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

The description adds value beyond annotations by detailing the return value ({marked: true}), error handling (404 for unknown thread), and the effect of 'archived' status (hides from default inbox, refetching behavior). No contradiction with annotations.

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 concise (three sentences plus a front-loaded purpose). Every sentence adds necessary information with no fluff.

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 the two parameters, no output schema, and available sibling tools, the description provides complete context: input details, output, errors, and usage boundaries.

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?

While schema coverage is 50%, the description adds meaning by listing the valid status values and explaining the archival behavior. It also provides context for threadId ('e.g. from inbox() or campaign events'). This compensates for the missing schema descriptions.

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 clearly states the verb 'Set' and the resource 'a thread's READ-STATE' for inbox triage. It also explicitly distinguishes from sibling tools 'label_thread' and 'reply'.

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 explains when to use the tool (for read/unread/archived flags) and provides alternatives for other actions (label_thread for labels, reply for responses). However, it does not explicitly state when not to use it beyond those comparisons.

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