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

Annotations declare readOnlyHint=true, so safety is covered; the description adds the API path, that results come back as a Feed, and the honest caveat that the shape is inferred from the API's List model, which is meaningful context beyond the annotations.

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?

Purpose and return fields are front-loaded, followed by the endpoint and the caveat. The NOTE sentence is slightly dense but earns its place by flagging model-inference risk.

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?

With readOnlyHint annotations, no output schema, and full param schema coverage, the description supplies the missing pieces: what a List is, what it returns, the endpoint, and the escape-hatch fallback. Little an agent needs to call it correctly is absent.

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 page/pagesize/takesize and the params filter bag. The description adds little parameter-level detail (only that lists carry ListID/ListName), 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?

States a specific verb+resource ("List saved contact lists") and clarifies the domain with "(groups you can broadcast to)", plus names the API endpoint GET /v1/lists. This clearly separates it from siblings like list_broadcasts, list_text_numbers, and get_broadcast.

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?

Provides explicit conditional routing: if the account/endpoint differs, use the textemall_request escape hatch, and the schema's params note repeats that rule for range operators. It lacks general when-to-use framing, but the alternative-tool guidance is concrete.

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