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

Annotations already declare readOnlyHint=true, and the description reinforces this with 'Deposits are immutable.' Beyond annotations, it discloses meaningful behavioral traits: return format varies by filing date (structured JSON since April 2022 vs. base64 PDF for older filings), and the payment requirement with exact cost ($0.15 USDC/EURC via x402). This is rich context the annotations do not provide.

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?

Four compact sentences, each earning its place: the core purpose, date-based format variance, input provenance, immutability, and cost. The most important scoping information is front-loaded, and there is no filler or repetition of schema content.

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?

The description covers the essential operational facts: what is returned, format by date, where the reference comes from, immutability, and cost. The two-step payment flow (omit x_payment to get a quote) is handled by the schema's x_payment description, so it need not be repeated. Minor gap: no output schema exists and the description does not hint at the JSON shape of the financial-statement data, though the category of data is stated.

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 baseline is 3. The description adds value beyond the schema by establishing the provenance of the reference parameter ('Reference comes from list_belgian_company_filings') and by explaining the payment context that relates to x_payment and api_key. This elevates it above baseline without fully documenting parameter mechanics.

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 verb and resource: retrieving one Belgian annual-account deposit 'as filed' from NBB CBSO Authentic Data. It clearly distinguishes itself from sibling tools — it is country-specific (Belgian) and singular ('One deposit'), which contrasts with list_belgian_company_filings and the other country filing getters like get_danish_company_filing.

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 explicitly routes the agent to the upstream tool: 'Reference comes from list_belgian_company_filings,' telling it where to obtain the required reference parameter. It does not explicitly state when not to use the tool or name alternatives, but the Belgian-specific scope and the reference provenance provide clear selection context.

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