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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description contributes only 'Costs nothing,' confirming no charge/side effect. It adds little behavioral context beyond what the structured annotations provide.

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?

The first sentence is a run-on mixing four separate outputs, and the remaining five sentences are pricing and abuse-prevention policy that does not help select or invoke the tool. It is padded and not front-loaded around the tool's actual function.

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 no-param, read-only tool with an output schema that documents return values, the description is functionally adequate. However, it spends its length on pricing policy rather than the usage/reset/limit semantics an agent would want when reading quota state.

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 there is nothing to document and the baseline is 4. The parenthetical 'under unit_packs' hints at structure but no actual parameter exists to clarify.

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 opening clause specifies the resource precisely: units used and left, when they reset, every limit, and units remaining in unit packs. An agent can tell this reads account usage/limit state. It never explicitly distinguishes itself from the sibling `subscription`, so it stops short of a 5.

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?

There is no statement of when to call this versus `subscription` (which likely handles plan management). The mention of 'under unit_packs' reads like policy prose rather than routing guidance. The body is plan/pricing narrative, not usage instruction.

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