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

Annotations already indicate it's not read-only, not destructive, and idempotent. The description merely says 'updates' without elaborating on permissions, side effects, or constraints (e.g., whether missing fields are reset). No contradiction with annotations, but the description adds no behavioral context beyond the obvious.

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 concise sentence with no fluff. It conveys the essential action efficiently. However, it could include a brief mention of typical use without significantly increasing length.

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 complexity (5 parameters, nested objects) and the presence of an output schema, the description is too minimal. It does not explain the update semantics (e.g., full replacement vs partial update), nor does it address prerequisites or output expectations. The output schema may cover return values, but the description should at least hint at the scope of the update.

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%: all 5 parameters have detailed descriptions in the input schema. The tool description adds no extra meaning beyond what's already documented structurally, so a baseline score of 3 is appropriate.

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 verb 'updates' and the resource 'existing bill', effectively communicating the tool's primary action. It distinguishes from sibling tools like create_bill (create new) and set_bill_selections_batch (batch operations on selections). However, it could be more specific about which bill attributes are modifiable, as implied by the input schema.

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 provides no guidance on when to use this tool versus its siblings. It does not specify prerequisites (e.g., bill must exist) or alternative tools for different scenarios. The sibling list includes create_bill and set_bill_selections_batch, but no explanation of trade-offs is given.

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