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

Without annotations, the description carries the burden. It discloses that figures are computed live from the catalogue and reproducible, and notes 'Claims no return' — meaning it offers only a threshold, not a recommendation. This gives useful behavioral context beyond a simple read-only calculation.

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 sentences, each adding essential information: headline 'Free:', what it computes, and when to call it. The phrase 'Claims no return' is slightly ambiguous but still concise. Overall compact and front-loaded with the most important detail.

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?

Despite having no output schema, the description explains the conceptual output ('threshold') but not the exact return structure or data format. As a simple zero-parameter tool, the essential context is covered, but clarity about what the response contains would improve completeness.

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 tool has zero parameters, so the baseline of 4 applies. The description doesn't need to explain parameters since there are none, and the schema is already fully covered.

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 the tool provides the acquisition cost and break-even probability threshold, using specific language like 'cost to acquire in full' and 'break-even probability.' It is distinct from sibling tools like buy_exclusive or how_to_pay, which focus on purchasing/payment rather than economic analysis.

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?

Explicitly says 'Call this before deciding whether to spend,' providing a clear situational trigger. However, it does not explicitly name alternatives or mention when not to use it, though the context is strong enough to differentiate it from siblings.

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