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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false. The description adds useful behavioral context beyond annotations: newest-first ordering, returned thread ids, and the downstream read/reply workflow, though it omits rate limits or pagination behavior.

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?

Two sentences are tightly front-loaded with purpose, searchable fields, return value, and follow-up workflow. Every phrase earns its place with no filler.

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?

There is no output schema, but the description explains that thread ids are returned and how to use them with read_email_thread and reply tools. Annotations cover safety and schema covers most parameters, leaving only minor gaps around pagination or empty-result behavior.

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?

Schema description coverage is 80%, so the baseline is 3. The description restates the query fields and participant address but does not add syntax, defaults, or constraints for limit, state, or unread_only beyond what the schema already provides.

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 a specific verb and resource: searching the user's connected mailbox threads. It also scopes the search fields and ordering, and distinguishes the output from read_email_thread, so an agent can identify the tool without opening the schema.

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?

It explains the discovery workflow: use this to get thread ids for read_email_thread, and use draft_email + reply_to_thread_id to reply. It does not explicitly say when not to use it or name alternative search tools, so it falls short of full alternative guidance.

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