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

Annotations (readOnlyHint, openWorldHint) already cover safety, and the description adds genuinely useful behavior beyond them: the rolling-12-month aggregation window, and the privacy trait that 'no individual is ever named' and the breakdown is withheld when it would single someone out. The api_key parameter also discloses that insufficient credit returns a credits error rather than an x402 quote. No contradiction with annotations.

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 description is a single dense paragraph, front-loaded with the core purpose and question, then content breakdown, privacy behavior, use case, and pricing. Every sentence earns its place, though the pricing sentence is somewhat redundant with the api_key parameter description. Efficient and well ordered, with only minor redundancy.

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 4-parameter tool with an output schema, the definition is complete: it covers what data is returned (notification counts, gross buy/sell amounts, net flow, declarer category breakdown, underlying notifications), behavioral caveats (privacy withholding), the time window, usage context, and payment. The output schema covers return values, and annotations cover safety, so nothing material 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%, so the schema fully documents all four parameters (id, depuis, api_key, x_payment), placing the baseline at 3. The main description ties loosely to the parameters — the rolling 12-month window maps to 'depuis' and payment mechanics map to x_payment/api_key — but it does not add significant syntax or format meaning beyond the schema.

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+resource: it retrieves insider transactions for a Belgian listed company, framed around MAR Article 19 and FSMA notifications with the sharp question 'are its managers buying or selling?'. The 'Belgian' qualifier plus the regulatory specifics clearly distinguish it from the sibling get_german_insider_transactions, so an agent can tell them apart without inspecting schemas.

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?

It gives an explicit use case — 'Use it as a governance signal before investing in or contracting with a listed Belgian company' — which is clear contextual guidance. It stops short of naming alternatives or exclusions (e.g., 'for German companies, use get_german_insider_transactions'), so it earns a 4 rather than a 5.

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