check_usage

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

With no annotations, the description carries the full disclosure burden, and it covers both the mechanism ('headless /cost call') and the side effect ('persist it to USAGE_STATE_PATH'). It could add more about failure behavior or prerequisites, but the core behavioral traits are disclosed.

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?

Single sentence, front-loaded with the primary purpose, and every clause earns its place by adding scope, mechanism, or persistence detail. No redundant text.

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-parameter probe with an output schema, the description covers purpose, scope, mechanism, and persistence. The main gap is the absence of any note about when not to call it or what the persisted state is used for, but this is minor given the low complexity.

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 description isn't required to add parameter-level meaning; the baseline for zero-param tools is 4. The description's mention of scope is not parameter documentation but it reinforces what the tool measures.

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 a specific action ('Probe'), a concrete resource ('current subscription usage'), and a precise scope ('current session + current week'). This distinguishes it from the unrelated sibling tools and leaves no doubt about what the tool does.

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 makes the invocation context clear: an agent calls this tool when it needs current subscription usage, scoped to session and week. It doesn't name explicit exclusions or alternatives, but no sibling tool overlaps with this usage-checking function.

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