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

Annotations cover the safety profile (readOnly, non-destructive), so the description's job is to add substance, and it does: it clarifies the values are actual billed amounts from the ledger, not estimates, and enumerates the cost components (voices, boards, replacements). It stops short of noting freshness or reconciliation behavior.

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 dense sentence with the key qualifier ('actual billed', contrasting with estimates) front-loaded. Nothing wasted and nothing padded.

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 does some of the return-value work by naming the breakdown dimensions and line items. But it omits cost units/currency, aggregation granularity, and the meaning of series_id, leaving gaps an agent would hit on first call.

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 0%, so the description must carry the lone parameter, and it never mentions series_id or its format. The phrase 'by phase and episode' hints at the grouping but leaves the single required identifier entirely undocumented.

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?

States a specific resource and scope: actual billed credits from the ledger, broken out by phase and episode. An agent can distinguish this from cost-adjacent siblings like quote, though the description never names 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?

The description says what the data is but not when to reach for it versus alternatives such as quote/quote_ugc (estimates) or get_account (billing). No prerequisites or exclusions are stated.

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