add_expense

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

With no annotations, the description must disclose behavioral traits. It does reveal the splitting behavior ('split equally among participants') and a constraint on amount_cents ('positive integer'), but it does not mention that the expense affects group balances, requires permissions, or that the payer must be among participants. These are notable omissions for a mutating tool, leaving the agent to infer side effects.

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 a single sentence with zero filler. It is front-loaded with the core action and includes the key behavioral detail (equal split). Every word adds value, and it is concise without being under-specified in terms of the action.

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 tool has 5 required parameters, no annotations, and an output schema (so return values are covered), the description still omits explanations for group_id and description, and does not mention the effect on balances or any prerequisites. This is incomplete for an agent to correctly invoke the tool without further research, especially for a write operation.

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 0%, so the description must explain all parameters. It only addresses payer, participants, and amount_cents (with a constraint). It does not explain the purpose of group_id or description, nor the relationship between payer and participants. This leaves the agent guessing about two of the five required fields, which is a significant gap.

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 clearly states the action: 'Record an expense paid by `payer`, split equally among `participants`.' This is a specific verb ('record') with a resource ('expense') and the splitting rule, which distinguishes it from sibling tools like delete_expense or add_member. The purpose is unambiguous and not a tautology.

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 implies when to use the tool (when you need to record an expense) but does not explicitly state when not to use it or mention alternatives. It lacks guidance on scenarios like recording a partial split or unequal shares, and does not exclude using it for other purposes. No comparison to siblings is given, though the action itself makes the usage context reasonably clear.

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