Build on Fylix.
Programmatic access to every part of the platform. OAuth 2.0, REST + JSON, webhooks, and SDKs in TypeScript, Python, and Go.
# Fetch tax return summary
curl -X GET https://api.fylix.co.uk/v1/tax-returns/2025 \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json"
# Response
{
"id": "tr_abc123",
"tax_year": "2024-25",
"status": "submitted",
"total_income": 75000.00,
"total_expenses": 12500.00,
"tax_liability": 15750.00,
"submitted_at": "2026-01-31T23:59:00Z"
}API at a glance
Everything modern integrations need.
Authentication you trust
Access + refresh tokens for long-lived integrations. Per-tenant scoping built in.
Fair, per-key quotas
1,000 req/hour on Pro; enterprise plans available for higher limits.
Real-time events
Filing status, submission confirmations, and per-row events delivered in under 1s.
Base URL
https://api.fylix.co.uk/v1All API requests go to this base URL with the appropriate endpoint path.
Authentication
Authorization: Bearer YOUR_API_KEYInclude your API key in the Authorization header for every request.
Endpoints
Coverage across every surface.
Each resource ships with paginated list, single-fetch, write, and delete endpoints — typed in OpenAPI 3.1.
Tax returns
Create, update, and submit self-assessment tax returns programmatically.
Transactions
Import, categorise, and manage income and expense transactions.
Properties
Manage rental properties and associated income records.
Clients
Client management endpoints for accountancy practices.
Reports
Generate tax reports, analytics, and export financial data.
Webhooks
React to filing events in real time.
// Verify and parse a webhook payload
import { verify } from "@fylix/webhooks"
export async function POST(req: Request) {
const sig = req.headers.get("x-fylix-signature")
const raw = await req.text()
const event = verify(raw, sig, process.env.FYLIX_WEBHOOK_SECRET!)
switch (event.type) {
case "tax_return.submitted":
// notify your system
break
case "transaction.categorised":
// refresh your dashboards
break
}
return new Response("ok")
}Rate limits
- Free: 100 requests/hour
- Professional: 1,000 requests/hour
- Enterprise: 10,000+ requests/hour
Rate limits are applied per API key. Contact us for custom limits.
Full reference
This is a high-level overview. For complete schemas, error codes, and advanced features, visit the developer portal.
Ready to start building?
Get your API key today and ship your integration this week.