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

The description discloses multiple behaviors beyond annotations: rounding remainder to final payment, error handling ('never raises a protocol error — it returns {"error": ...}'), and the consequence of read-only and idempotent semantics ('so after correcting the input it is always safe to retry'). Annotations already declare readOnlyHint and idempotentHint, but the description adds practical retry guidance. No contradictions with annotations.

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 well-structured with a clear logical flow: purpose, rounding behavior, example, usage guidelines, error handling, and idempotent note. Every sentence adds meaningful information. While it is not excessively verbose, it could be slightly more concise (e.g., the 'PREMIUM (license)' note might be merged). Overall, it is efficient and front-loaded.

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 tool has 3 parameters (100% schema coverage), an output schema, and clear annotations, the description covers all critical aspects: purpose, behavior, usage boundaries, error handling, and retry safety. The example effectively demonstrates the output shape. No significant gaps are present, making the description complete for agent selection and invocation.

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% with clear descriptions for each parameter. The description adds value by providing a concrete example ('Typical input {"total": 1000, "installments": 3, "deposit_pct": 10} returns ...') that illustrates how parameters map to input and output. It also explains the rounding behavior affecting the total. This goes beyond the schema, earning a score above baseline 3.

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 tool's purpose: 'Split a total into an installment schedule with optional deposit.' It uses a specific verb ('Split') and resource ('total into an installment schedule'), and directly contrasts with the sibling 'proration' by stating 'Not for partial-period adjustments (proration).' This effectively distinguishes the tool from at least one sibling, making purpose differentiation clear.

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 explicit when-to-use guidance: 'Use when one total is paid across scheduled dates.' It also gives a clear when-not-to-use scenario: 'Not for partial-period adjustments (proration),' which directly references a sibling tool as an alternative. Additionally, the note 'PREMIUM (license)' hints at licensing constraints, adding further context for agent decision-making.

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