SDKs & Libraries

Official API Express SDKs handle authentication, request formatting, retry logic, and error handling out of the box. Install in seconds, integrate in minutes. All SDKs are open-source and available on GitHub.

Overview

SDKs are optional — you can always call the API directly with HTTP requests. But for production applications, SDKs provide real value:

• Automatic authentication — Set your key once, every request includes it
• Typed methods per API — client.recharge.send(...), client.kyc.verifyPan(...)
• Built-in retry logic — Handles 429s and 5xx errors with exponential backoff
• Consistent error handling — Throws typed exceptions instead of generic HTTP errors
• Automatic environment switching — Sandbox vs production with one flag
• Webhook signature verification — One-line helpers for verifying event signatures

Node.js SDK

Installation

npm install @apiexpress/sdk

Or with yarn:

yarn add @apiexpress/sdk

Initialize the client

const { ApiExpress } = require('@apiexpress/sdk');

const client = new ApiExpress({
  apiKey: process.env.API_KEY,
  environment: 'production' // or 'sandbox'
});

With TypeScript (recommended):

import { ApiExpress } from '@apiexpress/sdk';

const client = new ApiExpress({
  apiKey: process.env.API_KEY!,
  environment: process.env.NODE_ENV === 'production' ? 'production' : 'sandbox'
});

Basic usage

// Weather API
const weather = await client.weather.get({
  city: 'Mumbai'
});
console.log(weather.temp); // 31.5

// Mobile Recharge API
const recharge = await client.recharge.send({
  mobile: '9876543210',
  operator: 'auto',
  amount: 199
});
console.log(recharge.transaction_id);

// KYC PAN verification
const kyc = await client.kyc.verifyPan({
  pan: 'ABCDE1234F',
  name: 'Arjun Sharma'
});
console.log(kyc.verified); // true

Error handling

const { ApiExpressError } = require('@apiexpress/sdk');

try {
  await client.recharge.send({ /* ... */ });
} catch (error) {
  if (error instanceof ApiExpressError) {
    console.error(error.code);        // 'RATE_LIMIT_EXCEEDED'
    console.error(error.message);     // 'Too many requests.'
    console.error(error.statusCode);  // 429
    console.error(error.requestId);   // 'req_1a2b3c4d5e6f'
  }
}

Automatic retry

The SDK retries 429s and 5xx errors automatically (3 attempts by default):

const client = new ApiExpress({
  apiKey: process.env.API_KEY,
  maxRetries: 5 // optional, default: 3
});

Webhook verification

const { verifyWebhook } = require('@apiexpress/sdk');

app.post('/webhooks/apiexpress',
  express.raw({ type: 'application/json' }),
  (req, res) => {
    const isValid = verifyWebhook({
      payload: req.body.toString(),
      signature: req.headers['x-apix-signature'],
      secret: process.env.WEBHOOK_SECRET
    });

    if (!isValid) return res.status(401).send('Invalid signature');

    const event = JSON.parse(req.body.toString());
    // Handle event...

    res.status(200).send('OK');
  }
);

Python SDK

Installation

pip install apiexpress

Initialize the client

from apiexpress import ApiExpress

client = ApiExpress(
    api_key=os.environ["API_KEY"],
    environment="production"  # or "sandbox"
)

Basic usage

# Weather API
weather = client.weather.get(city="Mumbai")
print(weather.temp)  # 31.5

# Mobile Recharge API
recharge = client.recharge.send(
    mobile="9876543210",
    operator="auto",
    amount=199
)
print(recharge.transaction_id)

# KYC PAN verification
kyc = client.kyc.verify_pan(
    pan="ABCDE1234F",
    name="Arjun Sharma"
)
print(kyc.verified)  # True

Error handling

from apiexpress import ApiExpressError

try:
    client.recharge.send(mobile="...", amount=199)
except ApiExpressError as e:
    print(e.code)         # 'RATE_LIMIT_EXCEEDED'
    print(e.message)      # 'Too many requests.'
    print(e.status_code)  # 429
    print(e.request_id)   # 'req_1a2b3c4d5e6f'

Automatic retry

client = ApiExpress(
    api_key=os.environ["API_KEY"],
    max_retries=5  # default: 3
)

Webhook verification (Flask example)

from apiexpress import verify_webhook
from flask import Flask, request

app = Flask(__name__)

@app.route('/webhooks/apiexpress', methods=['POST'])
def handle_webhook():
    raw_body = request.get_data(as_text=True)
    signature = request.headers.get('X-APIX-Signature')

    if not verify_webhook(
        payload=raw_body,
        signature=signature,
        secret=os.environ["WEBHOOK_SECRET"]
    ):
        return "Invalid signature", 401

    event = request.get_json()
    # Handle event...
    return "OK", 200

PHP SDK

Installation

composer require apiexpress/sdk

Initialize the client

<?php
use ApiExpress\ApiExpress;

$client = new ApiExpress([
    'api_key' => getenv('API_KEY'),
    'environment' => 'production' // or 'sandbox'
]);

Basic usage

<?php
// Weather API
$weather = $client->weather->get(['city' => 'Mumbai']);
echo $weather->temp; // 31.5

// Mobile Recharge API
$recharge = $client->recharge->send([
    'mobile' => '9876543210',
    'operator' => 'auto',
    'amount' => 199
]);
echo $recharge->transaction_id;

// KYC PAN verification
$kyc = $client->kyc->verifyPan([
    'pan' => 'ABCDE1234F',
    'name' => 'Arjun Sharma'
]);
var_dump($kyc->verified); // true

Error handling

<?php
use ApiExpress\ApiExpressException;

try {
    $client->recharge->send(['mobile' => '...', 'amount' => 199]);
} catch (ApiExpressException $e) {
    echo $e->getCode();        // 'RATE_LIMIT_EXCEEDED'
    echo $e->getMessage();     // 'Too many requests.'
    echo $e->getHttpStatus();  // 429
    echo $e->getRequestId();   // 'req_1a2b3c4d5e6f'
}

Webhook verification

<?php
use ApiExpress\Webhook;

$rawBody = file_get_contents('php://input');
$signature = $_SERVER['HTTP_X_APIX_SIGNATURE'] ?? '';

$isValid = Webhook::verify([
    'payload' => $rawBody,
    'signature' => $signature,
    'secret' => getenv('WEBHOOK_SECRET')
]);

if (!$isValid) {
    http_response_code(401);
    exit('Invalid signature');
}

$event = json_decode($rawBody, true);
// Handle event...

http_response_code(200);
echo 'OK';

Community SDKs

These SDKs are maintained by the community. They're not officially supported by API Express, but they're actively maintained and widely used.

Go

go get github.com/apiexpress/go

import "github.com/apiexpress/go"

client := apiexpress.NewClient(os.Getenv("API_KEY"))

weather, err := client.Weather.Get("Mumbai")
if err != nil {
    log.Fatal(err)
}
fmt.Println(weather.Temp)

Ruby

gem install apiexpress

require 'apiexpress'

client = ApiExpress::Client.new(api_key: ENV['API_KEY'])

weather = client.weather.get(city: 'Mumbai')
puts weather.temp

Java

<dependency>
  <groupId>in.apiexpress</groupId>
  <artifactId>sdk</artifactId>
  <version>0.7.2</version>
</dependency>

ApiExpressClient client = new ApiExpressClient(System.getenv("API_KEY"));

WeatherResponse weather = client.weather().get("Mumbai");
System.out.println(weather.getTemp());

Best Practices

Always use environment variables for API keys

Never hardcode API keys in your source code. Use environment variables or a secrets manager. Every SDK reads from whatever you pass, so pass from env:

// ✅ Correct
const client = new ApiExpress({
  apiKey: process.env.API_KEY,
  environment: process.env.NODE_ENV === 'production' ? 'production' : 'sandbox'
});

// ❌ Never do this
const client = new ApiExpress({
  apiKey: 'sk_live_1a2b3c4d5e6f...'
});

Use the SDK's automatic retry

All official SDKs implement exponential backoff with jitter for 429 and 5xx errors. Don't disable this unless you have a specific reason.

Handle typed errors, not raw HTTP errors

SDKs throw typed exceptions. Catch them explicitly instead of parsing HTTP responses yourself:

// ✅ Correct
try {
  await client.recharge.send({ /* ... */ });
} catch (error) {
  if (error.code === 'RATE_LIMIT_EXCEEDED') {
    // Wait and retry
  }
}

// ❌ Not recommended
const res = await fetch(url);
if (res.status === 429) { /* ... */ }

Use webhook verification helpers

Every SDK includes a one-line signature verification helper. Never process a webhook event without verifying the signature first.

Upgrade SDKs regularly

SDK updates include performance improvements, new API endpoints, and security fixes. Keep them up to date — most dependency managers make this trivial.

# Node.js
npm update @apiexpress/sdk

# Python
pip install --upgrade apiexpress

# PHP
composer update apiexpress/sdk

Related Documentation

• Authentication — API key setup and best practices
• Error Codes — Handle every error gracefully
• Webhooks — Verify webhook signatures
• Sandbox Testing — Test with SDKs in the sandbox