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

Annotations already indicate idempotentHint=true and readOnlyHint=false, but the description adds critical behavioral detail: it debits €2 from the wallet, is idempotent per (buyer, entity) with no second charge on retry, and returns HTTP 402 with a payment requirement and top-up URL if the balance is insufficient. It also clarifies the agent earns spending ability after a human top-up. This goes well beyond the annotation hints and fully discloses the side effects and error states.

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 longer than typical but every sentence serves a purpose: purpose, payment mechanism, idempotency, error handling, and alternative tool routing. It is front-loaded with the primary goal and structured logically, making it easy to parse. No fluff; each detail is essential for correct invocation.

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 single-parameter purchase tool with no output schema, the description covers all necessary aspects: what it does, what it returns, side effects (payment), idempotency, error handling, prerequisites, and related tools for obtaining input. The guidance on 402 handling is especially complete, telling the agent to hand top-up to a human and then retry. Nothing essential 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?

The single parameter 'id' is well-described in the schema ('Entity id (uuid) from search_entities / resolve.') with 100% schema coverage. The description reinforces this by repeating the source of the id, which adds helpful context about where to obtain it. While the schema already covers the semantic meaning, the description adds a pointer to the upstream tools, which is valuable for agent usage.

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 clearly states the tool's purpose: 'BUY the full dossier for one entity programmatically' with specific details on what is returned (premium dossier with UBO chain, financials, etc.). It also distinguishes itself from the sibling tool buy_dossier by labeling this the 'AGENT-NATIVE purchase path' versus the 'human/browser path'. This makes it unmistakable what the tool does and how it differs from alternatives.

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 provides explicit usage guidance: it explains when to use this tool (agent purchases) and the alternative (buy_dossier for human/browser), how to get the id ('from search_entities / resolve'), and error handling instructions (top-up and retry). It also sets prerequisites ('Requires a funded API key'). This leaves no ambiguity about when and how to invoke it.

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