Sandbox Portal

A self-service sandbox where developers register, experiment, and build against Monument's APIs using synthetic data — without touching live systems. Every response mirrors production structure exactly.

Data Sets5

Accounts505

Transactions30K+

Endpoints78

Auto-ResetDaily

Developer Onboarding Journey

Self-Service Registration

Developer signs up, creates an organisation, accepts T&Cs. Automated email verification.

API Key Provisioning

Sandbox keys auto-generated (mtl_sk_sandbox_*). Production keys require manual approval.

Sandbox Testing

Build and test against synthetic data. Full request/response parity with production.

Production Promotion

Compliance review, contract signing, production keys issued. Zero code changes required.

Sandbox Endpoints

All 78 production endpoints are available in sandbox. These 4 showcase full request/response structures.

POST/v1/paymentsSANDBOX

cURL Command

curl -X POST "https://sandbox.api.monument.tech/v1/payments" \
  -H "Authorization: Bearer mtl_sk_sandbox_4eC39HqLyjWDarjtT1zdp7dc" \
  -H "Content-Type: application/json" \
  -H "Monument-Version: 2026-02-01" \
  -H "Idempotency-Key: idem_cs335up8" \
  -d '...'

Request Body (application/json)

{
  "amount": 1500.00,
  "currency": "GBP",
  "source_account_id": "acc_sandbox_4eC39HqLy",
  "destination": {
    "type": "uk_bank_account",
    "sort_code": "20-00-00",
    "account_number": "55779911",
    "name": "Jane Smith"
  },
  "rail": "fps",
  "reference": "Invoice INV-2026-001",
  "idempotency_key": "idem_pay_8kL2mN4p",
  "metadata": {
    "invoice_id": "inv_001",
    "department": "treasury"
  }
}

Innovative Sandbox Capabilities

Beyond standard sandboxing — features that accelerate developer adoption and reduce production incidents.

Event-Sourced Time Travel

Replay and debug any transaction flow by rewinding sandbox state to any point in time. Developers can inspect intermediate states, retry failed steps, and understand exactly how the API processes complex workflows.

Chaos Engineering Mode

Simulate failures, latency spikes, timeout scenarios, and edge cases to test resilience before going live. Configurable via X-Sandbox-Chaos header: network_delay, service_down, partial_failure, rate_limit_exceeded.

Consumer-Driven Contract Testing

Developers define expected request/response contracts. The sandbox validates that production behaviour matches exactly. Any breaking change is flagged before deployment, preventing integration failures.

Time Simulation

Fast-forward sandbox time to test interest accrual, statement generation, payment settlement, and card expiry scenarios. POST /v1/sandbox/time-travel with target_date parameter.

Compliance Simulation

Test KYC/AML workflows with configurable outcomes: verified, failed, pending_review, sanctions_hit. Simulate PEP matches, adverse media hits, and document verification failures.

Error Scenario Library

Pre-built error scenarios for every endpoint: insufficient_funds, account_frozen, payment_rejected, kyc_failed, rate_limited. Triggered via X-Sandbox-Scenario header.