ExchangeRebel — pay-per-call APIs for AI agents (x402 on Solana)

rail_probe_precheck

FREE headline pre-check (100/day per wallet; pass caller). Returns assessability only - whether the URL is in-policy; the endpoint is not probed and no grade is returned. The full signed report is the paid rail_probe_probe call.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "caller": "<caller>",
      "url": "<url>"
    },
    "name": "rail_probe_precheck"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	The one endpoint URL the 7-probe set runs against after payment. Probe responses are processed in memory only and never stored.
`caller`	Yes	Solana base58 wallet of the operator; keys the free allowance (100/day per wallet).

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 3, 2026

TDQS

A4.2/5.0

Behavior4/5

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

With no annotations, the description carries the full load and does well: it discloses the rate limit (100/day per wallet), that the caller wallet is required and keys the allowance, and — critically — that the endpoint is not actually probed and no grade is returned, preventing a false expectation of real results. What's missing is the response shape for 'assessability' (boolean vs enum) and any error/quota-exhausted behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, zero filler, with the most decision-relevant facts front-loaded (free, rate limit, what is returned) followed by the negative scope and the paid alternative. Every clause earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter tool with no annotations and no output schema, the description covers the essentials: cost, quota, what the call does and does not do, and the upgrade path. The only real gap is the concrete shape of the returned 'assessability' value, which nothing else in the definition supplies.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so both parameters are already documented, including the wallet-keyed allowance and the one-URL-per-call constraint. The description restates the 100/day-per-wallet limit and 'pass caller' but adds no syntax, format, or edge-case meaning beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description gives a specific verb and resource ('FREE headline pre-check' of a URL's in-policy status) and explicitly bounds the scope: 'Returns assessability only ... the endpoint is not probed and no grade is returned.' It also names the sibling rail_probe_probe as the thing this is not, so an agent can distinguish the two without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is clearly framed: this is the free pre-check, and 'the full signed report is the paid rail_probe_probe call' points to the alternative with the condition (paid/full report) that selects it. It stops short of an explicit 'use this first, then upgrade' instruction or stating when the pre-check is unnecessary, 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.

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