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

Annotations already indicate a non-read-only, non-idempotent mutation. The description adds an explicit side effect ('creates contact') and the target context (address book), but it does not discuss duplicate behavior or whether existing contacts are affected. This is adequate but not rich.

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, and skimmable. The only minor redundancy is the final 'Side effects: creates contact' line, which repeats the first sentence.

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 9-parameter tool with full schema coverage and an output schema, the description covers the required inputs and the likely confusion point (group names vs IDs). It omits duplicate/permission details, but those are not essential given the annotations and schema.

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 every parameter is already documented in the schema. The description merely emphasizes the required fields and the groups-vs-IDs gotcha, both of which are already present in the schema descriptions.

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 opens with a specific verb and resource: 'Create a new contact in Fax.Plus address book.' This clearly differentiates it from siblings like update-contact, delete-contact, and create-contact-group.

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 states necessary prerequisites: name and fax_number are required, and groups must be group names rather than IDs. It does not explicitly name alternatives like update-contact or delete-contact, but the create intent and required fields make the usage context unambiguous.

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