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

The readOnlyHint annotation already establishes that this is a safe, non-mutating call, so the bar is lower. The description adds the underlying route (GET /brands/{brand_id}/usage) and the exact shape of the credit breakdown, which is genuinely useful context, but it says nothing about auth requirements, caching, or billing-period boundaries.

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?

One front-loaded sentence naming the resource and its returned fields, followed by a short route reference. Every clause carries information; the endpoint path is slightly redundant but still orienting.

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 output schema, the description does the useful work of listing the returned credit fields, and the readOnlyHint covers the safety profile. For a zero-parameter read, an agent has enough to invoke it correctly; only the billing-period semantics remain vague.

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 baseline of 4 applies. Schema coverage is 100% and there is nothing for the description to clarify beyond the fact that the brand context is implicit in the route.

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?

The description names the specific resource (message credits for the current billing period) and enumerates the four values returned (total_credits, credits_used, credits_available, limit), which clearly separates it from every sibling in the list. It never states an explicit verb, relying on the name 'get', so it falls just short of the highest tier.

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?

Usage is only implied – the tool is self-evidently a read-only usage lookup, and no condition, prerequisite, or alternative tool is mentioned. There is no explicit statement of when to call this versus get_analytics or any other reporting sibling.

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