I’ve spent the last 2 weeks integrating x402 into various projects, testing every SDK available. Here’s my honest review of the developer experience across languages.
The “1 Line of Code” Promise:
Marketing claim:
“Add payments to any API with 1 line of code”
Reality: It’s actually pretty close to true! Here’s what “1 line” looks like:
JavaScript (Express)
import { paymentMiddleware } from "x402-express";
app.use(paymentMiddleware("0xYourAddress", {
"GET /data": { price: "$0.01", network: "base" }
}));
Python (FastAPI)
from x402.fastapi.middleware import require_payment
app.middleware("http")(
require_payment(
path="/data",
price="$0.01",
pay_to_address="0xYourAddress",
network="base"
)
)
Rust (Axum)
use x402_rs::middleware::X402Layer;
let app = Router::new()
.route("/data", get(handler))
.layer(X402Layer::new()
.price(Decimal::new(1, 2)) // $0.01
.network(Network::Base)
.recipient("0xYourAddress")
);
Java (Spring Boot / Mogami)
@RestController
public class DataController {
@GetMapping("/data")
@RequirePayment(price = "0.01", network = "base")
public String getData() {
return "Protected data";
}
}
Verdict: The middleware approach IS simple. Setup takes 5-10 minutes.
SDK Comparison (Real-World Testing):
| SDK | Language | Maturity | Docs | Community | Rating |
|---|---|---|---|---|---|
| coinbase/x402 | TypeScript |  |
Excellent | Large | 9/10 |
| x402-rs | Rust | |
Good | Medium | 8/10 |
| Mogami | Java | |
Good | Small | 8/10 |
| x402 (PyPI) | Python | |
Basic | Small | 7/10 |
| a2a-x402 | Multi | |
Medium | Small | 7/10 |
Deep Dive: Coinbase x402 SDK (JavaScript/TypeScript)
This is the reference implementation. Most mature.
Installation:
npm install x402-express x402-axios
# or
pnpm add x402-express x402-axios
Server Setup (5 minutes):
import express from "express";
import { paymentMiddleware, Network } from "x402-express";
const app = express();
// 1. Add payment middleware
app.use(paymentMiddleware(
process.env.RECIPIENT_ADDRESS,
{
"GET /weather": {
price: "$0.001",
network: "base"
},
"POST /analyze": {
price: "$0.10",
network: "base"
}
},
{
facilitatorUrl: "https://api.x402.org/facilitator"
}
));
// 2. Define your endpoints (no payment code needed!)
app.get("/weather", (req, res) => {
res.json({ temp: 72, conditions: "sunny" });
});
app.post("/analyze", (req, res) => {
// Expensive operation - worth $0.10
const analysis = performAnalysis(req.body);
res.json(analysis);
});
app.listen(3000);
Client Usage:
import { x402Axios } from "x402-axios";
const client = x402Axios.create({
wallet: {
address: process.env.WALLET_ADDRESS,
privateKey: process.env.PRIVATE_KEY
},
network: "base"
});
// Make payment automatically!
const response = await client.get("https://api.example.com/weather");
// SDK handles: 402 response → create payment → retry with X-PAYMENT header
What happens under the hood:
- Client makes request
- Server returns 402 with payment requirements
- SDK creates payment transaction on Base
- SDK waits for confirmation (~2 seconds)
- SDK retries request with payment proof
- Server returns data
Deep Dive: x402-rs (Rust)
Why Rust matters:
- Performance: 10x faster than JavaScript for payment verification
- Safety: Memory safety prevents vulnerabilities
- Concurrency: Handle 1000s of concurrent payments
Installation:
cargo add x402-rs tokio axum
Server Example:
use axum::{Router, routing::get, Json};
use x402_rs::{middleware::X402Layer, types::Decimal, Network};
#[tokio::main]
async fn main() {
let app = Router::new()
.route("/data", get(get_data))
.layer(
X402Layer::new()
.recipient("0xYourAddress".parse().unwrap())
.price(Decimal::new(1, 2)) // $0.01
.network(Network::Base)
.facilitator_url("https://api.x402.org/facilitator")
);
let listener = tokio::net::TcpListener::bind("0.0.0.0:3000")
.await
.unwrap();
axum::serve(listener, app).await.unwrap();
}
async fn get_data() -> Json<serde_json::Value> {
Json(serde_json::json!({
"data": "Protected content"
}))
}
Running a Facilitator:
# x402-rs includes a reference facilitator!
cargo install x402-rs-facilitator
x402-facilitator --network base --rpc-url $BASE_RPC_URL --port 8080
This is HUGE for BlockEden - you could run your own facilitator using x402-rs.
Deep Dive: Mogami (Java)
Best for:
- Enterprise Java shops
- Spring Boot applications
- Teams already using Java ecosystem
Installation (Maven):
<dependency>
<groupId>tech.mogami</groupId>
<artifactId>mogami-x402-spring-boot-starter</artifactId>
<version>1.0.0</version>
</dependency>
Configuration:
# application.yml
mogami:
x402:
recipient-address: 0xYourAddress
network: base
facilitator-url: https://api.x402.org/facilitator
Usage:
@RestController
@RequestMapping("/api")
public class DataController {
@GetMapping("/public")
public String publicEndpoint() {
return "Free data";
}
@GetMapping("/premium")
@RequirePayment(price = "0.01", currency = "USD")
public PremiumData premiumEndpoint() {
return new PremiumData(...);
}
@PostMapping("/analysis")
@RequirePayment(price = "1.00", currency = "USD")
public AnalysisResult analyze(@RequestBody AnalysisRequest req) {
// Expensive computation worth $1
return performAnalysis(req);
}
}
Java Client:
import tech.mogami.x402.client.X402Client;
X402Client client = X402Client.builder()
.wallet(walletAddress, privateKey)
.network(Network.BASE)
.build();
// Make payment automatically
String response = client.get("https://api.example.com/premium");
Common Pitfalls (Save yourself hours):
Pitfall 1: Wrong Network
// ❌ Server on base, client on ethereum
// Server
{ network: "base" }
// Client
{ network: "ethereum" }
// Result: Payment on wrong chain, verification fails
Fix: Use environment variables for network config.
Pitfall 2: Facilitator Down
// ❌ Hardcoded facilitator URL
facilitatorUrl: "https://random-facilitator.com"
// Goes down → all payments fail
Fix: Use multiple facilitators with fallback:
{
facilitators: [
"https://api.x402.org/facilitator", // Primary
"https://backup.x402.org/facilitator" // Fallback
]
}
Pitfall 3: No Error Handling
// ❌ Assume payment always succeeds
const data = await client.get(url);
Fix:
try {
const data = await client.get(url);
} catch (error) {
if (error.code === 'INSUFFICIENT_FUNDS') {
alert("Please add USDC to your wallet");
} else if (error.code === 'PAYMENT_TIMEOUT') {
alert("Payment verification timed out. Try again.");
} else {
// Log to Sentry, etc.
}
}
For BlockEden Integration:
Option 1: Wrap Existing SDKs
import { BlockEdenX402 } from '@blockeden/x402-sdk';
import { x402Axios } from 'x402-axios';
// Thin wrapper around x402-axios
export const BlockEdenX402 = {
create: (config) => {
return x402Axios.create({
...config,
baseURL: "https://blockeden.xyz/x402",
facilitatorUrl: "https://blockeden.xyz/facilitator"
});
}
};
Option 2: Build Native SDKs
More work, but better developer experience:
import { BlockEden } from '@blockeden/sdk';
const client = new BlockEden({
apiKey: "traditional-key", // OR
wallet: "0x...", // x402 mode
payment: {
network: "base",
maxPricePerCall: 0.01
}
});
// Same API works with both auth methods!
const balance = await client.eth.getBalance("0x...");
My Recommendations:
- Start with JavaScript SDK - most mature, best docs
- Use Rust for facilitators - performance + safety
- Java for enterprises - Mogami is production-ready
- Python is…okay - needs more work, but usable
The x402 SDK ecosystem is READY for production. The developer experience is actually quite good - better than I expected.
BlockEden should offer SDKs for ALL languages, wrapping the best existing implementations.