Subscription usage

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

With no annotations, the description carries the burden of disclosing behavior. 'Never cached' is a key behavioral trait, indicating that the tool always returns fresh data. It also implicitly suggests the call is lightweight (hence useful before expensive operations). However, it doesn't explicitly state read-only status or response format, but for a simple usage check, this is adequate.

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 two concise sentences. The first sentence states the purpose, and the second provides behavioral and usage context. No unnecessary words, front-loaded with the core purpose. Every sentence 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?

For a simple tool with no parameters and no output schema, this description is nearly complete. It explains the data (current usage vs. plan limit), the freshness guarantee (never cached), and a practical usage scenario. It lacks an explicit response structure, but the description implies 'usage and limit' sufficiently. Given the simplicity, this is a complete and helpful description.

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 has zero parameters, and the schema is empty (100% coverage). The description adds meaning by explaining what the returned data represents (usage vs. limit), which goes beyond the schema. Since there are no params to document, the baseline of 4 applies, and the description fully compensates for the lack of schema detail.

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 clearly states the tool's function: 'Current API units usage against the plan limit.' This specifies the exact resource (API units usage) and the comparison (against plan limit), distinguishing it from all sibling tools that focus on keyword or site metrics.

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 provides a clear use case: 'Check before running expensive batches.' This tells the agent when to invoke the tool. While it doesn't explicitly name an alternative to avoid, the guidance is actionable and context-specific. It could be improved by noting that for other usage-related queries, other tools might exist, but no such alternative is present.

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