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

Annotations only provide readOnlyHint=false and other false hints, so the description carries the burden of behavioral disclosure. It adds meaningful context: members are matched by name, the user is the default payer, equal split unless amounts are given, and optional account logging. These go beyond the annotations and help the agent understand 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 three sentences, front-loaded with the main purpose, and each sentence adds distinct value: the first states what it does, the second explains matching and payer default, the third explains optional account logging. No waste or redundancy.

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 tool with 10 parameters and an output schema, the description covers the non-obvious semantics (split logic, payer default, account logging) and does not need to describe return values. It omits standard fields like date/note/category but those are self-explanatory, so the description is adequate for correct invocation.

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 60%, so the baseline is 3. The description adds value for split_among (equal split default), paid_by (default you), and account_id (only when you paid), but does not clarify date, note, title, or category_id. It enriches some parameters but does not fully compensate for the uncovered ones.

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 uses a specific verb 'Add' and resource 'expense to a group', and clearly explains the core semantics (who paid, who shares). It distinguishes itself from sibling add_* tools like add_category or add_holding by focusing on group expenses, making the purpose unambiguous.

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 usage for group expenses but does not explicitly mention alternatives or exclusions. It does not say, for example, to use log_transaction for non-group expenses or add_planned_expense for future ones, leaving the agent to infer the appropriate context.

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