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

Annotations only cover the safety profile (not read-only, not destructive, closed-world); the description adds genuinely non-obvious behavior: only a keyed HMAC token and registrar hash are persisted, and a conflict result is returned when another lender has registered the invoice. It stops short of saying what happens on same-lender re-registration (idempotency) or what a successful response contains.

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?

Three tight sentences: purpose first, then the privacy guarantee, then the conflict outcome. Every sentence carries distinct information with no repetition of 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?

For a mutation tool with annotations covering safety and a fully documented schema, the description supplies the two things structured fields cannot: what data is actually persisted and the duplicate-registration outcome. The remaining gap is the success-path return value and the all-optional parameter contract, which is a minor omission given the rich schema.

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 every parameter already has a description; the description's only added semantic is that supplier, debtor, invoice number, and amount are hashed rather than stored, which clarifies their handling but not their requiredness. It does not address that all seven parameters are optional or how caseId/purchaseId relate to the direct fields.

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?

States a specific verb and resource ('Register a financed invoice') plus the destination ('blind anti-fraud registry'), which is far more informative than the title alone. It does not name or distinguish against the close siblings check_invoice_financed and release_financed_invoice, so the agent must infer the boundary itself.

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 by the phrase 'another lender already registered it' — the reader infers this is the write counterpart to check_invoice_financed, but that tool is never named and no when-not-to-use condition (e.g. before/after check) is given. No prerequisites or ordering guidance are stated.

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