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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds a genuinely useful nuance not in annotations: name and email are populated only "when the key belongs to a customer," warning the agent that a partial/null result is possible. It stops short of describing error or auth-failure 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 sentence with no waste, front-loading the resource and the scoping condition (current bearer key) before the conditional return detail.

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?

With no parameters, an output schema present to document the return shape, and annotations covering safety, the description supplies everything an agent needs to select and invoke the tool correctly. The conditional-response caveat is the one extra detail that mattered, and it is included.

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 are zero parameters, so the schema carries nothing to misinterpret and the baseline is 4. The description correctly frames the bearer key as ambient context rather than an argument, matching the empty input schema.

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: returns the authenticated customer for the current bearer API key, plus the fields included (name, email). This clearly distinguishes it from the sibling get_customer, which presumably takes an identifier, though the description never names that alternative explicitly.

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 phrase "for the current bearer API key" implies the when: use it to identify the caller rather than look up an arbitrary customer. However, no alternative sibling (e.g. get_customer) or exclusion condition is named, so the routing guidance is only implied.

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