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

Annotations already indicate read-only, idempotent, non-destructive behavior, and the description reinforces this with 'Side effects: none (read-only).' It also discloses a non-obvious behavior: response groups appear as names even though the API stores IDs, because the tool resolves them.

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 compact, well-organized, and front-loaded with the core purpose and filters. The workflow sentence earns its place because it encodes critical ordering constraints, and the side-effect note is short and reassuring despite being partially redundant with annotations.

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 an 11-parameter read-only list tool with a full input schema and an output schema, the description covers the essential operational context: filtering, pagination, sorting, shared/personal scope, fax workflow ordering, group-name resolution, and the explicit no-side-effects guarantee. An agent has everything needed to invoke it correctly.

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?

The schema already covers all 11 parameters at 100%, so the baseline is 3. The description adds value beyond the schema by showing example filter syntax (name=Jane), recommending limit 20 in fax workflows, and explaining that groups are resolved from IDs to names in the response.

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: 'List contacts' and immediately enumerates the available filters, pagination, sorting, and shared/personal modes. It is unambiguous and clearly distinguishable from contact-group or fax-list sibling tools.

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 gives explicit when-to-use guidance: use filters like name=Jane rather than client-side filtering, and in fax workflows always call this tool after pipeline_start and list-numbers but before request-file-from-user. It also instructs the agent not to ask the user for a contact, which is a concrete exclusion.

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