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

readOnlyHint=true already tells the agent this is a safe read, and the description adds the useful upstream mapping (GET /v1/customers/{id}) and confirms single-record scope. It discloses nothing further about pagination, error behavior, or authentication, so it adds modest value on top of annotations.

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, front-loaded sentences with no filler; the verb and lookup key come first. The trailing 'Polar: GET /v1/customers/{id}' is largely restated by the schema path, keeping it just short of maximal efficiency.

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 whose annotations cover the safety profile, this is essentially complete. The only missing element is any hint about the returned customer payload, which matters slightly more 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 a single well-documented customer_id, so the schema carries the parameter burden. The description's 'by Polar id' and the path template add only marginal confirmation, which is the expected baseline.

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 (fetch) and resource (a single customer) keyed by Polar id, which cleanly separates it from the list-family sibling polar_list_customers. It does not distinguish itself from polar_get_customer_state or polar_get_customer_state_by_external_id, so an agent must infer that from the schemas.

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 only implies usage via 'by Polar id'; it gives no explicit when-to-use, no prerequisite (e.g. you must already hold a Polar customer id), and names no alternative such as the state or external-id lookups. Guidance is left entirely to inference.

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