Update expense

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

The annotations already declare this as a destructive, idempotent, open-world mutation. The description adds non-obvious behavioral context: partial updates, proportional share rescaling when cost changes alone, redistribution via split, payer changes via paid_by, and the recommended read-before-update flow.

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 short sentences are front-loaded with the core behavior and parameter consequences. Every sentence provides useful guidance without unnecessary repetition.

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 an eight-parameter mutation tool with no output schema, the description covers the key side effects, prerequisite read, and update semantics. It leaves return-value details and some less risky fields to the schema, which is adequate but not exhaustive.

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 description coverage is high at 88%, so the schema carries most parameter detail. The description still adds meaningful cross-parameter semantics not captured in individual schema fields, especially that changing cost alone rescales shares and that split or paid_by must be used to redistribute or change the payer.

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 verb and resource: 'Edits an existing expense.' The word 'existing' distinguishes it from create_expense and delete_expense, and 'Only the fields you pass change' clarifies the update scope.

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 explicitly tells the agent to 'Read the expense with get_expense first so you can confirm the change with the user,' which is a clear prerequisite. It also explains when to pass split versus paid_by, though it does not state explicit exclusions or when not to use this tool.

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