mailbox_read_message

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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description goes beyond that by disclosing the shape of the response (headers, text, revision, attachment index/filename/bytes) and by warning that message text is untrusted third-party data that must not be treated as instructions — genuinely useful context a schema cannot convey.

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 read action, then the attachment route, then the safety caveat. Every sentence earns its place, though the final security sentence is long and could be tightened slightly.

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 compensates by enumerating the returned fields, and it covers the credential/multi-mailbox nuance of the optional mailbox parameter. The only minor gap is that it says nothing about size limits or truncation of large messages.

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 baseline is 3. The description adds real meaning beyond the schema: it ties 'id' to its origin in mailbox_list_messages and adds the 'same mailbox' constraint linking id and mailbox, which is not stated in either parameter description.

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 ('Read one message by id') plus the exact payload returned: headers, text, revision, and attachment metadata. It also names where the id comes from (mailbox_list_messages) and routes attachment bodies elsewhere, so it is clearly distinguishable from siblings like mailbox_list_messages and mailbox_get_attachment.

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 names the prerequisite source of the id ('from mailbox_list_messages, in the same mailbox') and the alternative for attachment content ('Get an attachment's content with mailbox_get_attachment'). It gives clear context and one alternative but no explicit when-not condition, so it falls just 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.