x402 agent toolkit: service finder, payment safety, Solana & web tools

by dev.workers.moneytools.x402-pay-precheck

Calldata decoder

calldata_decode

Read-onlyIdempotent

Decode raw EVM calldata before signing: function name and typed arguments via the open Sourcify signature DB (or your ABI / signature), plus a plain-language meaning for risky selectors (approve, setApprovalForAll, permit...). Free: 10 calls/day; then $0.001/call via x402 (MCP params._meta["x402/payment"] or HTTP) or X-API-Key credits. [served by tools.moneytools.dev]

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": {
      "data": "<data>"
    },
    "name": "calldata_decode"
  }
}

Input Schema

Name	Required	Description
`abi`	No	JSON ABI array
`data`	Yes	0x calldata
`signature`	No	e.g. transfer(address,uint256)

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 4, 2026

TDQS

A4.3/5.0

Behavior5/5

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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes well beyond them: it discloses the external Sourcify lookup (openWorld), a 10 calls/day free tier with $0.001/call thereafter, and the two payment paths (x402 via _meta or HTTP, X-API-Key credits). That rate-limit and auth detail is exactly the context an agent needs before calling and is not available in structured fields.

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

Conciseness4/5

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

The purpose and output set are front-loaded in the first sentence, with pricing/auth following. The pricing clause is dense but earns its place because payment failure is a real call-time risk; only minor trimming would be possible.

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?

With an output schema present, return values need no explanation, and all three params are schema-documented. The one omission is fallback behavior when a selector is absent from Sourcify and no ABI/signature is supplied — an agent cannot tell whether that errors or returns partial data.

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 'data', 'abi', and 'signature' are already documented, and the example calldata in the schema is more instructive than anything in the description. The description adds only a weak hint of precedence ('or your ABI / signature') without explaining which source wins when multiple are supplied — baseline 3.

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?

States a specific verb and resource ('Decode raw EVM calldata') and enumerates the exact outputs: function name, typed arguments, and plain-language meaning for risky selectors. The decode-vs-encode distinction against sibling abi_encode is obvious from the verb alone, so an agent can route without opening the 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?

'before signing' gives a concrete usage context, and the parenthetical '(or your ABI / signature)' hints at the input path. It stops short of naming an alternative tool or stating exclusions (e.g., when to use abi_encode or contract_read instead), so it is clear context without routing rules.

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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