Check plan usage

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds value beyond them by telling the agent what information is returned and when in a workflow to invoke it, which is the useful behavioral context for a no-arg read tool.

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 zero filler: the first states what is returned, the second states when to call it. The most actionable content (what you get) is front-loaded.

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, read-only, non-destructive lookup with no output schema, the description covers what the agent needs: the returned fields and the workflow moment to call it. Nothing material 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 takes zero parameters and the schema has 100% description coverage, so the baseline of 4 applies. The description correctly does not invent parameter semantics that do not exist.

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?

States a specific verb ('Check') and enumerates the exact resources returned: the plan, API credits used and remaining, and the billing period. No sibling in the list (analyze_website, get_report, list_domains, etc.) overlaps with billing/usage, so no differentiation is strictly needed, but the description never names or rules out an alternative.

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?

Gives an explicit proactive trigger: 'Call before a batch of scans.' That is real when-to-use guidance rather than a generic 'use this to check usage.' It stops short of 5 because it names no alternatives or when-not-to-call condition, though none of the siblings plausibly compete.

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