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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld false). The description adds useful non-annotation context: the data source (NewLocalNumbers.com) and the 18-month recency window that defines 'new'. It does not add auth or rate-limit notes, but the covered traits are meaningful.

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 scope are front-loaded in the first sentence, with the usage cue and return summary following. Efficient overall, though the return enumeration ('up to 10 blocks, companies..., links...') is somewhat verbose given an output schema exists.

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 full parameter coverage, annotations declaring the safety profile, and an output schema covering returns, the description supplies everything an agent needs to select and invoke the tool correctly, including source and recency semantics.

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 both parameters are already documented, making 3 the baseline. The description adds only the marginal detail that scope is US or Canadian, which slightly extends the schema's area-code/state framing.

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 ('Find') and resource ('newest blocks of local phone numbers') plus scope (US/Canadian area code or state) and an example block format (512-687-4xxx). This clearly separates it from siblings like check_number, number_history, and search_vanity_numbers.

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?

Explicitly names the triggering situations: 'when someone wants a new local number in an area, or asks which phone company has new numbers there.' Strong context, but no when-not guidance and no sibling alternative is named for cases where the agent should route elsewhere.

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