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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds two things annotations do not: the 'at least one filter required' rule (which the schema does not enforce, since only mailbox is required) and the shape of the return value (summaries with uids). It still says nothing about result limits or pagination.

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 tight sentences: capability and filter dimensions first, the hard constraint second, return format last. No filler and nothing redundant.

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?

For a ten-parameter read tool with no output schema, the description covers scope, filter dimensions, the key constraint, and the return shape. It stops short of noting result limits, ordering, or how it relates to list_messages, which keeps it from being fully complete.

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 100%, so every one of the ten parameters is already documented in the schema. The description groups the filters (from, to, subject, body, date range, attachments), which mirrors but does not extend the schema. Baseline 3 applies when the schema does the heavy lifting.

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?

States a specific verb and resource (search a mailbox folder) and enumerates the filter dimensions, plus what it returns (message summaries with uids). It implicitly scopes to one mailbox/folder, which differentiates it from the search_all_mailboxes sibling, but it never names that sibling explicitly.

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?

Gives one real constraint — 'At least one filter is required' — but offers no guidance on when to use this versus list_messages or search_all_mailboxes, nor any prerequisite or exclusion. Usage context is implied rather than stated.

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