# 402Shield

A $0.005 x402 payment firewall for autonomous agents. Screen a proposed crypto payment or EVM transaction immediately before execution.

## When to use

Call 402Shield immediately before an agent executes a crypto payment or EVM transaction when it needs a machine-readable security and policy verdict.

## Paid tool

POST /v1/decision — $0.005 USDC via x402.

Returns ALLOW, REVIEW, or BLOCK with reasons, warnings, a risk score, and evidence.
ALLOW means no configured security or policy rule produced a block or review; it is not an investment recommendation or guarantee of safety.

## Minimum request

{"requested":{"amountUsd":"0.005","recipient":"<EVM address>","network":"eip155:8453","asset":"USDC"}}

Optional fields add expected-payment policy, recipient/token evidence, exact EVM transaction intent, and transaction simulation.

## Discovery

Machine manifest: /.well-known/x402
OpenAPI: /openapi.json
LLM guide: /llms.txt
Health: /health

## Safety semantics

BLOCK: a configured security or policy rule was violated.
REVIEW: evidence is uncertain, unavailable, malformed, or warrants review.
ALLOW: no configured rule or required evidence layer produced BLOCK or REVIEW.

402Shield is advisory. It does not hold private keys, execute transactions, or provide investment advice.