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

Annotations already declare readOnlyHint=false, idempotentHint=false, and destructiveHint=true. The description adds useful behavior beyond annotations by saying 'Not retried', stating it returns the new contact id, and giving the API endpoint; it does not explain why destructiveHint=true or permission 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?

The description is short, front-loaded with the write operation, and every sentence adds actionable information. It avoids repeating schema details while still covering duplicate avoidance, retry behavior, return value, and endpoint.

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 create mutation with full schema coverage and annotations, the description covers duplicate avoidance, retry risk, return value, and endpoint. It omits permissions/auth details and deeper duplicate-handling behavior, but no output schema exists and the key call guidance is present.

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 the schema already documents all five parameters in detail. The description adds only high-level context that a name is required and optionally one email and one phone can be supplied; phone_type semantics remain with the schema.

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 starts with a specific verb and resource: 'create a new person contact in Rex'. It states the required name and optional one email/one phone, and names rex_autocomplete_contacts for duplicate checks, making it distinguishable from get/search siblings.

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 explicitly tells the agent to search first via rex_autocomplete_contacts to avoid duplicates. It does not give broader when-not-to-use guidance or mention other search/create alternatives, but the primary usage condition is clear.

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