get_contact

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is known. The description adds behavioral value by specifying the return format (JSON contact object) and the fields included (uid, full_name, name, etc.), which the annotations do not cover. This extra context enriches the agent's understanding beyond the structured metadata.

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 concise with a clear structure: a one-sentence summary, then Args and Returns sections. It is front-loaded with the purpose. The only minor inefficiency is repeating the schema's parameter defaults, but overall it earns its place.

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 tool's low complexity (2 params, 1 required), annotations cover safety, and there is an output schema, the description is largely complete. It explains the key parameter semantics and return shape. The only minor gap is not specifying error behavior (e.g., what happens if UID is invalid), but this is not critical for basic usage.

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 0%, so the description must compensate for undefined parameters. It does: it explains 'uid' is the contact UID and directs to get_contacts for discovery, and states 'book_id' is the address book ID with a default. This adds crucial meaning that the schema lacks, effectively compensating for the coverage gap.

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 specific verb and resource ('Get a single contact by UID') and clarifies the scope (single contact, not a list), distinguishing it from the sibling 'get_contacts'. It also lists the fields returned, leaving no ambiguity about what the tool does.

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?

It explains when to use this tool (to get a single contact) and explicitly mentions how to find UIDs via 'get_contacts', effectively routing to the correct sibling. However, it does not explicitly state when NOT to use it, but the contrast with get_contacts is clear enough.

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