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

With no annotations, the description carries the full burden and does well: it discloses result ordering (newest first), the projected fields, and the important side-effect that 'nothing is marked read'. It does not cover pagination behavior, rate limits, or auth requirements, which keeps it from a 5.

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, densely packed and front-loaded: what it returns and how it is ordered first, filters and the no-mark-read guarantee second, routing last. Every clause carries information.

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, and the description compensates by enumerating the returned fields and their order. Combined with 100% parameter coverage and the explicit hand-off to mail_read, an agent has everything needed to call this correctly.

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 the schema already documents all seven parameters, including defaults and the YYYY-MM-DD format. The description restates the filter dimensions (words in subject and body, sender, start date, unread only) but adds no syntax or scope detail beyond what the schema 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?

States a specific verb (Find) and resource (messages in a mailbox folder), enumerates the exact fields returned (uid, sender, recipients, subject, date, unread flag) and the ordering (newest first). It also explicitly distinguishes itself from the sibling mail_read, so an agent can route between them without opening either 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?

Names the alternative and the condition that selects it: search here, then 'Pass a uid to mail_read' for the body. It also names mail_folders and mail_accounts as the sources for folder/mailbox values. There is no explicit when-not guidance (e.g. for attachments or large result sets), so it falls short of a 5.

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