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

Annotations already carry the safety profile (readOnlyHint, idempotentHint, non-destructive, closed-world), so the bar is lower, and the description still adds real value: it explains the semantics of the combined score and the 40-point interpretation threshold that no annotation conveys. It does not say whether the returned value is the raw sum or a pass/fail verdict, which keeps it off 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?

Three short sentences, front-loaded with the operation itself, then the interpretation threshold, then the alternative routing and reference link. Nothing is redundant and nothing is buried.

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-input pure calculator with full annotation coverage and a rich schema, the description covers formula, units, interpretation, and alternatives. The only gap is the shape of the return value, which matters slightly more here because there is no output schema to fall back on.

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 both parameters documenting units, sign conventions, and bounds, so the schema already does the heavy lifting. The description's note that profit margin is "usually EBITDA or free cash flow margin" is a modest addition rather than new information, 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 opens with a precise verb-resource statement: it 'adds revenue growth rate and profit margin' into a single score, which is exactly what this calculator does. It also differentiates itself from the sibling burn_multiple by name, so an agent can pick between them without opening either schema.

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?

It gives an explicit alternative route ("Use burn_multiple for capital efficiency instead") plus the interpretive threshold of 40 for a healthy software company, which tells the agent what context this metric belongs to. It stops short of stating the inverse condition — when Rule of 40 is the right choice — leaving that to inference.

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