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

The readOnlyHint annotation already establishes this is a safe read operation. The description adds that the returned value is a billing portal URL and maps it to the REST endpoint, which is useful since there is no output schema, but it doesn't mention auth, expiry, or whether the URL is idempotent or generated per call.

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 compact sentences, front-loaded with the purpose, followed by the API mapping. Zero filler or redundancy.

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 single-parameter read tool with annotations covering the safety profile, the description is nearly complete. The main residual gap is absence of any hint about what the returned URL contains or how long it remains valid, which matters given there is no output schema.

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% with only one required parameter, so the schema already documents external_customer_id fully. The path template restates the parameter but adds no format or semantic detail beyond it, making the baseline 3 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?

States a specific verb (Get) and resource (customer's billing portal URL), which is clearly distinct from siblings like lago_get_customer or lago_get_invoice. However, it does not explicitly name which sibling it differs from or how, leaving differentiation to inference.

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 only implied — an agent can guess this is for generating a portal link for a customer, but there is no when-to-use vs. when-not, no mention of prerequisites, and no reference to alternatives such as lago_get_customer.

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