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

Annotations already declare readOnlyHint=true, openWorldHint=false, and destructiveHint=false, so the safety profile is covered. The description adds genuine behavior beyond the schema by declaring the return contents (each person's share, tip, effective tip rate, collected total) — valuable since there is 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, zero filler, with the core operation front-loaded and the return payload following. Every clause 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?

With no output schema, the description usefully enumerates what is returned, and the inputs are fully covered by the schema and annotations. It stops short of clarifying edge-case behavior (how rounding remainders are absorbed, whether tipOnTax defaults to false), which keeps it from a 5.

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%, so the schema already documents all six parameters including the enum values for roundMode and the boolean tipOnTax. The description only echoes 'tax, tip, and optional rounding' and adds no syntax or default-value detail beyond the schema, so the baseline 3 applies.

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 plus the exact scope: split a bill across a group after tax, tip, and optional rounding. This is unambiguous and cannot be confused with any of the sibling calculators (mortgage, bmi, percentage, etc.).

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 condition 'split a bill across a group' implies when to use it, but there is no explicit guidance on when not to use it, no prerequisites, and no named alternative. For a single-purpose calculator with no competing sibling, implied usage is adequate but nothing more.

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