Axiom Relay MCP Server

Axiom Relay

An x402 smart router for autonomous agents. Describe the capability you need instead of a URL; Axiom finds a provider that actually works, pays the seller directly, and returns the result.

Live on Base mainnet: https://axiom-relay.reference-seller.workers.dev

Why this exists

Most x402 tooling assumes the agent already knows the provider's URL. In practice it doesn't — and roughly 13% of advertised x402 providers do not answer a valid challenge when actually called (measured across the live Coinbase Bazaar catalogue). Axiom absorbs that problem.

intent -> discover candidates -> validate -> rank -> pay -> return result

Pricing

The fee is a percentage below ~$16.67 and flat above it, so a $25 purchase and a $250 purchase both cost $0.50.

Non-custodial by construction

The buyer signs two independent authorisations: one payable directly to the seller, one payable to Axiom. Axiom relays the seller's authorisation without modification and cannot alter its amount or destination.

• Seller funds never enter an Axiom-controlled address.
• Axiom holds no signing key at all — it cannot move your money.
• Exactly one routing fee per completed purchase, charged only on success.
• Fallback advances only on positive evidence the previous seller was not paid; an ambiguous settlement halts the chain rather than risk a double payment.

Quickstart

npm install axiom-relay

import { Axiom } from 'axiom-relay';
import { x402Client } from '@x402/core/client';
import { registerExactEvmScheme } from '@x402/evm/exact/client';
import { privateKeyToAccount } from 'viem/accounts';

const signer = new x402Client();
registerExactEvmScheme(signer, { signer: privateKeyToAccount(process.env.KEY) });

const axiom = new Axiom({ baseUrl: 'https://axiom-relay.reference-seller.workers.dev' });

const { route, result } = await axiom.buy(signer, 'crypto price', {
  network: 'eip155:8453',
});

console.log(route.selectionReason);
console.log(result.downstream.body);

Or with plain HTTP:

curl -sX POST https://axiom-relay.reference-seller.workers.dev/v1/route \
  -H 'content-type: application/json' \
  -d '{"capability":"crypto price","requirements":{"network":"eip155:8453"}}'

How routing decides

Deterministic, no learning, no hidden preference:

score = (50*reliability + 30*price + 10*latency + 10*freshness) / 100

Reliability leads on purpose — a cheap provider that fails costs the agent a round trip and earns Axiom nothing. When the winner is not the cheapest, the response says so and names the price premium and the reliability figures that outweighed it. Ties break on provider id, so ordering is stable.

Machine integration

MCP

{
  "mcpServers": {
    "axiom": { "type": "http", "url": "https://axiom-relay.reference-seller.workers.dev/mcp" }
  }
}

Tools: find_paid_resource, quote_paid_resource, purchase_paid_resource, check_provider. The MCP layer is a thin adapter over the HTTP API — it contains no payment logic, so the safety properties are identical.

Examples

See examples/: raw TypeScript, MCP, OpenAI tools, Claude Agent Skills, LangChain, Cloudflare Agents, and a generic x402 client.

Two behaviours worth knowing

Waived fee. When feePolicy is fee_waived_micropayment, axiomFee is 0 and payTo is null. Do not sign a fee leg — there is nothing to authorise.

Free-route quota. free_route_quota_exhausted (HTTP 429) means the purchase is valid and the provider healthy, but Axiom's free-routing allocation is spent. The response carries resetsAt. Purchases whose fee is collectible are never quota-limited.

Security model

• x402 v2, exact scheme, USDC on Base.
• Destination URLs are validated against SSRF: loopback, RFC1918, link-local, cloud metadata, IPv4-mapped and NAT64 embeddings, embedded credentials and non-web ports are refused, and every redirect hop is revalidated independently.
• Replay protection claims each EIP-3009 authorisation nonce atomically.
• A discovered provider is an untrusted claim: schema-checked, SSRF-validated and probed for a live challenge before it can be selected.

Status

Live on Base mainnet with real settlements. Base Sepolia also supported for testing. Current state is always readable at /health.

Licence

MIT