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

Annotations already declare readOnlyHint, openWorldHint=false, and destructiveHint=false, so safety is covered. The description adds real behavior beyond them: the price is denominated in wallet currency, numbers held by another workspace are silently omitted, and paging is cursor-based. It stops short of describing the returned fields or how price/currency are represented.

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 short sentences, each carrying a distinct fact: what is listed, what is excluded, and how to page. The core scoping statement is front-loaded and there is no filler.

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 five-parameter, zero-required, read-only search with full schema coverage and no output schema, the description supplies the key non-obvious facts (purchase intent, cross-workspace exclusion, cursor paging). The main remaining gap is the absence of any guidance about the profusion of similar number-listing tools, which matters given this sibling set.

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 coverage is 100%, so limit, cursor, search, country, and purpose are already documented, including format hints like the two-letter code example. The pagination sentence ("pass next_cursor back as cursor") restates what the cursor parameter description already says, adding no new semantics. 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?

"Lists phone numbers the workspace can buy, priced in its wallet currency" gives a concrete verb plus resource and a purchase-oriented scope. It does not, however, distinguish itself from near-duplicate siblings like search_available_numbers, list_numbers, or desk_list_numbers, so an agent cannot route between them from the text alone.

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?

Framing the result as numbers "the workspace can buy" implies the pre-purchase use case, and the exclusion of numbers held by other workspaces implies the availability filter. There is no explicit statement of when to use this instead of the sibling search/listing tools, nor any prerequisite about needing wallet balance.

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