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

Annotations already declare readOnlyHint=true, and the description's 'Fetch' and 'GET /v1/email/messages/{message_id}' are consistent with a read operation. The description adds the single-resource scope and API method, but doesn't disclose additional behaviors such as error handling or response format.

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 one sentence, front-loaded with the action and resource, and includes the API endpoint as a helpful reference. No wasted words.

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?

For a simple getter with one parameter, readOnlyHint annotation, and no output schema, the description is sufficient. It scopes the operation and provides the endpoint, though it doesn't detail the return payload.

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?

The input schema already provides full coverage with a description for message_id ('Email message id.'), so the baseline is 3. The description's 'by id' reinforces the parameter but doesn't add new semantics beyond the schema.

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 uses a specific verb ('Fetch'), specifies the resource ('a single email message'), and identifies the selection key ('by id'). It clearly distinguishes from sibling tools like bird_list_email_messages (listing) and bird_get_sms_message (different channel).

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 implies usage by indicating the operation takes an id, but it does not explicitly state when to choose this over bird_list_email_messages or other getters. There is no exclusions/alternatives mentioned.

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