get_usage

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

Annotations already indicate readOnlyHint=true and destructiveHint=false, and the description adds valuable context: 'Free of token charges' and details on what it returns. It clarifies the tool's non-consuming nature, going beyond the structured annotations.

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 sentences, front-loaded with purpose, followed by a clear use case and a key behavioral note. No redundant information or filler, making it highly efficient.

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?

Given the tool's simplicity (0 params), the presence of an output schema, and complete annotations, the description covers all necessary aspects: what it does, what it returns, when to use it, and a distinguishing behavioral trait. Nothing is missing.

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 no parameters, and the description correctly doesn't introduce any. Schema coverage is trivially 100%, given the empty schema. The description adds implicit meaning by indicating the 'calling key' is used automatically, aligning with the baseline for zero-parameter tools.

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 opens with a specific verb+resource: 'Check the calling key's remaining token balance and plan capabilities.' It enumerates concrete outputs (monthly allocation, tokens used, tokens remaining, plan capabilities) and distinguishes itself from sibling tools, none of which cover balance/plan status.

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?

It explicitly states when to use: 'Use this to pre-flight a metered call: decide whether enough balance is left before spending.' It doesn't mention alternatives or when-not, but as a unique utility among siblings, this is sufficient.

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