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

The readOnlyHint=true annotation already establishes this is a safe read, but the description adds no behavioral context beyond that: no 404 handling for an unknown code, no pagination/rate-limit notes, and nothing about what is returned. It essentially only restates the REST route.

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 sentences, the purpose is front-loaded, and the API route is appended as supporting detail. Nothing is wasted or 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 one-parameter read tool with an annotation covering safety and no output schema, the definition is minimally adequate. It could still note failure behavior for an invalid code or briefly characterize the returned metric object.

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 with 100% schema description coverage, so the schema already documents 'code' as the unique code. The description's 'by code' merely echoes the schema, which is the baseline 3 case.

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+resource ('Retrieve a single billable metric') and scopes it to one record via 'single' and 'by code', which distinguishes it from the sibling lago_list_billable_metrics. It does not name that sibling explicitly, so it falls just short of 5.

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 'by code' implies you need a code in hand, so usage is inferable, but there is no explicit when-to-use statement, no mention of the alternative list tool, and no guidance on what to do if the code is unknown.

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