Check remaining monthly units

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

Annotations only declare read-only/idempotent/non-destructive; the description adds substantial context beyond them: it costs 0 quota units, never touches the paid data provider, reads Vantage's own usage record, and degrades to tier 'unmetered' in stdio/local-dev mode with no HTTP token. This is exactly the operational context an agent needs and could not derive from 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?

Purpose and the zero-cost caveat are front-loaded, followed by the return shape and the sibling cost table. Although long, every sentence serves the agent's decision (whether to spend quota, what comes back), so nothing is filler.

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?

No output schema exists, but the description supplies the full return shape ({tier, period, units_used, units_limit, units_remaining}), the quota-cost table for every sibling, and the stdio-mode edge case. An agent has everything required to call and interpret it.

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 baseline is 4 and there is no schema semantics to elaborate. The description instead documents the return shape, which is useful but not a parameter concern.

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+resource ('Check how much of this billing period's quota is left') and frames the scope precisely. It clearly distinguishes itself from siblings by naming them and their costs, so an agent knows this is the free quota-inspection tool, not a data-consuming analysis tool.

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 explicit when-to-use ('before spending any of it', to answer 'how many checks do I have left', to check whether a batch call will fit) and reinforces the decision with per-sibling cost figures. No inference about when to prefer this tool is left to the agent.

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