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

With readOnlyHint=true already covering safety, the description adds useful behavioral context: it identifies the brand as belonging to the API key and enumerates the data returned, including registration, opt-in, inbox, and credit-limit details. It does not cover error behavior or rate limits, but those are less critical for this read-only lookup.

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?

The description is front-loaded with the core action and resource, then succinctly lists the returned fields and the brand-scoping context. The trailing endpoint note is compact and no sentence is wasted.

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 carries the return-value burden. It enumerates the key fields the agent can expect, explains that the result is the API key's brand, and clarifies that all other tools operate within that brand.

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 there is no parameter semantics to document. The baseline for zero-parameter tools is 4.

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 names the specific resource (the brand for the current API key) and enumerates the returned fields, making the operation unmistakable. It also distinguishes the tool by noting that every other tool works within this brand, which helps separate it from sibling get/list operations.

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 gives clear context: this returns the brand scoping the API key, and all other tools operate within that brand. However, it does not explicitly state when to call it versus other discovery or settings tools, nor does it list exclusions.

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