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

Annotations already declare read-only, idempotent, non-destructive, open-world, so the description correctly spends its words elsewhere: dual pricing (0.005 USDC via x402 or 3 credits), the 5-free-calls-per-day quota, and the Kadaster BAG/PDOK provenance. That cost and free-tier context is exactly the kind of behavior annotations cannot express.

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 trigger, then output fields, use cases, source and cost. Three sentences, each earning its place; the pricing sentence is long but essential for a paid tool. Minor redundancy between the title and the opening clause.

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?

With no output schema, the description compensates by listing the returned fields and sort order, and it covers payment/auth paths so the agent knows what to do without a key. It doesn't say whether all addresses for a postcode fit in one response or how large a postcode payload typically is.

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% – both postcode format and the api_key flow are documented in the schema. The description adds no parameter syntax or constraints beyond that, 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 and resource ('every address in a Dutch postcode') and enumerates the returned fields (street, house number, letter, addition, BAG id, coordinates) plus ordering. This clearly separates it from single-address siblings like nl_address_lookup and nl_address_reverse without needing to name them.

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?

Explicit trigger ('Use when you need every address in a Dutch postcode') plus concrete use cases: address pickers, delivery/canvassing routes, data cleaning. It never states when NOT to use it or names the single-address/batch alternatives, so it stops short of a 5.

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