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

Annotations already cover readOnlyHint/idempotentHint/destructiveHint, and the description's "Read only." duplicates that, but the enumeration of verification states (none, pending_review, in_review, approved, rejected) with Twilio's rejection reason is genuinely additive context an agent cannot get from the annotations.

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?

One front-loaded sentence plus a two-word clarification; the returned fields are listed compactly and nothing is wasted. No redundant preamble or restatement of the title.

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?

The tool is a simple single-record read with a full output schema, so return-value explanation is technically unnecessary, and the safety profile is fully covered by annotations. The only missing piece is sibling disambiguation, which is minor at this complexity.

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?

A single required id parameter with 100% schema description coverage, so the schema already explains the num_… format and its origin from list_numbers. The description adds no further meaning about the identifier, which is consistent with the baseline for fully documented params.

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: reads one business number, and enumerates the fields returned (state, fee paid until, toll-free verification). The singular "One business number" implicitly distinguishes it from list_numbers/search_numbers, though it never names those siblings.

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?

Usage is only implied: an agent infers this is the single-record read used after obtaining an id, and the routing to list_numbers lives in the schema parameter description rather than the tool description. No explicit when-not or alternative is given (e.g. list_numbers for enumerating, search_numbers for lookup by number).

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