative and false-positive behaviors. It also explains the limit parameter's truncation behavior and that the total is still reported, adding non-obvious context beyond the readOnlyHint annotation.

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 well-organized: purpose paragraph, heuristic/limitations paragraph, and a clear Args list. Each sentence adds meaningful information without redundancy; it is detailed yet entirely relevant.

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?

Despite lacking an output schema, the description conveys that the tool returns related thread leads and mentions the truncation total reporting. It also provides reliability caveats, giving the agent sufficient context to invoke the tool and interpret its results appropriately.

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 schema provides no parameter descriptions, but the Args section fully explains thread_id (including the optional 'thread:' prefix) and limit (default null, capping behavior, and truncation reporting). This completely compensates for the 0% schema-description coverage.

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 opens with a specific verb+resource: 'Find other threads that might be the same topic coming up again.' It clearly distinguishes the tool from siblings by focusing on related-thread discovery rather than general search or reading. The heuristic-vs-semantic contrast further differentiates it from mail_search.

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 how to use the results: 'Treat the result as a lead to check with mail_read_thread, not as a definitive answer.' It also contrasts with semantic search, giving clear context about when this tool is appropriate and what its limitations are.

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