carbon-layer 0.6.0

Chaos engineering for payment flows

Carbon Layer

Chaos engineering for payment flows.

Every company processing payments tests the happy path — payment succeeds, order fulfilled — and ships. What breaks in production is everything else: dispute spikes your system doesn't respond to, refund storms that break reconciliation, gateway errors that leave orders stuck, webhook sequences your handlers were never tested against.

Carbon Layer lets you simulate these failure modes against your own integration before your customers encounter them. Run a scenario, point it at your webhook endpoint, and see exactly what your system handles and what it doesn't.

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Installation

Option A: Quick start (no database needed)

pip install carbon-layer

Works out of the box. Carbon Layer uses SQLite by default — data is stored in ~/.carbon/carbon.db. Nothing else to install or configure.

Option B: With PostgreSQL (if you already have it)

pip install carbon-layer[postgres]

Then set your connection string via a .env file or environment variable:

# .env file in your project directory
DATABASE_URL=postgresql://postgres:yourpassword@localhost:5432/carbon

Or with Docker:

docker run -d --name carbon-pg \
  -e POSTGRES_PASSWORD=carbon \
  -e POSTGRES_DB=carbon \
  -p 5432:5432 postgres:15

# then set:
DATABASE_URL=postgresql://postgres:carbon@localhost:5432/carbon

Both options support all features. You can start with SQLite and switch to PostgreSQL anytime by installing the extra and setting DATABASE_URL.

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Quickstart

# List available scenarios
carbon scenarios-list

# Run your first scenario
carbon run dispute-spike --provider mock

# View the report (use the run_id from the output above)
carbon report --run-id <run_id>

No payment gateway account needed. The mock adapter simulates the full payment lifecycle locally.

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Webhook Simulation

The real value of Carbon Layer is testing your webhook handlers. Point it at your endpoint and it fires provider-specific webhook events — payment.captured, payment_intent.succeeded, PAYMENT_SUCCESS_WEBHOOK, ORDER_SUCCEEDED, and more — after the scenario runs. Payloads are signed exactly like real webhooks from each provider (Razorpay, Stripe, Cashfree, Juspay).

carbon run dispute-spike --provider mock --webhook-url http://localhost:8000/webhooks

The report shows how your endpoint responded for each event type — 2xx, 4xx, 5xx, or timeout. No payment gateway account required.

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Scenarios

Scenario	What it tests
dispute-spike	15% dispute rate — does your system respond and submit evidence?
payment-decline-spike	30% payment failure rate — does your retry and order state logic hold?
refund-storm	Mass refunds on captured payments — does reconciliation break?
flash-sale	High order and payment volume — does throughput hold?
gateway-error-burst	Intermittent gateway errors — are orders left in inconsistent state?
min-amount	Minimum paise transactions — are edge-case amounts handled correctly?
max-amount	Large-value transactions — are limits and approvals handled correctly?
upi-timeout	UPI payments stuck without terminal status — does your reconciliation catch it?
vpa-not-found	Invalid UPI VPA failures — does your handler distinguish VPA errors from general failures?
mandate-rejection	UPI autopay mandate rejections — does your handler notify the customer?
settlement-delay	Refunds on captured-but-unsettled payments — does reconciliation handle it?

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Parameter Overrides

Override scenario parameters at runtime without editing YAML:

carbon run dispute-spike --provider mock --set baseline_orders=500 --set dispute_rate=0.3

Use --set multiple times for multiple parameters. Unknown keys are ignored with a warning.

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HTML Reports

Export a shareable HTML report after any run:

carbon report --run-id <run_id> --format html

Writes carbon_report_<run_id>.html to the current directory. Self-contained, no external dependencies — safe to share with your team or attach to an incident report.

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Webhook Resilience Testing

Test how your webhook handler behaves under real-world failure conditions.

Idempotency (duplicate webhooks)

Fire each webhook multiple times to test whether your handler processes duplicates:

carbon run dispute-spike --provider mock --webhook-url http://localhost:8000/webhooks --webhook-repeat 5

Out-of-order delivery

Gateways don't guarantee webhook order. Test with randomized or reversed delivery:

carbon run dispute-spike --provider mock --webhook-url http://localhost:8000/webhooks --webhook-order random

Options: sequence (default), reverse, random.

Signature verification

Test whether your handler actually validates webhook signatures:

# Missing signatures — should your handler reject these?
carbon run dispute-spike --provider mock --webhook-url http://localhost:8000/webhooks --webhook-signature missing

# Corrupted signatures
carbon run dispute-spike --provider mock --webhook-url http://localhost:8000/webhooks --webhook-signature corrupted

# Signed with wrong secret
carbon run dispute-spike --provider mock --webhook-url http://localhost:8000/webhooks --webhook-signature wrong_secret

Options: valid (default), missing, corrupted, wrong_secret.

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Webhook Replay

Replay stored webhook payloads from any previous run. Useful for regression testing after code changes:

carbon replay <run_id> --webhook-url http://localhost:8000/webhooks

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CI/CD Integration

Use --ci to fail the build if any webhook returned 5xx or timed out:

carbon run dispute-spike --provider mock \
  --webhook-url http://localhost:8000/webhooks \
  --ci

Use --callback-url to POST a JSON run summary to your pipeline:

carbon run dispute-spike --provider mock \
  --webhook-url http://localhost:8000/webhooks \
  --callback-url http://localhost:8000/carbon/results \
  --ci

The callback payload includes pass/fail status, findings summary, and webhook delivery counts.

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Supported Payment Gateways

Carbon Layer generates provider-specific webhook payloads with correct signing for each gateway.

Provider	Webhook Format	Signing	CLI Flag
Mock	Razorpay-format	HMAC-SHA256	--provider mock
Razorpay	X-Razorpay-Signature	HMAC-SHA256	--provider razorpay
Stripe	Stripe-Signature: t=...,v1=...	HMAC-SHA256	--provider stripe
Cashfree	x-webhook-signature	Base64(HMAC-SHA256)	--provider cashfree
Juspay	Authorization: Basic ...	Basic Auth	--provider juspay

Razorpay

carbon run dispute-spike \
  --provider razorpay \
  --api-key your_test_key \
  --api-secret your_test_secret \
  --webhook-url https://your-app.com/webhooks

Or set RAZORPAY_API_KEY and RAZORPAY_API_SECRET as environment variables.

Stripe

carbon run dispute-spike \
  --provider stripe \
  --stripe-key sk_test_xxx \
  --webhook-url https://your-app.com/webhooks

Or set STRIPE_API_KEY as an environment variable.

Cashfree

carbon run dispute-spike \
  --provider cashfree \
  --cashfree-id your_app_id \
  --cashfree-secret your_secret_key \
  --webhook-url https://your-app.com/webhooks

Or set CASHFREE_CLIENT_ID and CASHFREE_CLIENT_SECRET as environment variables.

Juspay

carbon run dispute-spike \
  --provider juspay \
  --juspay-key your_api_key \
  --juspay-merchant-id your_merchant_id \
  --webhook-url https://your-app.com/webhooks

Or set JUSPAY_API_KEY and JUSPAY_MERCHANT_ID as environment variables.

Mock (no credentials needed)

carbon run dispute-spike --provider mock --webhook-url http://localhost:8000/webhooks

Mock mode simulates the full payment lifecycle locally. Use this if you don't have test credentials — all 11 scenarios work out of the box.

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Carbon Layer Pro (coming soon)

The open-source CLI covers 11 scenarios, 5 payment gateways, and webhook resilience testing. We're building a hosted Pro tier for teams that need more:

• Scheduled runs — run scenarios on a cron, get notified when your handlers regress
• PDF reports — export compliance-ready reports for audits and stakeholders
• Compliance dashboards — track webhook handler reliability over time
• Pro scenarios — RBI compliance checks, PCI readiness suite, 10k TPS load tests, multi-gateway failover, settlement reconciliation
• Team management — shared runs, role-based access, audit logs

The free CLI stays free and open-source (Apache 2.0). Pro is a separate hosted product.

Join the waitlist: pritom14.github.io/carbon-layer/waitlist

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License

Apache 2.0 — see LICENSE.