API for Developers & Accountants | FilingFox

Why Build with FilingFox?

📋

All Return Types

Submit VAT (MTD), Self Assessment (SA100 + schedules), and Corporation Tax (CT600 + iXBRL) through a single, unified API.

🔒

HMRC Recognised

We handle the complexity of HMRC integration, fraud prevention headers, and MTD compliance. You just send the data.

⚡

Simple REST API

Clean, well-documented endpoints. JSON in, JSON out. Get started in minutes with our SDKs for Node.js, Python, and PHP.

🔔

Webhooks

Real-time notifications for submission status, HMRC responses, and deadline reminders. No polling required.

📊

Bulk Operations

Submit hundreds of returns efficiently. Perfect for accountancy practices managing multiple clients.

🏷️

White Label

Embed FilingFox functionality into your own application. Your brand, our infrastructure.

Simple Integration

                    
                    
                    
                    submit-vat.js
                

const response = await filingfox.vat.submit({
  vrn: "123456789",
  periodKey: "24A1",
  vatDueSales: 15000.00,
  vatDueAcquisitions: 0.00,
  totalVatDue: 15000.00,
  vatReclaimedCurrPeriod: 3500.00,
  netVatDue: 11500.00,
  totalValueSalesExVAT: 75000,
  totalValuePurchasesExVAT: 17500,
  totalValueGoodsSuppliedExVAT: 0,
  totalAcquisitionsExVAT: 0
});

// Response
{
  status: "accepted",
  processingDate: "2025-04-07T14:32:00Z",
  formBundleNumber: "119234567891",
  paymentIndicator: "DD",
  chargeRefNumber: "XD002750002155"
}
                

Built For

🏢

Accountancy Practices

Integrate with your practice management software. Submit returns for all your clients from a single dashboard or automated workflow.

💻

Software Developers

Building accounting, invoicing, or business software? Add UK tax filing as a feature without the complexity of HMRC integration.

🏦

Enterprise & Fintech

Large-scale tax operations, embedded finance products, or neobank integrations. Volume pricing and dedicated support available.

Transparent API Pricing

Pay only for what you use. No monthly minimums. Volume discounts available.

£4.99 per VAT return

£29.99 per SA100

£59.99 per CT600

Custom Enterprise

* Pricing is preliminary and subject to change. Final pricing will be announced at launch.

Frequently Asked Questions

When will the API be available?

We're targeting Q2 2025 for public beta. Waitlist members will receive early access and the opportunity to provide feedback during development.

Do I need to be HMRC-recognised to use the API?

No. FilingFox is the recognised software provider. Your submissions go through our HMRC-approved infrastructure, so you don't need separate HMRC recognition.

How does client authorisation work?

For accountants filing on behalf of clients, each client grants authorisation via their HMRC Government Gateway. We provide an OAuth flow and hosted authorisation page you can embed or link to.

Is there a sandbox environment?

Yes. You'll have access to a full sandbox environment that mirrors HMRC's test APIs. Test your integration without affecting live tax records.

What about iXBRL for CT600?

We handle iXBRL generation automatically. Send us your accounts data in JSON format, and we'll generate the compliant iXBRL accounts and CT600 for submission.

Can I white-label the service?

Yes. Enterprise plans include white-label options where users see your brand throughout the process. Contact us for details.

What support is available?

All plans include email support and comprehensive documentation. Higher tiers include dedicated account managers, priority support, and integration assistance.

FilingFox API for Developers & Accountants