What is x402? The HTTP Status Code That Changes Everything

We’ve learned Solana’s fundamentals. Now we get to the reason I started this journey: x402.

This protocol solves a problem I’ve had for years - how do you charge for digital content without the overhead eating your margins?

The Problem

Traditional payment options for APIs and web content:

Free tier + subscription - High friction. Users don’t want another subscription.

API keys + usage billing - Massive overhead. Billing dashboards, invoicing, payment failures.

Stripe/payment processors - 2.9% + $0.30 per transaction makes anything under $10 uneconomical.

What if charging $0.01 for an API call just… worked?

HTTP 402: Payment Required

Back in 1997, the HTTP specification included a status code that was “reserved for future use”:

402 Payment Required

The idea was simple: a server could respond with 402 to indicate “pay me first, then I’ll give you the resource.”

The problem? There was no standard way to specify how to pay. Credit cards require accounts. PayPal requires integration. The web wasn’t ready.

Until now.

Enter x402

The x402 protocol activates HTTP 402 using cryptocurrency payments:

1. Client requests resource        GET /api/expensive-thing
                                          ↓
2. Server responds with 402        402 Payment Required
   + payment requirements          {"price": "$0.01", "payTo": "..."}
                                          ↓
3. Client makes payment            (Solana transfer: 0.01 USDC)
                                          ↓
4. Client retries with proof       GET /api/expensive-thing
                                   X-PAYMENT: <proof>
                                          ↓
5. Server verifies, responds       200 OK + content

No accounts. No OAuth. No API keys. Just HTTP.

Why Solana?

x402 is chain-agnostic, but Solana is the natural fit:

Speed - 400ms transaction finality means the client isn’t waiting.

Cost - $0.00025 per transaction makes micropayments viable.

USDC - Stable pricing. $0.01 is always $0.01.

On Ethereum, the transaction fee alone would exceed most micropayment amounts.

The Protocol Flow

Let’s trace through a real x402 interaction:

Request Without Payment

GET /api/premium-content HTTP/1.1
Host: example.com

Server Response (402)

HTTP/1.1 402 Payment Required
Content-Type: application/json

{
  "x402Version": 1,
  "accepts": [{
    "scheme": "exact",
    "network": "solana-mainnet",
    "maxAmountRequired": "10000",
    "resource": "https://example.com/api/premium-content",
    "description": "Access to premium content",
    "mimeType": "application/json",
    "payTo": "DRpbCBMxVnDK7maPgWxXSa4Z4A8e3MQbSpWhdMpVRwFD",
    "maxTimeoutSeconds": 60,
    "asset": {
      "address": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v"
    },
    "extra": {}
  }]
}

The server tells the client:

Pay to this Solana address
Send this much USDC (10000 = $0.01 with 6 decimals)
Complete within 60 seconds

Client Makes Payment

The client:

Creates a Solana transaction
Transfers the requested USDC amount
Gets the transaction signature

Request With Payment Proof

GET /api/premium-content HTTP/1.1
Host: example.com
X-PAYMENT: eyJzY2hlbWUiOiJleGFjdCIsIm5ldHdvcmsiOiJzb2xhbmEtbWFpbm5ldCIsInBheWxvYWQiOnsiYXV0aG9yaXphdGlvbiI6Ijh4eFhYLi4uIn19

The X-PAYMENT header contains:

Payment scheme used
Network (solana-mainnet/devnet)
Transaction signature or authorization

Server Verifies and Responds

HTTP/1.1 200 OK
Content-Type: application/json
X-PAYMENT-RESPONSE: {"success": true, "network": "solana-mainnet"}

{
  "content": "Here's your premium content..."
}

The Facilitator

Verifying Solana transactions requires blockchain access. Rather than every server running a validator connection, x402 uses “facilitators” - trusted verification services.

Client pays ──> Solana blockchain
                      │
                      ▼
Server ──> Facilitator ──> "Payment valid!"
                │
                ▼
           Return content

Facilitators provide:

/verify - Check if a payment is valid
/settle - Confirm the payment is final
/supported - List supported networks/tokens

You can use public facilitators or run your own.

Real Adoption

x402 isn’t theoretical:

500,000+ weekly transactions on Solana
40+ partners building infrastructure
Major platforms (Cloudflare, Anthropic) supporting x402
10,000% growth in a single month

The killer use case? AI agents. LLMs can now pay for APIs autonomously - no human intervention, no API key management.

Use Cases

Pay-per-request APIs:

AI inference endpoints
Data feeds and research APIs
Compute resources

Content monetization:

Premium articles
Video content
Downloads

AI agent payments:

Autonomous API access
Agent-to-agent transactions
Micropayment marketplaces

The JavaScript Ecosystem

Several libraries exist for implementing x402:

Server-side:

x402-next - Next.js middleware
@faremeter/payment-solana - Solana-native SDK
Coinbase’s reference implementation

Client-side:

x402-solana/client - Browser/Node client
@faremeter/fetch - Fetch wrapper with auto-payment

Facilitators:

PayAI Network
Coinbase’s facilitator
Self-hosted options

What We’re Building

In the next few posts, we’ll build:

An x402 server - Express API that returns 402 and verifies payments
An x402 client - JavaScript that handles the payment flow automatically
A full Next.js app - Complete pay-per-request application

By the end, you’ll have a working template for monetizing any API or content.

The Bigger Picture

x402 isn’t just about payments. It’s about a new primitive for the web:

No accounts - Users don’t register, they pay
No trust - Payments are verified on-chain
No middlemen - Direct wallet-to-wallet transfers
No minimums - $0.001 is economically viable

This enables business models that weren’t possible before.

What You Learned

HTTP 402 “Payment Required” is finally real
x402 uses crypto payments (primarily on Solana) to gate resources
The flow: request → 402 → pay → retry with proof → 200
Facilitators handle payment verification
AI agents are a major driver of adoption

Next Up

Time to write code. We’ll build an x402 server from scratch - an Express API that requires payment and verifies transactions.

Resources: