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

With no annotations, the description carries the full burden and does well: it warns that include_blocks can return many more rows (a volume/cost signal) and explains result semantics, e.g. thousands=-1 is the whole-prefix aggregate while 0-9 are individual pooling blocks. It omits auth prerequisites and pagination behavior, though the api_key parameter covers auth in the schema.

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 leads the description, followed by usage triggers, the risky flag, and field/value interpretation — each sentence adds information. The field inventory sentence is somewhat long but earns its place by telling the agent what comes back without an 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 three-parameter read tool with no annotations and no output schema, the definition is essentially self-sufficient: it covers purpose, trigger conditions, the expansion flag, and the field/value shape of the response. Only auth flow and row-count expectations are left thin.

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 baseline is 3; the description adds genuine meaning by explaining when include_blocks should be flipped and how to interpret the thousands values in results. It does not restate or clarify the npa pattern beyond what the schema already documents.

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?

The description states a specific verb and resource: list all exchanges/prefixes within a given NANP area code. It is clearly narrower than sibling get_exchange (single prefix) or lookup_tn, but it never names an alternative tool, so differentiation is inferred rather than stated.

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?

It gives concrete triggering scenarios (area-code inventory, coverage, 'what prefixes exist in 425') and an explicit rule for the one optional flag: only set include_blocks=true for thousand-block/pooling detail. It lacks explicit routing to the many list_* siblings, but the when-to-use and when-to-expand guidance is clear.

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