Read a message

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, covering the safety profile. The description adds meaningful behavioral details beyond that: body is converted to text, truncated at 25,000 characters, and includes unsubscribe options from headers. This provides concrete expectations about output format and limits, adding value without contradicting 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?

The description is two sentences with no filler. The first sentence front-loads the primary purpose and lists what is returned; the second sentence adds the truncation limit. Every piece of information earns its place, and the structure is efficient and scannable.

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?

Given the single-parameter schema, the presence of an output schema, and annotations covering safety and idempotency, the description provides all essential context: what content is returned, how it's formatted, and the truncation limit. No additional information is needed for correct invocation, so it is complete for this tool's complexity.

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 does not add any parameter-specific information beyond the schema; it never mentions the 'id' parameter or its format. The schema already documents that the id comes from mail_search or mail_senders_summary, so the description adds no extra semantic value.

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 clear verb ('Return') and resource ('full content of one message'), and enumerates specific included elements (body as text, recipients, attachment flag, web link, unsubscribe options). This distinguishes it from siblings like mail_search (which lists messages) and mail_unsubscribe (which acts on subscriptions). The purpose is unambiguous and specific.

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?

The description does not explicitly state when to use this tool versus alternatives, nor does it name any exclusions. However, it implies usage for retrieving a single message's full details after locating an id via mail_search or mail_senders_summary. The contrast with siblings is inferable but not spelled out, so the guidance is implicit rather than explicit.

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