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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is free. The description adds genuinely new traits: results are newest-first, the default window is 24 hours, and the call itself is free ('Free to call'). It does not mention the result cap/pagination behavior beyond the schema's `limit`, which keeps it 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?

The core payload is front-loaded in the first clause, and the closing two sentences handle scope and the alternative. The middle of the first sentence is a long comma-chained list of return fields, which is dense but each item is informative.

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 return-value burden — and it does: per-charge breakdown, aggregate totals, current token balance, and per-token value. For a two-optional-param read tool with full annotation coverage, nothing an agent needs to call it correctly is missing.

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?

Schema coverage is 100% with both parameters well documented (ranges and defaults), so the baseline of 3 applies. The description restates the `hours` default but says nothing about `limit`, adding no syntax or semantics beyond the schema.

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?

Opens with a specific verb+resource ('What your calls cost: every charge on this account') and enumerates the returned fields — what it was for, model, tokens, dollar value — plus totals and balance. It also names the sibling it is not (check_balance), so an agent can distinguish it 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?

Explicit routing: 'Use this to itemize Seed Audio, Sync 3 lip-sync, generate_sound and every video or picture call' tells the agent which upstream generation tools this reconciles. 'For just how many tokens are left, use check_balance' gives the negative case and the exact alternative.

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