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

With no annotations, the description carries the behavioral disclosure burden. It discloses the payment cost ($0.03 via x402), the return structure (rate of change with from/to values), and the requirement that field be numeric. It does not mention side effects or limits, but this appears to be a read-only analysis tool, and the disclosed information is significant.

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 concise and well-structured. It front-loads the cost, then defines the purpose, usage guidance, and input hints in a logical flow. Every sentence adds value with no fluff.

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 lacking an output schema, the description explains the return shape (rate of change with from/to values) and gives key constraints. It does not cover all parameters but covers the critical ones. For a moderately complex ranking tool, this is nearly complete, though it could clarify the ranking direction (descending) and default limit behavior.

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 coverage is 0%, so the description must compensate. It adds semantics for 'field' (must be numeric) and 'window_s' (in seconds), but does not explain 'limit', 'dataset', or 'payment_header'. 'limit' and 'payment_header' are less ambiguous given defaults and context, but the coverage is partial, warranting a mid score.

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 precisely states the tool's function: ranking keys by velocity (rate of change) on a numeric field over a window, returning rate of change with from/to values. It clearly distinguishes from siblings by naming anansi_anomalies as the alternative for a different purpose.

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?

Explicit usage guidance is given: 'Use it to find what is moving without reading every series' and 'Do NOT use it to judge whether a move is unusual for that key — that is anansi_anomalies.' This clearly states when and when not to use, with a named alternative.

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