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

readOnlyHint=true already tells the agent this is a safe read, lowering the bar. The description adds the invoice-specific expansion targets, which is useful behavioral detail about how to get a full breakdown, but says nothing about permissions, rate limits, or error behavior for a missing id.

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 short sentences: purpose first, then the highest-value parameter hint, then the underlying endpoint. No filler and nothing buried.

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 read-only single-resource fetch with no output schema and full schema coverage, the description covers purpose, key parameter usage, and the endpoint. It stops short of describing what the breakdown contains or pagination, but no essential calling information is missing.

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's generic expand example by naming the five invoice-specific expansions (line_items, charges, discounts, taxes, applied_credits). That is concrete meaning the schema does not supply.

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 by id'), which unambiguously distinguishes it from the sibling goteamup_list_invoices. The endpoint hint (GET /invoices/{id}) reinforces scope without ambiguity.

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 operational guidance for the expand parameter ('use expand=line_items,charges,... for the breakdown'), which is a real usage cue, but never states when to reach for this tool versus goteamup_list_invoices. Usage is implied rather than explicitly routed.

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