Mark messages

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

Beyond annotations (idempotentHint=true, destructiveHint=false), the description adds that the operation is 'cheap and reversible,' which clarifies its benign nature. This provides useful context not present in structured fields, though it does not cover all possible behaviors (e.g., no rate limits or auth details).

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 two sentences, front-loaded with the purpose, and every word earns its place. No redundant or vague phrasing, making it highly 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 6 parameters, 1 required, and an output schema (handling return values), the description covers the main operations and a key constraint. It could elaborate on multiple message handling or interactions between parameters, but it is sufficiently complete for a marking tool.

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?

With 0% schema coverage, the description compensates by listing the actions (read, flagged, junk, add_tags, remove_tags) and directing to `mail_tags` for tag values. This adds meaning beyond the schema's types and defaults, though it could explain the effect of null defaults (no change) more explicitly.

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 tool sets read/flagged/junk state or adjusts tags on messages, specifying the verb 'set' and the resource 'messages'. It distinguishes from siblings like folder_mark_read, mail_delete, and mail_tags by focusing on per-message marking operations.

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 notes that the operation is 'cheap and reversible, so no confirmation is required,' providing guidance on when it is safe to use. It also references `mail_tags` for valid tag keys, implying a prerequisite. However, it does not explicitly compare to alternatives or state when not to use this tool.

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