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

Annotations declare readOnlyHint=true, and the description discloses the HTTP method (GET) and endpoint, which reinforces safety. It adds the exact resource path, which is useful. However, it does not explain error behavior (e.g., 404 if not found), auth requirements, or response format. With annotations covering the safety profile, a score of 3 is appropriate.

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 concise sentences, including the purpose and the API endpoint. No wasted words. All information is directly useful and easy to parse.

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?

This is a simple tool with one parameter, no output schema, and read-only annotation. The description provides the endpoint and purpose, which covers the core need. However, without an output schema, it does not mention what the response contains (e.g., contact fields), which could be a gap for agents expecting structured output. Given the low complexity, the description is almost complete.

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 has 100% coverage for the single parameter contact_id, with description 'Contact id.' The tool description also refers to 'by id', so the parameter's meaning is fully clear from the schema. The description adds no extra syntax or format details beyond the schema, so the baseline of 3 applies.

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 'Fetch a single contact by id' uses a specific verb ('Fetch') and resource ('a single contact') with a clear scope ('by id'), distinguishing it from siblings like bird_list_contacts (which lists multiple) and other bird_get_* tools. The explicit API endpoint further clarifies the exact purpose.

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 clearly implies usage: when you have a contact_id and need a single contact. It provides clear context ('by id') and even specifies the API endpoint. However, it does not explicitly mention alternatives (e.g., bird_list_contacts for multiple contacts), but the singular framing makes this obvious.

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