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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, and the description adds real context on top: data source (Kadaster BAG via PDOK), dual pricing (0.002 USDC via x402 or 1 API-key credit), and the first-5-calls-a-day free allowance. Payment and auth mechanics are exactly the kind of behavioral fact annotations cannot convey.

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, then outputs, then input format, then cost. Four dense sentences, each carrying distinct information; nothing is redundant with the title or 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?

No output schema exists, yet the description enumerates the returned fields and their meaning (distance in metres, administrative hierarchy, nearby addresses), so the agent knows exactly what to expect. Inputs, cost, auth and data provenance are all covered for a 3-parameter read tool.

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 the baseline is 3, but the description adds the datum (WGS84) and currency (degrees, with the examples 52.0836 / 4.2919), which is meaningfully beyond the schema's bare "Latitude" label. It also frames the api_key parameter through the credit-vs-x402 payment model.

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 operation (coordinates → nearest official BAG address) and enumerates the exact return payload: distance in metres, postcode, city, municipality, province, BAG ids, CBS buurt/wijk codes, plus neighbours. This is clearly distinguishable from address-lookup siblings such as nl_address_lookup or nl_postcode_addresses, which take the opposite direction of input.

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 you have coordinates in the Netherlands and need the address" gives a concrete triggering condition, and the payment note implies when the free tier is exhausted. It stops short of naming alternatives (e.g. nl_address_lookup for address→coordinates, nl_address_batch for bulk), so the agent must infer the routing itself.

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