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

With no annotations, the description carries the full burden. It does add genuinely behavioral context the schema cannot express — the free-trial quota of 5 calls per signed wallet — but omits how arrays are encoded (the schema types are strings), whether the two arrays must be equal length, and what the response looks like.

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 definition is short and front-loads the computation before the input hint and the quota note. The promotional emoji line is tolerable but is the one sentence that does not help an agent invoke the tool correctly.

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 three-parameter tool with no annotations, no output schema, and zero schema description coverage, the description should explain the array encoding and the unexplained "values" parameter. Neither is covered, leaving real ambiguity an agent cannot resolve from structured fields.

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 0%, so the description must compensate and it only partially does: it names close price and volume, mapping to two of the three parameters, but the third parameter "values" is never mentioned and remains completely undefined. The mismatch between "arrays" in the description and string-typed properties is also left unexplained.

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?

"Calculate On-Balance Volume (OBV), a volume-based momentum indicator" gives a specific verb plus resource and even defines the acronym and indicator family, so an agent knows exactly what computation happens. It does not explicitly distinguish itself from adjacent indicator siblings such as x402-momentum, x402-sma, or x402-volume, which keeps it short of a 5.

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 line "Provide close price and volume arrays" tells the agent what input shape is expected, which implies usage, but there is no statement of when to prefer OBV over sibling indicators or any precondition/exclusion. Guidance is implied rather than stated.

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