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

Annotations only declare readOnlyHint and openWorldHint, but the description adds genuinely non-obvious traits: results are limited to the first page (~30 listings), a market summary is included, and the call costs $0.002 USDC via x402 with failed calls not charged. The payment/auth model and the result cap are exactly the kind of behavior an agent needs before invoking a paid tool; only rate limits or per-city coverage caveats are missing.

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?

The first sentence front-loads the resource, source and returned fields; the second gives scope; the third gives cost. It is dense but every clause carries information. The price sentence could arguably be trimmed, but it is billing-critical and short.

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 an output schema present and full parameter coverage, the description is not required to explain return values, yet it usefully adds the first-page/~30-listing cap and the x402 cost model that structured fields do not express. For a read-only, open-world scraping tool this covers the essentials; only explicit alternatives to sibling property sites are absent.

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%, with city, deal (buy/rent) and type (apartment/house) fully documented in the schema. The description restates the same axes ('for a city', 'Apartments or houses, to buy or rent') without adding format or constraint detail beyond the schema, so the 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?

The description names a specific resource and source ('German property listings from immowelt.de for a city') and enumerates the per-listing fields plus a market summary, so the agent knows exactly what it gets. Geography ('German') implicitly separates it from the many other country-specific realestate siblings, but no sibling is named explicitly and the retrieval verb is implied 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?

Usage is only implied: the agent can infer this is the tool for German cities and that it handles both 'Apartments or houses, to buy or rent'. There is no statement of when not to use it, no alternative named among the large realestate sibling set, and no prerequisites beyond the payment note.

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