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

Goes well beyond the annotations by disclosing the pricing model (0.08 USDC via x402 or 40 credits of a Factline API key) and the free tier of five paid calls per day, which is exactly the kind of precondition an agent must know before invoking. It also describes the return content (best address per metric plus a full per-address report).

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 triggering condition, followed by scope, output, input format and cost in a compact sequence. Only the short repeating input line is slightly redundant, and it costs a few words.

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 one-parameter, read-only tool with no output schema, the description covers the trigger, the address-count bounds, the metrics returned, and the payment preconditions. Nothing material needed to call it correctly 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 already documents the ';'-separated 2-to-5-address format with an example. The description's "Input: addresses separated by ';'" merely repeats the schema, so baseline 3 applies.

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 (compare) and a tightly bounded resource (2 to 5 Dutch addresses), then enumerates the metrics compared and the output shape. An agent can tell it apart from single-address siblings like nl_address_lookup, though no sibling is named explicitly.

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?

"Use when the user is choosing between 2 to 5 Dutch addresses" gives a clear selection condition that naturally excludes single-lookup and bulk-list tools. It stops short of naming an alternative or stating when-not to use it.

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