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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), so credit goes to what the description adds: the two data sources, the 'up to 10 of each' result cap, and the connected/disconnected distinction. It doesn't mention rate limits or auth needs, but the behavioral picture is materially richer than the annotations alone.

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?

Front-loaded with the core action and use case in the first clause, then supporting detail. The closing sentence on return values is partly redundant given the output schema exists, but the prose stays dense and waste-free.

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 single-parameter, read-only lookup with a rich annotation set and an output schema, the description supplies the sourcing, result cap, and the browse-vs-search distinction an agent needs. Return-value detail is slightly over-explained given the output schema, but nothing essential 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% and the single parameter is fully documented, so the baseline is 3. The description's examples (PLUMBING, DENTIST, LAWYER) merely restate the examples already in the schema, adding no new constraint or format detail.

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 concrete verb and resource ('Find toll free numbers for a type of business') and immediately scopes it to category-level browsing rather than single-word search, which separates it from siblings like search_vanity_numbers and find_new_local_numbers. The sources (1800AVAILABLE.com, 1800DISCONNECT.com) make the resource unambiguous.

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?

Explicit trigger: 'Use it when someone wants to browse numbers for their kind of business rather than one word.' This gives a clear when-to-use condition and contrasts with the single-word alternative, though it never names that sibling tool or states exclusions for check_number/number_history.

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