update_expense

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

Annotations already declare destructiveHint=true, so the mutation risk is covered. The description adds genuinely useful behavioral context: changing the amount requires also supplying split, and the tool will not guess how to redistribute. It does not mention the confirmation step, though the schema documents the 'confirm' parameter, so this is a minor gap rather than a serious omission.

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?

Two sentences, no filler. The first sentence front-loads the tool's purpose and target fields, and the second explains a critical constraint. Every sentence earns its place.

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?

Given the rich input schema, 100% parameter coverage, and annotations covering safety, the description is nearly complete. It could explicitly mention the confirmation workflow or the destructive nature of updates, but the schema and annotations already carry that information. For an 8-parameter update tool, this is adequate and slightly above the minimum viable bar.

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 100%, so the description has little burden to explain parameters. It does reinforce the amount-requires-split rule, but that rule already appears in the amount parameter's schema description. No additional parameter-level semantics are provided beyond what the schema already offers.

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 ('Update') and a specific resource ('an existing expense'), and enumerates the mutable fields: description, amount, split, date, or category. This makes it immediately distinguishable from sibling tools like create_expense, delete_expense, get_expense, and list_expenses.

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 clearly implies the tool is for modifying an existing expense rather than creating, deleting, or viewing one. It does not explicitly name alternatives or state when not to use it, but the context is clear enough for an agent to choose this tool correctly.

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