@true402.dev/mcp-server

tx_preflight

Instructions

Check a Base transaction BEFORE signing it. POST an UNSIGNED transaction { from, to, data?, value? } and get three independent lenses: simulation against current state (does it revert?), decoded intent (is this an unlimited approval that outlives the trade?), and the counterparty liquidity-removal history from our own archive. Takes NO private key and NO signature, so the service cannot broadcast or front-run the transaction it inspects — a deliberate security property. It never returns "safe": a clean result means these checks found nothing, and the limits array says so in every response. Unpaid: free while the caller's IP has free-trial calls left that day (a small daily allowance shared across the trial stalls, no wallet); otherwise returns 402. (PAID x402 service — USDC on Base; the MCP server needs a funded wallet to settle.) Price: $0.008 USD (fixed).

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": {
      "from": "<from>",
      "to": "<to>"
    },
    "name": "tx_preflight"
  }
}

Input Schema

Name	Required	Description
`to`	Yes	Destination contract or address
`data`	No	Calldata hex (0x…); omit for a plain native transfer
`from`	Yes	Sender address. Asserted, never proven — no signature is taken.
`value`	No	Native value in wei as a decimal string; default 0

Schema Changelog

Changes observed during successful MCP inspections.

Addedv1.3.0Oct 22, 2026

TDQS

A4.4/5.0

Behavior5/5

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

No annotations exist, and the description carries the full burden well: it discloses the security property (no key, no signature, cannot broadcast or front-run), the epistemics of the result (never returns 'safe'; a clean result means nothing was found and `limits` says so every time), and the payment behavior (free-trial IP allowance, otherwise 402, $0.008 fixed, MCP server needs a funded wallet). These are exactly the traits an agent cannot infer from the schema.

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?

Front-loaded with the action and then the three lenses; every clause is substantive. The payment paragraph runs two sentences where one would do, a minor redundancy but not filler.

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

Completeness5/5

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

With no annotations and no output schema, the description still tells the agent what comes back (simulation, decoded intent, counterparty liquidity-removal history, plus a `limits` array), what a clean result means, and the payment failure mode (402). Nothing needed to call it correctly is missing.

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% and the field descriptions are already substantive (e.g., 'Asserted, never proven — no signature is taken'). The description only restates the object shape `{ from, to, data?, value? }`, adding no format or edge-case guidance 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?

States a specific verb and resource ('Check a Base transaction BEFORE signing it') plus the exact input shape it accepts. It is clearly distinguishable from sibling safety tools (token_safety, address_safety, honeypot), which inspect tokens/addresses rather than a specific unsigned transaction.

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?

Gives an explicit timing condition ('BEFORE signing it') and the invocation contract (POST an unsigned transaction to get three lenses). It does not name a sibling alternative or state when-not to use it, but the use case is unambiguous.

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