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

Goes well beyond the annotations: quantity 0 clears a selection, omitted selections stay unchanged (concretising idempotentHint), selections and the display name are visible to anyone with the bill link (privacy disclosure), and OAuth is required. The only gap is that it doesn't describe error behaviour or what the response confirms, but annotations already cover the safety profile.

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?

Front-loaded with the trigger condition and tightly packed, but slightly long and mildly redundant — the later 'cannot select on behalf of other people' restates the earlier 'do not select for friends'. Every other 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?

An output schema exists, so return values need no explanation, and the description covers trigger, exclusions, mutation semantics, visibility and auth. Nothing an agent needs to invoke this correctly is missing.

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 the baseline is 3, but the description adds real semantics the schema lacks: quantity 0 clears a selection, omitted selections remain unchanged, and IDs must be actual bill/item IDs. That is meaningful behavioural meaning for both parameters rather than a restatement.

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?

States a specific verb and resource: saving absolute item-selection quantities for the connected user on an existing shared bill, explicitly scoped as affecting only that user's personal share. It is readily distinguishable from create_bill, update_bill and get_current_user_profile, and explicitly says it does not change bill items, prices or totals.

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?

Gives an explicit trigger (user asks to select, change or clear their own items on an existing shared bill) and explicit exclusions (not for creating/editing a bill, not for selecting for friends, not for marking payments completed). The alternatives are described functionally so an agent can route correctly without opening sibling schemas.

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