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

Annotations only indicate non-read, non-destructive, and non-idempotent behavior; the description adds meaningful defaults ('paid_by defaults to the person you act for; split_among defaults to everyone') and the mandatory confirm-before-call behavior. It does not mention response/return behavior, but this is less critical for a mutation with no output schema.

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 with no filler; the core action and equal-split behavior are front-loaded, and the confirmation requirement is stated in one compact final sentence.

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 7-parameter mutation with no output schema, the description covers the essential behavior, defaults, and the required user confirmation, while the schema handles parameter-level detail. It could be slightly stronger by distinguishing itself from record_payment, but it is not materially incomplete.

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%, so all parameters are already documented with descriptions. The description reinforces the split_among and paid_by_participant_id defaults and adds the 'person you act for' nuance, but does not substantially add 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?

Description opens with 'Record a shared expense, split equally,' using a specific verb and object that clearly states the tool's function. Combined with the title 'Add an expense,' it is distinct from siblings like get_expenses (read) and record_payment (payment settlement).

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?

'Record a shared expense' gives clear context for when the tool applies, and the confirmation instruction ('Always confirm the amount and who shares it with the user first') is an explicit pre-call requirement. It does not explicitly name alternatives or exclusions, but the context is clear enough for selection among the listed siblings.

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