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

Annotations declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the agent knows it's a safe, pure calculation. The description adds nothing beyond that—no mention of output format, error behavior, or assumptions. With annotations covering safety, a 2 reflects minimal added behavioral context.

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 a single sentence and a URL. The first sentence is concise and front-loads the key function. However, the URL is extraneous to tool invocation and adds noise. It's adequately sized but not optimally structured for an agent.

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 simple 3-parameter read-only calculator with full schema coverage and no output schema, the description is adequate but minimal. It doesn't explain the output (e.g., what the matrix contains) or assumptions, which could be helpful since there's no output schema. It's minimally 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?

Schema description coverage is 100%, so the schema already documents all three parameters (cpa, spend, decayPct) with clear descriptions. The description doesn't add any parameter-specific semantics beyond what the schema provides. Baseline 3 is appropriate when schema fully covers parameters.

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 states a specific projection task: projecting CPA/CAC inflation at double and triple spend given a decay rate. It's clear what the tool does, but it doesn't distinguish itself from sibling tools (e.g., cpl_cpa_calculator, ltv_cac_calculator) or explain how its output differs from them. No sibling differentiation lowers the score.

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 offers no guidance on when to use this tool versus alternatives like cpl_cpa_calculator or ltv_cac_calculator. It also doesn't state prerequisites or assumptions (e.g., constant decay rate). It merely describes the action without context.

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