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

Annotations already indicate readOnlyHint=true and idempotentHint=true, but the description goes further by disclosing error handling behavior ('never raises a protocol error — it returns {"error": ...}') and explicitly stating that every call is read-only and idempotent, making retries safe. It also explains conditional behavior (LTV fields appear when cac is provided). This adds substantial context beyond annotations, with no contradictions.

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: it opens with a one-line purpose, provides an illustrative example, then gives usage guidance, error behavior, and a safety note. Every sentence contributes useful information with no redundant content. Minor 'FREE' note is harmless and does not detract from conciseness.

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?

Despite having an output schema (which reduces the need to explain return values), the description still covers key invocation context: typical input/output, when to use vs alternatives, error handling format, and idempotency/read-only safety. It is complete for an agent to select and correctly invoke this tool.

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?

The input schema has 100% description coverage, so the baseline is 3. The description adds a concrete typical input/output example that maps parameters to results, and clarifies conditional parameter effects (e.g., fixed_costs_monthly enables break-even, cac enables LTV). This extra help justifies a 4, though the schema already covers meaning well.

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 function with a specific verb and resource: 'Calculate unit economics: margin, break-even, LTV:CAC, and a plain reading.' It also distinguishes itself from siblings by explicitly saying what it is not for (cash_runway, target_price). This provides excellent purpose clarity and differentiation.

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 guidance is explicit: 'Use when price, variable cost, and fixed costs are known and margin or break-even is the question. Not for cash position over time (cash_runway) and not for solving backward from a target margin (target_price).' This not only states when to use but also names alternative tools and when not to use them, which is exactly what the dimension requires.

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