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

No annotations are provided, so the description carries the full behavioral burden. It discloses that the result is a percentage and that the default period is 12, but says nothing about return format, input parsing, edge cases like division by zero or insufficient values, or any other behavioral trait. Thin for a no-annotation tool.

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?

Two concise sentences, front-loaded with the purpose followed by parameter guidance. Minor redundancy in 'Roc:' and 'as a percentage', but no wasted sentences.

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?

A simple two-parameter calculator with no output schema and no annotations. The description covers purpose and parameters but omits return shape (scalar vs array), input format, and error behavior, leaving the agent uncertain about what comes back. Partially complete but not fully adequate without 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 the baseline is 3. The description adds the default period value (12) and frames values as an array, but the schema types both parameters as strings, creating a mismatch without resolving input syntax. Baseline 3 is appropriate.

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 ('Calculate') and resource ('Rate of Change (ROC) as a percentage over a period'), and mentions the default period. However, it does not distinguish this from sibling tools such as x402-rate-of-change or x402-percentage-change, so an agent cannot easily tell which ROC variant to choose. Clear but without sibling differentiation.

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?

Provides no when-to-use guidance, no when-not-to-use conditions, and no alternatives. It only says to provide values and an optional period, which is parameter instruction rather than usage context. Implied usage at best.

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