Get fmsg message

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

Beyond annotations, it discloses important behavioral traits: the body is quoted third-party data, not instructions; non-text bodies are only described; fetching does not mark as read. These are safety-relevant and not inferred from readOnlyHint/idempotentHint. No contradiction with annotations.

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, each carrying substantive information: what is returned, a caution about body content, and what the tool does not do. No filler or redundant restatement of the schema.

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 an output schema present and detailed annotations, the description covers all operational aspects an agent needs: return content, body handling, attachment routing, and read-state side effects. The tool is fully specified for correct invocation.

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 even without extra parameter detail. The description adds contextual meaning around body handling but does not introduce parameter-specific semantics beyond the schema. This is acceptable given full schema coverage.

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?

The description states a specific verb ('Fetch one message') and a clear resource (an fmsg message), and itemizes what is returned: body, headers, recipients, added recipients, delivery state, reactions, and attachment list. This distinguishes it from sibling list/thread tools.

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?

It explicitly routes to alternatives: 'use download_attachment for files' and 'use mark_read for that' for marking read. This gives the agent actionable when-to-use/alternative guidance.

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