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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely new context: the source of truth (Resporgs.com and the toll free registry's records) and the ordering of results (newest first), which the annotations cannot convey.

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 sentences, front-loaded with what the tool returns followed by when to use it. The clause defining RespOrgs is a useful inline gloss, and nothing is padded, though the third sentence restates return contents that overlap with the output schema.

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 tool with full annotation coverage and an output schema, the description supplies everything an agent needs: the source, the temporal ordering, the trigger scenario, and a pointer to the external page. No relevant gap remains.

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 already documents accepted formats with examples (800-356-9377, 1-800-FLOWERS). The description adds no additional syntax or formatting guidance, so the schema does all the work here.

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?

Names a specific resource (a toll free number's history) and enumerates exactly what is returned: which RespOrgs held it, when, and its status in each span. This is clearly distinguishable from siblings like check_number or search_vanity_numbers, which serve different lookup intents.

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?

Gives a concrete triggering condition: use it when someone asks who previously held a number or how long it has been with its current company. It does not, however, name an alternative tool for the overlapping 'who owns this number now' question, so the agent must infer the boundary against check_number.

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