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

Annotations already declare readOnlyHint and idempotentHint, so 'Read-only' is partly redundant. What earns credit is the disclosure of the auth model ('Requires a per-customer API key') and the fixed 30-day window, which the annotations do not cover.

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?

One sentence, front-loaded with the returned data, then two short clauses for scope, safety and auth. Every clause carries information; nothing is padding.

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 correctly summarizes the return payload (balance, unit price, 30-day usage), which is what the agent needs. Minor gaps: no mention of what happens without a valid key or whether the 30-day window is fixed or configurable.

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; baseline 4 applies. The description correctly leaves out any parameter discussion rather than inventing one.

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?

Uses a specific verb+resource ('get the prepaid credit balance, price per document, and the last 30 days of usage') and scopes it to 'the account that owns the API key'. This is unambiguously distinct from the extraction/bulk siblings without needing to name them.

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?

Usage is only implied: the description states the account scope but never says when to call this (e.g., before submitting bulk extraction to check credit, or to monitor spend). No alternatives are named, though there is little overlap with extract_sds/get_bulk_job.

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