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

No annotations are provided, so the description carries the full behavioral burden. It usefully discloses that this is a paid x402 endpoint ($0.001/call in USDC on eip155:8453) and states dataset scope/coverage, but says nothing about error behavior (unknown code), rate limits, or response shape.

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?

Two tight sentences: purpose and both usage modes are front-loaded, with pricing appended. Slightly telegraphic in the pricing clause, but no padded or redundant text.

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 3-parameter tool with no annotations and no output schema, the description covers purpose, modes, and dataset scope, which is close to sufficient. However, it never resolves the schema oddity that code, state, and limit are all required while the schema says code may be left empty to list by state, leaving an agent unsure how to invoke the listing mode.

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%, so the schema already documents all three parameters. The description corroborates the code/state relationship but adds no format detail (e.g. valid code shapes, whether limit is optional in practice). Baseline 3 applies when the schema does the heavy lifting.

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+resource ('Look up any US telephone area code') plus an explicit second mode ('list every area code in a given state'), and scopes the data ('all 404 NANP codes in use, including overlays'). Easily distinguished from the nearest sibling, databases_countries.

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?

The description makes the two operating modes explicit: pass a code to resolve a state, or list by state. That gives clear context for which parameter drives which behavior, but it offers no exclusions or guidance on when to prefer one mode over the other in a workflow.

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