agents/plugins/payment-processing/skills/stripe-integration/SKILL.md

name, description

name	description
stripe-integration	Implement Stripe payment processing for robust, PCI-compliant payment flows including checkout, subscriptions, and webhooks. Use when integrating Stripe payments, building subscription systems, or implementing secure checkout flows.

Stripe Integration

Master Stripe payment processing integration for robust, PCI-compliant payment flows including checkout, subscriptions, webhooks, and refunds.

When to Use This Skill

• Implementing payment processing in web/mobile applications
• Setting up subscription billing systems
• Handling one-time payments and recurring charges
• Processing refunds and disputes
• Managing customer payment methods
• Implementing SCA (Strong Customer Authentication) for European payments
• Building marketplace payment flows with Stripe Connect

Core Concepts

1. Payment Flows

Checkout Sessions

• Recommended for most integrations
• Supports all UI paths:
  • Stripe-hosted checkout page
  • Embedded checkout form (ui_mode='embedded')
  • Custom UI with Elements (Payment Element, Express Checkout Element) using ui_mode='custom'
• Provides built-in checkout capabilities (line items, discounts, tax, shipping, address collection, saved payment methods, and checkout lifecycle events)
• Lower integration and maintenance burden than Payment Intents

Payment Intents (Bespoke control)

• You calculate the final amount with taxes, discounts, subscriptions, and currency conversion yourself.
• More complex implementation and long-term maintenance burden
• Requires Stripe.js for PCI compliance

Setup Intents (Save Payment Methods)

• Collect payment method without charging
• Used for subscriptions and future payments
• Requires customer confirmation

2. Webhooks

Critical Events:

• payment_intent.succeeded: Payment completed
• payment_intent.payment_failed: Payment failed
• customer.subscription.updated: Subscription changed
• customer.subscription.deleted: Subscription canceled
• charge.refunded: Refund processed
• invoice.payment_succeeded: Subscription payment successful

3. Subscriptions

Components:

• Product: What you're selling
• Price: How much and how often
• Subscription: Customer's recurring payment
• Invoice: Generated for each billing cycle

4. Customer Management

• Create and manage customer records
• Store multiple payment methods
• Track customer metadata
• Manage billing details

Quick Start

import stripe

stripe.api_key = "sk_test_..."

# Create a checkout session
session = stripe.checkout.Session.create(
    line_items=[{
        'price_data': {
            'currency': 'usd',
            'product_data': {
                'name': 'Premium Subscription',
            },
            'unit_amount': 2000,  # $20.00
            'recurring': {
                'interval': 'month',
            },
        },
        'quantity': 1,
    }],
    mode='subscription',
    success_url='https://yourdomain.com/success?session_id={CHECKOUT_SESSION_ID}',
    cancel_url='https://yourdomain.com/cancel',
)

# Redirect user to session.url
print(session.url)

Payment Implementation Patterns

Pattern 1: One-Time Payment (Hosted Checkout)

def create_checkout_session(amount, currency='usd'):
    """Create a one-time payment checkout session."""
    try:
        session = stripe.checkout.Session.create(
            line_items=[{
                'price_data': {
                    'currency': currency,
                    'product_data': {
                        'name': 'Purchase',
                        'images': ['https://example.com/product.jpg'],
                    },
                    'unit_amount': amount,  # Amount in cents
                },
                'quantity': 1,
            }],
            mode='payment',
            success_url='https://yourdomain.com/success?session_id={CHECKOUT_SESSION_ID}',
            cancel_url='https://yourdomain.com/cancel',
            metadata={
                'order_id': 'order_123',
                'user_id': 'user_456'
            }
        )
        return session
    except stripe.error.StripeError as e:
        # Handle error
        print(f"Stripe error: {e.user_message}")
        raise

Pattern 2: Checkout Sessions with Payment Element

def create_checkout_session_for_elements(amount, currency='usd'):
    """Create a checkout session configured for Payment Element."""
    session = stripe.checkout.Session.create(
        mode='payment',
        ui_mode='custom',
        line_items=[{
            'price_data': {
                'currency': currency,
                'product_data': {'name': 'Purchase'},
                'unit_amount': amount,
            },
            'quantity': 1,
        }],
        return_url='https://yourdomain.com/complete?session_id={CHECKOUT_SESSION_ID}'
    )
    return session.client_secret  # Send to frontend for stripe.initCheckout()

# Frontend (JavaScript)
"""
const stripe = Stripe('pk_test_...');

// initCheckout() is synchronous; loadActions() is async
const checkout = stripe.initCheckout({clientSecret});
const loadActionsResult = await checkout.loadActions();

if (loadActionsResult.type === 'success') {
    const {actions} = loadActionsResult;
    const session = actions.getSession();

    const button = document.getElementById('pay-button');
    const checkoutContainer = document.getElementById('checkout-container');
    const emailInput = document.getElementById('email');
    const emailErrors = document.getElementById('email-errors');
    const errors = document.getElementById('confirm-errors');

    // Display grand total (amount in smallest currency unit, e.g. cents)
    checkoutContainer.append(`Total: ${session.total.total.amount}`);

    // Mount Payment Element
    const paymentElement = checkout.createPaymentElement();
    paymentElement.mount('#payment-element');

    // Store email for submission
    emailInput.addEventListener('blur', () => {
        actions.updateEmail(emailInput.value).then((result) => {
            if (result.error) emailErrors.textContent = result.error.message;
        });
    });

    // Handle form submission
    button.addEventListener('click', () => {
        actions.confirm().then((result) => {
            if (result.type === 'error') errors.textContent = result.error.message;
        });
    });
}
"""

Pattern 3: Payment Intents with Payment Element (Bespoke Control)

Use this when you need full control over the payment flow and cannot use Checkout Sessions (e.g., you have your own tax, discount, or subscription calculation engine).

def create_payment_intent(amount, currency='usd', customer_id=None):
    """Create a payment intent for bespoke checkout UI with Payment Element."""
    intent = stripe.PaymentIntent.create(
        amount=amount,
        currency=currency,
        customer=customer_id,
        automatic_payment_methods={
            'enabled': True,
        },
    )
    return intent.client_secret  # Send to frontend

// Frontend: Mount Payment Element and confirm via Payment Intents
const stripe = Stripe('pk_test_...');
const elements = stripe.elements({clientSecret});

const paymentElement = elements.create('payment');
paymentElement.mount('#payment-element');

document.getElementById('pay-button').addEventListener('click', async () => {
    const {error} = await stripe.confirmPayment({
        elements,
        confirmParams: {
            return_url: 'https://yourdomain.com/complete',
        },
    });

    if (error) {
        document.getElementById('errors').textContent = error.message;
    }
});

Pattern 4: Subscription Creation

def create_subscription(customer_id, price_id):
    """Create a subscription for a customer."""
    try:
        subscription = stripe.Subscription.create(
            customer=customer_id,
            items=[{'price': price_id}],
            payment_behavior='default_incomplete',
            payment_settings={'save_default_payment_method': 'on_subscription'},
            expand=['latest_invoice.payment_intent'],
        )

        return {
            'subscription_id': subscription.id,
            'client_secret': subscription.latest_invoice.payment_intent.client_secret
        }
    except stripe.error.StripeError as e:
        print(f"Subscription creation failed: {e}")
        raise

Pattern 5: Customer Portal

def create_customer_portal_session(customer_id):
    """Create a portal session for customers to manage subscriptions."""
    session = stripe.billing_portal.Session.create(
        customer=customer_id,
        return_url='https://yourdomain.com/account',
    )
    return session.url  # Redirect customer here

Webhook Handling

Secure Webhook Endpoint

from flask import Flask, request
import stripe

app = Flask(__name__)

endpoint_secret = 'whsec_...'

@app.route('/webhook', methods=['POST'])
def webhook():
    payload = request.data
    sig_header = request.headers.get('Stripe-Signature')

    try:
        event = stripe.Webhook.construct_event(
            payload, sig_header, endpoint_secret
        )
    except ValueError:
        # Invalid payload
        return 'Invalid payload', 400
    except stripe.error.SignatureVerificationError:
        # Invalid signature
        return 'Invalid signature', 400

    # Handle the event
    if event['type'] == 'payment_intent.succeeded':
        payment_intent = event['data']['object']
        handle_successful_payment(payment_intent)
    elif event['type'] == 'payment_intent.payment_failed':
        payment_intent = event['data']['object']
        handle_failed_payment(payment_intent)
    elif event['type'] == 'customer.subscription.deleted':
        subscription = event['data']['object']
        handle_subscription_canceled(subscription)

    return 'Success', 200

def handle_successful_payment(payment_intent):
    """Process successful payment."""
    customer_id = payment_intent.get('customer')
    amount = payment_intent['amount']
    metadata = payment_intent.get('metadata', {})

    # Update your database
    # Send confirmation email
    # Fulfill order
    print(f"Payment succeeded: {payment_intent['id']}")

def handle_failed_payment(payment_intent):
    """Handle failed payment."""
    error = payment_intent.get('last_payment_error', {})
    print(f"Payment failed: {error.get('message')}")
    # Notify customer
    # Update order status

def handle_subscription_canceled(subscription):
    """Handle subscription cancellation."""
    customer_id = subscription['customer']
    # Update user access
    # Send cancellation email
    print(f"Subscription canceled: {subscription['id']}")

Webhook Best Practices

import hashlib
import hmac

def verify_webhook_signature(payload, signature, secret):
    """Manually verify webhook signature."""
    expected_sig = hmac.new(
        secret.encode('utf-8'),
        payload,
        hashlib.sha256
    ).hexdigest()

    return hmac.compare_digest(signature, expected_sig)

def handle_webhook_idempotently(event_id, handler):
    """Ensure webhook is processed exactly once."""
    # Check if event already processed
    if is_event_processed(event_id):
        return

    # Process event
    try:
        handler()
        mark_event_processed(event_id)
    except Exception as e:
        log_error(e)
        # Stripe will retry failed webhooks
        raise

Customer Management

def create_customer(email, name, payment_method_id=None):
    """Create a Stripe customer."""
    customer = stripe.Customer.create(
        email=email,
        name=name,
        payment_method=payment_method_id,
        invoice_settings={
            'default_payment_method': payment_method_id
        } if payment_method_id else None,
        metadata={
            'user_id': '12345'
        }
    )
    return customer

def attach_payment_method(customer_id, payment_method_id):
    """Attach a payment method to a customer."""
    stripe.PaymentMethod.attach(
        payment_method_id,
        customer=customer_id
    )

    # Set as default
    stripe.Customer.modify(
        customer_id,
        invoice_settings={
            'default_payment_method': payment_method_id
        }
    )

def list_customer_payment_methods(customer_id):
    """List all payment methods for a customer."""
    payment_methods = stripe.PaymentMethod.list(
        customer=customer_id,
        type='card'
    )
    return payment_methods.data

Refund Handling

def create_refund(payment_intent_id, amount=None, reason=None):
    """Create a refund."""
    refund_params = {
        'payment_intent': payment_intent_id
    }

    if amount:
        refund_params['amount'] = amount  # Partial refund

    if reason:
        refund_params['reason'] = reason  # 'duplicate', 'fraudulent', 'requested_by_customer'

    refund = stripe.Refund.create(**refund_params)
    return refund

def handle_dispute(charge_id, evidence):
    """Update dispute with evidence."""
    stripe.Dispute.modify(
        charge_id,
        evidence={
            'customer_name': evidence.get('customer_name'),
            'customer_email_address': evidence.get('customer_email'),
            'shipping_documentation': evidence.get('shipping_proof'),
            'customer_communication': evidence.get('communication'),
        }
    )

Testing

# Use test mode keys
stripe.api_key = "sk_test_..."

# Test card numbers
TEST_CARDS = {
    'success': '4242424242424242',
    'declined': '4000000000000002',
    '3d_secure': '4000002500003155',
    'insufficient_funds': '4000000000009995'
}

def test_payment_flow():
    """Test complete payment flow."""
    # Create test customer
    customer = stripe.Customer.create(
        email="test@example.com"
    )

    # Create payment intent
    intent = stripe.PaymentIntent.create(
        amount=1000,
        currency='usd',
        customer=customer.id,
        automatic_payment_methods={'enabled': True},
    )

    # Confirm with test card
    confirmed = stripe.PaymentIntent.confirm(
        intent.id,
        payment_method='pm_card_visa'  # Test payment method
    )

    assert confirmed.status == 'succeeded'

Resources

• references/checkout-flows.md: Detailed checkout implementation
• references/webhook-handling.md: Webhook security and processing
• references/subscription-management.md: Subscription lifecycle
• references/customer-management.md: Customer and payment method handling
• references/invoice-generation.md: Invoicing and billing
• assets/stripe-client.py: Production-ready Stripe client wrapper
• assets/webhook-handler.py: Complete webhook processor
• assets/checkout-config.json: Checkout configuration templates

Best Practices

1. Always Use Webhooks: Don't rely solely on client-side confirmation
2. Idempotency: Handle webhook events idempotently
3. Error Handling: Gracefully handle all Stripe errors
4. Test Mode: Thoroughly test with test keys before production
5. Metadata: Use metadata to link Stripe objects to your database
6. Monitoring: Track payment success rates and errors
7. PCI Compliance: Never handle raw card data on your server
8. SCA Ready: Implement 3D Secure for European payments

Common Pitfalls

• Not Verifying Webhooks: Always verify webhook signatures
• Missing Webhook Events: Handle all relevant webhook events
• Hardcoded Amounts: Use cents/smallest currency unit
• No Retry Logic: Implement retries for API calls
• Ignoring Test Mode: Test all edge cases with test cards