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

readOnlyHint=true already declares the safe-read profile, and the description reinforces it with the underlying GET endpoint. It adds the lookup-key semantic, which is useful, but no additional behavioral detail (not-found behavior, auth scope) beyond 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?

One front-loaded sentence contrasting the two lookup paths, followed by the raw endpoint as a trailing anchor. No filler, and the distinguishing clause comes first.

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 full schema coverage and a readOnlyHint annotation, everything an agent needs is present: purpose, distinguishing condition, parameter meaning, and the underlying API route. No output schema exists, so return-value documentation is not required here.

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 coverage is 100% and only one parameter exists, so the baseline is high. The description still adds real meaning by clarifying external_id means the caller's own id rather than Polar's internal id, disambiguating a plausible confusion.

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+resource ('get a customer's state') and explicitly frames the scope difference from the sibling polar_get_customer_state — lookup is by the caller's external id, not Polar's. An agent can pick between the two without opening either schema.

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?

Names the alternative (polar_get_customer_state) and gives the selection condition: 'the usual path when you hold your own user id.' Clear context for when to use it, though it doesn't state a negative case (e.g., when you only have a Polar id, use the other).

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