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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds real behavioral context on top: results come back in alphabetical order, `all` is the default filter, and the underlying endpoint is GET /{account}/contact_filters/{filter}/contacts. Pagination limits and result caps are not described, keeping it short of a 5.

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?

Three tight sentences: the core operation and ordering come first, then the two filter parameters, then the API mapping. Nothing is redundant and no sentence is padding.

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 four-parameter list tool with full schema coverage and no output schema, the description covers operation, ordering, defaults, and backend mapping. Minor gaps remain around whether `all` includes opt-outs and what the page size is, but nothing blocking correct invocation is missing.

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 baseline is 3. The description largely restates the schema — `q` searches name or phone, `contact_filter` defaults to `all` — without adding syntax, matching rules, or cursor mechanics beyond what the properties already say.

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 and resource ("List contacts of an account") plus return ordering (alphabetical), which clearly separates it from textus_get_contact and textus_list_group_contacts by implication. It never names a sibling explicitly, so differentiation relies on the reader inferring list-vs-get semantics.

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 description explains how to use two parameters (search with `q`, saved view via `contact_filter`, default `all`), which implies when to use the tool. It gives no explicit when-not guidance or named alternative (e.g., use textus_list_group_contacts for group membership), so the agent must infer the boundaries.

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