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

With no annotations and no output schema, the description carries full responsibility for explaining behavior. It states the calculation and required inputs, but does not disclose the output format, how the input arrays should be ordered, whether the arrays must be equal length, or how edge cases are handled.

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 one concise sentence that front-loads the tool's purpose and immediately states the required inputs. There is no filler or repetition.

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 tool with no parameter schema, no annotations, and no output schema, the description is too sparse for reliable invocation. It doesn't explain how the arrays should be passed, what the return value looks like, or any constraints on the input data, so an agent would have to guess at operational details.

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 input schema has zero parameters, so the baseline is 4. The description compensates by explicitly identifying the needed inputs: 'close price and volume arrays.' It does not provide formal parameter names or serialization details, but it adds critical meaning beyond the empty schema.

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 names a specific verb and resource: 'Calculate On-Balance Volume (OBV)' and defines it as a 'volume-based momentum indicator.' This makes the tool clearly distinct from price-only siblings like x402-rsi or x402-ema, and tells an agent exactly what it computes.

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 implies usage: use this tool when OBV must be calculated, especially since it explicitly says to provide close price and volume arrays. However, it does not state when not to use it, mention prerequisites such as array length or ordering, or compare it to any alternative indicator tools.

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