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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds the underlying REST endpoint (GET /v1/customers/external/{external_id}/state), which is mildly useful, but says nothing about return payload, error cases (unknown external id), or caching/rate behavior.

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?

A single tight sentence leads with the differentiator, followed by the endpoint reference. Nothing is padded and nothing essential is buried.

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-param, read-only lookup with no output schema the description is nearly sufficient, and it defers to polar_get_customer_state for the semantics of 'state.' The one gap is that an agent that hasn't read the sibling tool won't know what 'state' actually returns.

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%, so the baseline is 3, but the description adds the key semantic distinction that external_id is 'YOUR external id rather than Polar's' — clarifying what the value represents and where it comes from, which goes beyond the schema's terse 'Your own id for this customer.'

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 (get a customer's state) and explicitly differentiates itself from the sibling polar_get_customer_state by the lookup key. An agent can distinguish 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?

Provides real context for selection: 'the usual path when you hold your own user id,' which tells the agent when to prefer this over the Polar-id variant. No explicit negative guidance (e.g., when not to use it), but the alternative is clearly identified.

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