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

readOnlyHint=true already tells the agent this is a safe non-mutating read, so the description carries a lower burden. It adds the endpoint path but discloses nothing beyond annotations such as error behavior for missing ids or whether expansions affect payload size.

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, front-loaded with the core action, followed by the most actionable parameter tip and the endpoint. No filler.

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, the description covers purpose, the id requirement, and the useful expand set. It could note return shape or not-found behavior, but nothing critical for correct invocation 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 adds genuine value by naming the concrete invoice-specific expand values (line_items, charges, discounts, taxes, applied_credits) that the generic schema example does not provide.

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 with scope ('Fetch one invoice by id'), which cleanly distinguishes it from the sibling goteamup_list_invoices. The API endpoint reference reinforces the exact resource addressed.

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 a practical hint about which expand values are useful for invoices, but never states when to use this single-fetch tool versus goteamup_list_invoices or other lookups. Usage is only implied by the word 'one'.

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