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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely non-obvious context — the 1-credit cost — but says nothing about rounding behavior, currency handling, or how per-person shares are derived. With annotations carrying the safety burden and output schema carrying returns, a 3 is appropriate.

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, front-loaded with the purpose and ending with the credit cost where it is easy to find. The redundant 'Tip Calculator: Tip Calculator computes' opening wastes a few tokens but the rest is entirely informative.

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?

This is a low-complexity calculation tool with an output schema and full parameter coverage, so the description need not explain return values or edge cases in depth. Inputs, outputs, and cost are all present; only edge-case behavior (rounding, invalid group size) is absent, which is minor here.

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 all four parameters (amount, people, percentage, currency) are already fully documented with types, defaults, and examples. The description restates the same three inputs without adding format guidance 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?

The description states a specific verb and resource ('computes tips and splits bill totals across group members') and enumerates the outputs (tip total, overall cost, per-person shares). An agent can tell this apart from siblings like MathCalculator or LoanCalculator on intent alone. It does not explicitly contrast itself with a sibling, so it stops just short of a 5.

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?

Usage is implied by the stated inputs ('Pass a pre-tip bill amount, tip percentage, and group size'), which is enough to know when the tool fits. There is no explicit when-not guidance or named alternative for plain arithmetic or percentage math, leaving that inference to the agent.

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