Read a message

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

Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower, yet the description still adds genuinely useful behavior: HTML is silently converted to text unless html=true, and the call 'changes nothing (does not mark the message as read)'—a non-obvious behavior in mail clients. It omits any mention of size limits or permission requirements for shared mailboxes, 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?

Three sentences, front-loaded with the core purpose and return payload, then alternatives, then the side-effect constraint. No filler and nothing repeated from structured fields.

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?

With no output schema, the description properly compensates by naming the returned fields (headers, text body, attachment list) and the HTML conversion behavior. Coverage is strong, though an agent still lacks any note on size limits or how attachments must be fetched separately in bulk.

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 all three parameters (id, html, account) are already documented in the schema; the baseline is 3. The description only adds provenance for the required id (comes from mail_search_emails) and implies the html behavior, without new meaning for the account parameter.

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 ('Returns a whole message by id') and enumerates exactly what comes back: headers, converted body text, and the attachment list. It also distinguishes itself from mail_get_attachment and mail_send_email, so an agent can place it among its siblings without opening a 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?

Explicitly says where the id comes from ('from mail_search_emails'), routes attachment reading to mail_get_attachment, and directs replies to mail_send_email with in_reply_to_id. Both the when-to-use and the alternative-routing conditions are stated outright.

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