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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent, closed-world mutation. The description adds valuable behavior beyond that: tax is split unless excluded, negative amounts are refunds, a receipt can be attached, and the call costs $0.01 but is free on failure. It does not discuss permissions or post-creation mutation behavior, so it is strong but not exhaustive.

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 dense but compact, front-loads the core operation, and then layers in the important special cases. Every sentence carries actionable information, with no filler.

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?

For a 15-parameter mutation tool with no output schema, the description supplies enough context on the complex parts—account, paid_from, paid_by, tax, amount, receipt, and cost—to call it correctly in common cases. Some optional parameters and return behavior are left to the schema, but the essential semantics are covered.

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 73%, so the schema already documents most parameters. The description adds real semantic value for the trickiest fields: what account means, the paid_from versus paid_by distinction, tax splitting, amount_includes_tax behavior, and negative amount as refund. It does not add meaning for tracking, rate/currency, or several optional fields, but it covers the main ambiguity.

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 opens with a specific verb and resource ('Book a cost the business paid') and immediately disambiguates account versus paid_from. It also names the expense-claim variant and the sibling tool used to settle claims, so an agent can distinguish this from siblings like books_record_entry.

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 clearly states the core usage context and explains when paid_by should be used instead of paid_from, including that the result becomes an expense claim repayable via books_repay_claims. It lacks an explicit comparison against books_record_entry or other entry-creation paths, but the main usage branches are covered.

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