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

Annotations already provide readOnlyHint=true, and the description's 'Fetch' and 'GET' are consistent with that. The description adds little beyond what annotations and the name convey—it mentions the API endpoint and single message scope but does not disclose error behavior, rate limits, or return format. With annotations covering safety, this addition is marginal but acceptable.

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 a single, front-loaded sentence: 'Fetch a single WhatsApp message by id. Bird API: GET /v1/whatsapp/messages/{message_id}.' Every word earns its place, and it is not verbose or redundant.

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 get-by-ID tool with one parameter, read-only annotation, and no output schema, the description is sufficiently complete. It specifies the exact resource and operation, and the schema fully documents the parameter. It does not describe the response fields, but that is not critical for tool selection/invocation given the simplicity and lack of output schema. A 4 reflects very good completeness without being perfect.

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%: the only parameter message_id is described as 'WhatsApp message id.' The description's 'by id' and endpoint placeholder {message_id} adds no extra semantic meaning beyond the schema. Baseline 3 is appropriate because the schema fully documents the 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?

The description clearly states 'Fetch a single WhatsApp message by id', which is a specific verb+resource+scope. It distinguishes from siblings like bird_get_email_message (different channel), bird_get_sms_message (different channel), and bird_list_whatsapp_messages (plural 'list' vs singular 'single').

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 for a single message lookup via 'single' and 'by id', providing clear context. However, it does not explicitly mention alternatives or when not to use, such as using bird_list_whatsapp_messages for multiple messages or bird_get_email_message for email messages. Thus it falls short of a 5 but is above a 3.

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