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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior; the description's 'Side effects: none (read-only)' restates that rather than adding new behavioral detail. It adds the useful context that contact groups are Fax.Plus tags, but no further behavioral traits are disclosed.

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 and front-loaded, with the core purpose in the first sentence. The second sentence is redundant with the annotations but does not create significant bloat.

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 read-only list operation with a full output schema and 100% schema-described parameters, the description covers the essential purpose and confirms no side effects. It could be improved by explicitly routing between this and sibling list tools, but nothing critical is missing for invoking 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?

Schema description coverage is 100%, with all five optional parameters documented in the schema. The description only refers generically to 'optional pagination and filters' and adds no semantic information beyond the schema, so the baseline 3 applies.

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 uses a specific verb ('List') and a specific resource ('contact groups'), and the parenthetical '(Fax.Plus tags)' clarifies domain terminology. This distinguishes it from sibling tools like create-contact-group, delete-contact-group, and list-contacts.

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 tool's purpose as a read-only list operation is clear, so when to use it is implied. However, the description does not explicitly mention alternatives or exclusions, such as using list-contacts for contacts rather than groups.

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