zkapi_pay_privately_info

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

With no annotations supplied, the description carries the burden and does reasonably well: it discloses the return payload ('endpoint URLs, prices, and a minimal example') and explains the mechanics of both rails (deposit + Groth16 proof in X-Zkapi-Proof, or one x402 payment for a session key used via X-Zkapi-Session). It does not explicitly state that this call itself is free/read-only or whether any auth is required, which is the main residual gap.

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 short lines with the core framing front-loaded, then two enumerated rails, then the return content. Every clause carries load — header names, proof type, and payment model are all actionable detail rather than filler.

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 zero-parameter informational tool with no output schema and no annotations, the description supplies what an agent needs: which rails exist, how each authenticates, and what the response will contain. It stops short of detailing pricing structure or the exact example format, but that is minor at this complexity.

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 tool takes zero parameters, so the schema baseline of 4 applies; there is no parameter meaning for the description to add or omit.

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 opens with a specific verb and subject ('Explain the two private payment rails for agents without an x402 wallet') and enumerates the two rails by name (ZK rail, session rail). It is clearly distinguishable from sibling tools like zkapi_health or get_x402_scaffold, though it does not explicitly name those siblings as alternatives.

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 audience condition 'for agents without an x402 wallet' gives a concrete when-to-use signal, and the two enumerated rails describe the follow-up path each option leads to. There are no explicit when-not-to-use exclusions or named alternative tools, which keeps it below a 5.

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