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

Annotations only declare readOnlyHint=true; the description adds genuine context beyond that, notably scope ("any document id this business owns") and a data-interpretation pitfall: a document's totals are header $total/$vat, while $linetotal is pre-VAT and pre-discount, so lines must not be summed to quote totals. It doesn't cover failure behavior for unknown or unauthorized ids, keeping it short of a 5.

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?

Front-loaded with the core action and return contents, then usage routing, then total semantics. Every sentence carries information, though the final sentence is dense and slightly overpacked with accounting caveats.

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?

No output schema exists, so the description does the work of describing the return shape (totals, status, lines, contact, money direction) and the meaning of the monetary fields. What's missing is only edge-case behavior for invalid or foreign-owned ids.

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?

With one required parameter and 100% schema coverage, baseline is 3; the description earns an extra point by defining what counts as a valid id (invoice, quote, credit-note ids returned by list_documents and list_invoices), which the schema's bare "Document id." does not convey.

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 ("Get one document by id") and enumerates what comes back: totals, status, line items, contact, money direction. It also distinguishes itself from list_documents/list_invoices by naming them as sources of ids, so an agent can tell the retrieval tool from the list tools without opening 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?

Gives explicit operating instructions: find the id yourself via list_documents (query by number or contact) and never ask the user for an id. It also clarifies that invoice, quote and credit-note ids from list_documents and list_invoices are all valid inputs, which removes the main ambiguity in choosing this tool.

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