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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds useful return-content context ('including its line items'), which annotations cannot convey, but it omits error behavior (e.g., missing/invalid id) and auth requirements.

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?

Two short, front-loaded sentences with zero filler: the first states the action and return scope, the second gives the REST endpoint. Every element earns its place.

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-resource read with one fully documented parameter, readOnlyHint annotations, and no output schema, the description is nearly sufficient. The addition of line-item inclusion is helpful; only minor details like error handling are 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 description coverage is 100% and the single required parameter invoice_id is fully documented in the schema with type and constraint. The description's 'by id' adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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 (Retrieve) and resource (a single invoice by id) and adds the scope qualifier 'single', which distinguishes it from the sibling harvest_list_invoices without naming it directly. The REST mapping (GET /invoices/{id}) further pins down the operation.

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: the word 'single' and 'by id' suggest this is for fetching one known invoice rather than listing, but no alternatives (e.g., harvest_list_invoices) or conditions are stated explicitly. No when-not guidance or prerequisites are given.

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