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

readOnlyHint=true already tells the agent this is a safe read, and the description is consistent with that ('Retrieve'). It adds the underlying API route (GET /invoices/{lago_id}) but says nothing about error behavior for an unknown id or what the returned object contains.

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 no waste; the identifier and the endpoint mapping are the only information present, and both earn their 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 one-parameter read tool with readOnlyHint coverage, the definition is nearly sufficient to invoke correctly. Without an output schema, a brief note on what the invoice object returns would have closed the remaining gap.

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 parameter lago_id is already documented as a UUID in the schema, so the description's 'by its Lago id' adds no semantics beyond it. Baseline 3 is appropriate when the schema does the heavy lifting.

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 (Retrieve) and resource (a single invoice) keyed by Lago id, which implicitly separates it from the sibling lago_list_invoices. It stops short of naming the alternative explicitly, so the distinction must be inferred from the word 'single'.

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?

There is no when-to-use guidance and no mention of the sibling lago_list_invoices as the alternative for bulk retrieval. The only signal is 'single invoice' in the purpose sentence, which is implied rather than stated as a selection rule.

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