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 real behavioral context beyond that: the resource is derived from the auth token rather than a parameter, and it names the upstream endpoint (GET /merchant/), signalling a lightweight call. It does not describe error behavior for an invalid token, which is the main remaining gap.

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 with no filler; the return fields are front-loaded and the usage hint and endpoint follow in order of decreasing importance. Every clause earns its place.

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 and no parameters, so the description carries the burden of describing the response, and it does so (business name, email, country, currency). Combined with the documented endpoint, an agent has everything needed to call and interpret this tool.

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?

The tool takes zero parameters, so the 4 baseline applies; the schema is trivially complete at 100% coverage. The description does add the useful nuance that the identity of the merchant comes from the token rather than any argument.

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 (the merchant account) and even enumerates the returned fields (business name, email, country, currency). It also clarifies the scoping — the merchant is the one 'this token belongs to' — which cleanly separates it from the get_customer/get_item sibling reads.

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?

"A cheap way to confirm the token works" gives a concrete primary use case (auth/token validation) rather than leaving the agent to guess. There is no explicit when-not or named alternative, but no sibling performs the same merchant lookup, so the guidance is adequate.

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