Get Checkout invoice

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds behavioral value by specifying the returned data (status, URL, amounts), which is not expressed in the annotations. No contradictions or undisclosed side effects are present.

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?

The description is a single sentence that front-loads the core action ('Look up'), specifies the resource, and lists the key outputs. Every word earns its place, with no redundancy or 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?

This is a simple single-parameter read operation, the annotations fully cover its side-effect profile, an output schema exists to describe return values, and the description states the essential return fields. Nothing material is missing for an agent to select and invoke the tool correctly.

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% — the only parameter, invoiceId, is already documented with 'Invoice id returned by create_invoice.' The description adds no additional parameter meaning beyond saying lookup is by id, so the baseline of 3 is appropriate.

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 uses a specific verb ('Look up') and a specific resource ('a known FinCobra Checkout invoice by id'), clearly distinguishing it from sibling tools like create_invoice or list_sources. It also states the key return contents (status, hosted payment URL, amounts), leaving no ambiguity about the tool's function.

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?

The phrase 'a known invoice by id' makes it clear this tool is for retrieving an existing invoice, not for creating or listing. It implies the invoice id comes from a prior create_invoice call, which sets context. However, it does not explicitly name alternatives or exclusion conditions, so it stops short of full guidance.

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