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

Annotations already cover read-only, idempotent and non-destructive, so restating those adds little. The description still contributes real context: it discloses that errors never surface as protocol errors but return {"error": ...}, gives an example message, and notes which output fields are conditional on cac. Only the repetition of annotation-supplied safety hints keeps it from a 5.

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?

Front-loaded with purpose, then concrete input/output example, then usage, then error semantics — a sensible ordering with no filler sentences. The error paragraph is a touch long but each clause carries operational value for retry decisions.

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?

Covers everything an agent needs for a 6-parameter calculation tool: typical call shape, conditional outputs, exclusions, and non-obvious failure semantics. An output schema exists, and the description appropriately summarizes rather than re-specifying return values.

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% and the schema already documents each field including the cac>0, fixed_costs_monthly>0 gating rules. The description's example input shows a typical combination, which is mildly useful, but the "LTV fields appear when cac is provided" note duplicates the schema's own wording. 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?

Specific verb plus resource ("Calculate unit economics") followed by the exact outputs it produces: margin, break-even, LTV:CAC. It also names the two sibling tools it is not (cash_runway, target_price), so the agent can route without opening schemas.

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?

Explicit positive condition ("Use when price, variable cost, and fixed costs are known and margin or break-even is the question") plus two explicit exclusions with the correct alternative named for each. When/when-not/alternatives are all present.

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