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

Annotations already declare a safe, read-only, idempotent, closed-world operation, so the behavioral bar is lower. The description adds the useful fact that a 12-month projection is optional and driven by expected net-new revenue, but says nothing about output format or how the projection is computed. With annotations carrying the safety profile, this is adequate but thin.

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 first sentence is tight and front-loads the core purpose. The second sentence is an external marketing link that does not help an agent select or invoke the tool, so it dilutes rather than earns its place.

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 three-parameter calculator with full schema coverage, no output schema, and annotations covering the safety profile, the definition supplies enough to call the tool correctly. It stops short of explaining what the returned ARR/projection looks like, which is a minor omission given the lack of an output schema.

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 all three parameters are already fully documented in the schema. The description's phrase 'expected net-new monthly revenue' loosely paraphrases the expansion/new-business and churn parameters but adds no syntax, sign convention, or default information beyond the schema. 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?

States a specific verb and resource ('Annualize MRR into ARR') plus an optional projection mode, so the core operation is unambiguous. It does not differentiate itself from related siblings such as arr_multiple_calculator, mrr_bridge_planner, or net_revenue_retention_forecaster, so an agent must infer which annualization/forecast tool fits.

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 names no when-to-use condition, no prerequisites, and no alternative. With many overlapping revenue-metric siblings in the list, the absence of any routing guidance is a real gap. Use is only weakly implied by the tool name.

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