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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and a closed-world scope, so safety is fully covered. The description adds value beyond them by disclosing the returned payload (status, lists, tags, custom fields) and by implying that one lookup key must be supplied even though the schema marks neither as required.

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?

Two short statements, payload listed first and the lookup keys second, with no filler. It is slightly too compressed: the opening noun fragment "One contact with..." would read better with an explicit verb such as "Retrieve".

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 with rich annotations and no output schema, the description covers the essentials and partially compensates for the missing output schema by enumerating the returned fields. It does not describe the shape of nested data like custom fields or what an unknown id returns, which keeps it below 5.

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 coverage is 100%, so both parameters are already documented, which sets the baseline at 3. The description contributes the either/or lookup semantics ("id or its email address") that the schema does not express, but adds no format details or precedence rules, so it stays at the baseline.

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?

"One contact with its status, lists, tags and custom fields" states the resource (a single contact) and the payload it returns, which implicitly separates it from search_contacts. It lacks an explicit verb and never names the sibling it contrasts with, so differentiation is inferred rather than stated.

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?

"Give the contact's id or its email address" is really parameter guidance, not when-to-use guidance. Nothing says when to prefer this over search_contacts, nor what happens if the contact doesn't exist.

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