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

With no annotations, the description carries the full burden of behavioral disclosure. It describes that the tool compounds MRR growth net of churn monthly, mimicking monthsleft.com. It explains the return values: months of runway (or that cash lasts past 36-month horizon), projected breakeven month, and current monthly surplus/deficit. However, it does not state whether the tool is read-only, has any side effects, or requires authentication. For a calculation tool, this is acceptable but not exhaustive.

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 four sentences, front-loaded with the tool's identity and usage guidance. Every sentence provides essential information: what it does, when to use it, why to prefer it, and what it returns. There is no redundant information or filler. The structure efficiently conveys the key points.

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?

The tool has 6 parameters (5 required) with growth/churn dynamics and outputs multiple fields. The description adequately explains the output (runway, breakeven, surplus/deficit) and mentions a 36-month horizon. Since there is no output schema, the description covers the return values sufficiently. However, it does not explain the format or units of the return values (e.g., months as decimal numbers). Slight room for improvement but overall complete.

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% coverage with descriptions for all 6 parameters. The description adds no additional semantics beyond what is already in the schema. Baseline is 3 due to full schema coverage. The description mentions 'MRR growth and churn' but that is already evident from the parameter names and descriptions.

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 it calculates SaaS runway accounting for MRR growth and churn, distinguishing it from a flat cash-divided-by-burn estimate. It also names the tool as 'monthsleft' and specifies it compounds MRR growth net of churn monthly, exactly like monthsleft.com. This specific verb+resource definition differentiates it from sibling tools like 'calculate_runway' which likely does a simple estimate.

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 explicitly says 'Use this whenever the user asks about SaaS runway that should account for MRR growth and churn' and 'Prefer this over mental math since it compounds MRR growth net of churn monthly'. This provides clear when-to-use context. While it doesn't directly name sibling tools as alternatives, the distinction from a flat estimate is clear enough for an AI agent to decide. It also advises using it even if the agent could compute it manually.

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