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

readOnlyHint=true already declares this as a non-destructive read, so the safety profile is covered. The description adds the underlying REST route, but says nothing about 404 behavior for unknown ids, error shape, or what the response contains. With annotations carrying the safety burden, this is adequate but thin.

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, front-loaded with the operation and the key to use. The API route line is compact and helps confirm the exact resource being fetched; nothing is padded or repeated.

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 with rich annotations this is close to sufficient, but with no output schema the description never hints at the returned customer fields or what happens on a missing id. A brief note on the response or error case would close the 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 is documented as "the customer external unique identifier (from your application)". The description repeats "by external id" but adds no format, casing, or example-value detail beyond the schema, so the baseline of 3 applies.

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 ("Retrieve a single customer") and pins the lookup key ("by external id"), which implicitly separates it from lago_list_customers and the usage/portal siblings. It stops short of naming the sibling explicitly, so an agent must infer the single-vs-list distinction.

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?

Usage is implied by "single customer by external id" – an agent can reasonably infer this is the direct-lookup path versus lago_list_customers. However, there is no explicit when-to-use guidance, no prerequisites, and no named alternative as in stronger definitions.

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