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

Annotations already declare readOnlyHint=true, so the safe-read profile is covered. The description adds the underlying GET endpoint as a useful anchor, but says nothing about authentication requirements, rate limiting, or what happens when the id/email is not found. With annotations carrying the safety signal, this is adequate rather than rich.

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 tight clauses: the return payload and accepted identifier forms come first, the API endpoint last. Every element earns its place with no filler.

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?

There is no output schema, so the description compensates by listing the returned fields (email, name, phone, saved instruments), which is exactly what an agent needs. For a one-parameter read-only tool this is close to complete, with only error/not-found behavior left unstated.

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 'id' parameter is fully documented there. The description restates the same 'cus_...' or email formats rather than adding new meaning such as validation rules or fallback behavior when both a customer id and an email exist.

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 details'), enumerates what comes back (email, name, phone, saved instruments), and pins the API endpoint. An agent can distinguish it from checkout_create_customer or the other get_* siblings without opening the 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?

The description implies when the tool applies by naming the two lookup modes (id or email), but it never states when to prefer this over siblings such as checkout_get_instrument or checkout_search_payments, nor any prerequisites. Usage is inferable but not spelled out.

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