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

Annotations already declare readOnlyHint=true, indicating a safe read operation. The description adds the retrieval method (by external id) and the API endpoint, but does not disclose additional behaviors such as rate limits, authentication requirements, or potential error states. Given the annotation coverage, the description provides marginal additive value.

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 extremely concise: one sentence stating the purpose and one sentence for the API endpoint. Every word is functional, no redundancy. It is front-loaded with the core action and resource.

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 simple read-only tool with one parameter and no output schema, the description is complete. It specifies the input (external id) and the result (retrieve a single customer). No additional context is needed given the tool's simplicity and the annotations covering safety.

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% for the single parameter, which is clearly described as 'The customer external unique identifier (from your application).' The description echoes this by mentioning 'by external id', but does not add new insight or format details. Baseline 3 is appropriate when the schema fully handles parameters.

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 clearly states the action ('Retrieve'), the resource ('a single customer'), and the key identifier ('by external id'). It also references the API endpoint, leaving no ambiguity about what the tool does. This distinguishes it effectively from siblings like lago_list_customers or lago_create_customer.

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 description implies usage for retrieving a specific customer, but it does not explicitly state when to use this tool versus alternatives like lagolist_customers or lago_get_customer_current_usage. No when-not-to-use or exclusion criteria are provided, leaving the agent to infer context.

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