Read an invoice

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

Annotations already cover readOnly, idempotent and non-destructive semantics, but the description adds genuine behavior: the store-scoping fallback (searches every connected store when omitted) and the not_found error when no store has the id. It also enumerates return fields, which matters because no output schema exists. It stops short of mentioning auth or rate-limit behavior, so not a full 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 purpose and scope, followed by return shape, then the store/error caveat, then the sibling redirect. The return-field list is dense but justified given there is no output schema, and no sentence is redundant.

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 two-parameter read tool with no output schema, the description supplies exactly what is missing: the return payload shape (including nested payment fields and smallest-unit amounts), fallback scoping behavior, and the failure mode. Nothing an agent needs to call and interpret it correctly is absent.

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 the baseline is 3, but the description goes beyond the schema by explaining where a valid invoiceId comes from and clarifying that omitting store triggers a cross-store search. Those are behavioral semantics the schema alone would 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?

The description opens with a specific verb+resource ("Gets one invoice by its id") and immediately scopes it to the case where the id is already known. It distinguishes itself from the sibling list_invoices by naming it directly as the lookup-by-criteria alternative.

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 states when to use this tool ("when you already have the id, for example from create_invoice or list_invoices") and explicitly routes the agent elsewhere for status/reference/date lookups. That is a clear when/when-not pairing with the alternative named.

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