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

readOnlyHint=true already declares this is a safe read, so the description's main addition is the underlying endpoint (GET /api/v0/contacts/{id}) and the { meta, response } envelope, which is genuinely useful since there is no output schema. It says nothing about error behavior (e.g. missing id) or auth requirements.

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 compact fragments, front-loaded with the purpose before the endpoint and return shape. The endpoint line is mildly redundant for an agent but earns its place by anchoring the return envelope.

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 two-parameter read tool with no output schema, the description covers purpose, endpoint, and response envelope, which is close to sufficient. Only the absence of any error/permission note keeps it from fully 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?

Schema description coverage is 100%, so both 'id' and the '_fields' escape hatch are already documented in the schema. The description adds no syntax, format, or constraint detail beyond that, making the baseline 3 appropriate.

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?

States a specific verb ('Fetch') and resource ('a single contact (a person)'), with 'single' implicitly contrasting against the sibling list_contacts and create_contact. It never names an alternative explicitly, but the resource and cardinality are unambiguous.

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?

No when-to-use guidance is given: nothing says to use this when you already have an id, nor that list_contacts is the alternative when you don't. The reader must infer the calling context entirely from the name and schema.

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