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

Annotations already cover read-only, idempotent, non-destructive, and closed-world behavior, but the description adds meaningful context beyond them: the call is free, takes no arguments, and returns a specific set of plan, balance, and usage fields. It also clarifies the relationship to per-call lookups_charged reporting in other tools.

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 description is front-loaded with purpose and usage context, then provides output details because no output schema exists. Every sentence contributes: the sibling comparison, the example use cases, the output field list, the cost note, and the no-argument confirmation all help the agent invoke the tool correctly.

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?

There is no output schema, so the description carries the burden of explaining return values, and it does so in detail: account_id, plan, limits, balance, used_today, and 30-day usage. Combined with the annotations covering safety and the explicit no-argument statement, the description is complete for this tool.

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 has zero parameters and the schema coverage is 100%. The description confirms 'Takes no arguments,' which aligns with the schema and removes ambiguity. With no parameters to explain, this hits the baseline 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 a specific verb and resource: 'Get the caller's plan, its limits and the lookups left.' It also distinguishes this tool from siblings by noting 'Other tools report lookups_charged per call; this shows the totals,' so an agent can tell it apart from fetch_batch, parcel_search, and start_run without opening the schema.

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?

It gives concrete usage context, naming sibling tools: check whether 'a large fetch_batch, parcel_search page or start_run fits the remaining balance.' That is clearer than most definitions, though it does not explicitly state when not to use this tool or list exclusions.

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