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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real context beyond that: a 750000-byte size ceiling, an untrusted-content/prompt-injection warning, and the binary-file exclusion. It does not say whether oversized files error or truncate, which is the one remaining behavioral gap.

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?

Front-loaded verb+resource+scope, followed by alternatives, security note, and exclusion. Five short sentences, each carrying distinct information; nothing is padding.

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?

Output schema exists so return values need not be explained. Purpose, size limit, sibling routing, security posture, and binary exclusion are all present, leaving nothing an agent needs in order 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 coverage is 100% and the schema already documents path, account_id, reason, and mailbox_id in detail. The description adds no parameter-level syntax or format guidance, so baseline 3 applies.

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 (Read) and resource (one text mailbox file) with explicit scope (HTML/CSS/JS/JSON/Markdown, up to 750000 bytes), and carves itself out from the email-specific siblings in the same sentence set.

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?

Explicitly routes the agent: 'For email, prefer mailbox_email_list and mailbox_email_get... and mailbox_email_download for attachments or original EML', plus a hard exclusion ('Not for binary files'). Both when-to-use and when-not-to-use are stated, with named alternatives.

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