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

Annotations already declare readOnlyHint=true, and the description adds essentially nothing behavioral on top — no auth requirements, no failure modes for an unknown id, and no note on what data comes back. The API endpoint mapping is the only extra detail and it is not behaviorally informative.

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 action, no padding. The trailing 'Polar: GET /v1/customers/{id}' is mild filler but does anchor the tool to its upstream API.

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 this is close to adequate, but with no output schema the description could have said what a customer record contains or what happens for a missing id. It covers the call mechanics but stops short of being fully self-sufficient.

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 fully documented there. The description's 'by Polar id' merely restates the schema, adding no format, syntax, or id-provenance detail beyond it. Baseline 3 is 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 and resource ('Fetch a single customer by Polar id'), which is clearly distinct from the list counterpart polar_list_customers. It does not, however, distinguish itself from the similarly named siblings polar_get_customer_state or polar_get_customer_state_by_external_id.

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 Polar id' implicitly signals when to use this over the by-external-id variant, which is useful. But there is no explicit when-to-use guidance, no prerequisites, and no named alternative, leaving selection largely to inference.

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