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

Beyond the readOnly hint, the description explains the key behavioral nuance: despite the POST verb, the tool 'reads rather than writes,' and that the rate-limit state is 'shared across all callers.' This is exactly the kind of non-obvious behavioral context annotations alone would not convey.

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?

Three concise sentences, each carrying distinct value: the core output, the POST-read caveat, and the shared-limit warning, plus the reactive usage trigger. No filler or repetition of structured fields.

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 parameterless tool with an existing output schema and read-only annotations, the description fully covers purpose, behavior, and when to call it. Nothing needed to safely invoke the tool 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?

There are zero parameters, and schema description coverage is 100%, so no additional parameter semantics are needed. The description adds context about resource scope and side effects rather than parameters, which is appropriate for a zero-argument tool.

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 exactly what the tool provides: 'Current API usage and rate-limit state for the Apollo key in use: consumption per window and how much headroom is left.' It also disambiguates from the many POST siblings by explicitly noting that 'Despite being a POST this reads rather than writes.' The verb/resource pairing is clear and no sibling offers the same function.

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 adds meaningful behavior beyond the annotations: it clarifies the POST semantic mismatch, notes the shared shared-account limits and their cross-caller impact ('one caller exhausting a window affects everyone'). The annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, and the description does not contradict any of them.

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