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

Annotations already cover safety (readOnlyHint, idempotentHint, destructiveHint=false), so the description's value is in the extras it supplies: it discloses the return payload (tip amount and total including tip) and a per-call cost of 1 credit, neither of which appears in the annotations. It does not address rounding behavior or how string inputs are coerced, which are the remaining behavioral unknowns.

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 front-loaded sentences plus a parenthetical cost note; every clause carries information (what it computes, what it returns, what it costs) and there is no filler 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 two-parameter arithmetic tool with full schema documentation and complete safety annotations, the definition is nearly sufficient — it even covers the return values despite there being no output schema. Minor gaps remain around rounding/precision and negative or zero inputs, which matter for a money calculation.

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%, with bill_amount and tip_percentage fully documented including units and the "15 = 15%" convention. The description restates the two inputs ("bill total and tip percentage") without adding format, rounding, or range detail, so the schema does the heavy lifting and the baseline of 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 names a specific verb and resource ("Calculates the tip amount") and states the two inputs it consumes, so the agent can tell this apart from siblings like calculate_tax or calculate_discount on subject matter alone. It stops short of explicitly contrasting with those nearest alternatives.

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 only implied: the domain (tipping) makes the intended scenario obvious, but there is no statement of when to prefer this over calculate_tax, calculate_discount, or the generic calculate tool. No prerequisites or exclusions are given.

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