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

Annotations already declare readOnlyHint=true, so safety is covered structurally. The description adds real behavioral context beyond that: this is an aggregation call that returns subscriptions, benefits and entitlements in one shot, which matters for planning. It stops short of describing response shape, size or any rate limits.

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 plus an endpoint reference, with the payload contents front-loaded before the value proposition. Every clause carries information; nothing is padding.

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 with a readOnlyHint annotation, the essentials are present, and the description compensates for the missing output schema by naming what comes back. Minor gaps remain around pagination or response size, but an agent has enough to call this correctly.

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?

There is a single parameter and schema description coverage is 100%, so the schema already states that customer_id is the Polar id. The description adds nothing about the parameter (e.g. id format or where to obtain it), so the baseline 3 for schema-documented params applies.

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?

It uses a specific verb (Fetch) plus resource (customer) and enumerates what is returned: active subscriptions, granted benefits and entitlements. That is clearly distinguishable from list tools or polar_get_customer. It does not, however, differentiate itself from the sibling polar_get_customer_state_by_external_id, which is the one tool an agent could easily confuse it with.

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 best answer to what does this customer currently have?' implies a usage scenario, which is helpful framing. But there is no explicit when-not guidance and no routing to alternatives such as polar_get_customer (lighter lookup) or the by-external-id variant, so the agent must infer the choice.

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