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

Annotations already cover readOnly/idempotent/non-destructive, but the description adds material facts beyond them: the call is free and never billed, an API key is required, and results are reported as daily snapshots with total/used/remaining. It does not discuss caching or freshness beyond the 30-day window, so it stops just short of a 5.

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?

Four compact segments — identity/contents, usage triggers, cost, auth requirement — each front-loaded and earning its place. No filler verbs or restatement of the tool name.

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?

With no output schema, the description carries the burden of explaining returns, and it does so (balance, plan, per-endpoint usage, daily snapshot totals). Combined with cost and auth notes, an agent has everything needed to call it and interpret the result.

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?

This tool takes zero parameters, so per the rubric the baseline is 4; there are no arguments whose meaning the description could clarify. The description correctly avoids inventing parameter details.

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 resource (the account) and enumerates exactly what it returns: balance, plan, 30-day usage by endpoint, and product-tracking allowance, plus a REST equivalence (GET /v1/account). No sibling tool covers account-level data, and the naming of the returned fields makes it unmistakable.

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 'USE WHEN' clause gives four concrete trigger questions (credits left, job cost, key usage, tracking room), which is exactly the intent-to-tool mapping an agent needs. It also states the precondition/negative case: 'API key required (keyed lanes); without one, nothing to report.'

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