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

Annotations already declare readOnlyHint=false, idempotentHint=false, and destructiveHint=false, so the safety profile is covered. The description adds valuable non-annotation context: the contact is shared with everyone in the Rinkel account, and calls from its numbers display its name. This goes beyond structured fields, though it does not explain duplicate-contact behavior.

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 tightly written sentences front-load the write operation and then add sharing scope and the API endpoint. The API endpoint may be marginally less useful to an agent, but overall there is no wasted prose.

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 mutation tool with no output schema, the description covers the key sharing side effect but omits important details such as duplicate handling, whether the contact can be edited later, and the significance of the required numbers array. Annotations cover safety, but the low parameter coverage leaves gaps.

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 only 33%, so several parameters lack documentation in both schema and description. The description references 'numbers' only through the sharing behavior and does not explain the required numbers array, default_outbound_number_id, or the name/company fields. It fails to compensate for the low schema coverage.

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: 'WRITE: create a contact.' It clearly distinguishes creation from sibling tools like rinkel_update_contact and rinkel_list_contacts, so an agent can identify its purpose without opening the schema.

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 'WRITE' prefix and 'create a contact' imply this should be used when adding a new contact, but the description does not explicitly say when to use this versus rinkel_update_contact or how to check for duplicates. Usage is implied rather than guided.

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