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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description contributes additional context beyond the annotations: it discloses an authorization prerequisite ('requires read scope') and characterizes the payload as both limits and current counts, which tells the agent what kind of data comes back without an output schema.

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 waste; the functional statement is front-loaded and the auth requirement follows as a secondary constraint. Nothing is repeated from the title or annotations.

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?

For a zero-argument read-only lookup with annotations covering the safety profile, the description supplies everything needed: what is measured, the time boundary (billing period), the required scope, and the shape of the result. No output schema exists, but the description names the two things returned (limits and counts), which is sufficient here.

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 explain and the baseline of 4 applies. The description correctly adds no parameter discussion, instead spending its words on scope and return content.

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 states a specific verb and resource: retrieve contact usage limits plus current counts, scoped to the billing period. The 'contact' qualifier distinguishes it from siblings such as get_ai_usage, get_campaign_usage, and get_usage, though it never names those alternatives 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?

Usage is implied by the narrow scope ('contact usage', 'billing period'), so an agent can infer this is for checking quota consumption rather than general account usage. However, there is no explicit statement of when to prefer this over get_usage or get_ai_usage, and no exclusions or prerequisites beyond the scope requirement.

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