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

readOnlyHint=true already tells the agent this is a safe read, so the bar is lower. The description adds genuine value by disclosing the shape of the result (line items, taxes, discounts, payments, totals, amount due) in the absence of an output schema, though it omits error/not-found behavior and any auth or rate-limit context.

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 tight sentences with zero filler; the purpose and the returned fields are front-loaded and the API mapping (GET /invoices/{id}) is appended last where it does not interrupt reading.

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 one-parameter read tool with no output schema, the description covers both the operation and the returned content, which is what an agent most needs. It stops short of error handling and alternative selection, leaving only minor gaps given the low complexity.

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?

There is a single parameter (invoice_id) with 100% schema description coverage, so the schema fully documents it. The description adds no syntax, format, or sourcing detail for the id, 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?

States a specific verb and resource ('Fetch one invoice') and enumerates what the response contains (line items, taxes, discounts, payments, totals, amount due). The singular 'one invoice' implicitly separates it from intakeq_list_invoices, but the sibling is never named, so differentiation relies on inference.

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: needing the details of a known invoice by id. There is no explicit when-to-use guidance, no mention of when to prefer intakeq_list_invoices, and no note on what to do if the id is unknown or the invoice is not found.

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