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

With no annotations, the description carries the full burden and does well: it discloses the non-obvious fact that this is a payment-requirement step, that 'no money moves in this call,' and that paying is a separate action. It does not describe failure modes, authentication requirements, or the shape of the returned payment requirement, which a payment-gated tool would ideally cover.

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 tight sentences, front-loaded with the action and the critical caveat about what the call actually returns. The character limit is stated twice (once in prose, once by the schema), which is minor redundancy, but nothing else is wasted.

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 multi-step, payment-gated tool with no output schema, the description supplies the essential sequence and the key behavioral caveat an agent needs to avoid misusing the result. It omits what the payment requirement response looks like and how errors surface, leaving a modest gap.

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?

There is a single parameter with 100% schema description coverage, so the schema already documents the question field and its 800-character limit. The description merely repeats the '<=800 chars' constraint and adds no syntax, format, or content guidance beyond it. Baseline 3 applies.

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 gives a specific verb and resource ('Ask Cassandra one question') and immediately corrects a potentially misleading name by stating that this call does not return an answer but the live x402 payment requirement. That is a precise, actionable purpose. It stops short of explicitly distinguishing itself from any named sibling, so it lands at 4 rather than 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?

It lays out the required workflow clearly: this call first, then pay to the vault, then POST the transaction signature to /api/ask, with the answer binding to that payment. That is strong context for sequencing the tool correctly. It offers no explicit when-not-to-use or comparison to the sibling tools, which keeps it out of 5 territory.

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