UK Sort Code Validation in Node.js — British Banking

1. What is a sort code?

A sort code is a 6-digit number used in the United Kingdom and Ireland to identify a specific bank branch. Sort codes are the UK equivalent of ABA routing numbers in the US or BSB codes in Australia — they tell the payment system which bank and branch an account belongs to.

Sort codes are required for virtually every type of UK domestic payment:

• BACS payments — Direct Debits, Direct Credits, standing orders (batch processing, 3-day cycle)
• Faster Payments — near-instant transfers up to £1,000,000 (most banks support this)
• CHAPS — same-day high-value payments, typically used for property purchases
• Cheque clearing — paper cheques processed through the Image Clearing System

If your application accepts UK bank account details — for payouts, Direct Debits, or account verification — you need to validate the sort code before initiating any transaction.

2. Sort code anatomy — the XX-XX-XX format

A sort code consists of three pairs of digits, conventionally written with hyphens:

3. How sort codes work — bank identification

Unlike ABA routing numbers or IBANs, UK sort codes do not include a check digit. Validation relies on matching the sort code against the official directory maintained by the Bankers' Automated Clearing Services (BACS).

4. Why sort code validation matters

5. The right solution

The IsValid Sort Code API validates the sort code format and returns the normalised and formatted representations in a single GET request. The response includes the raw 6-digit sort code and the hyphenated XX-XX-XX format.

Get your free API key at isvalid.dev. The free tier includes 100 calls per day — enough for most development and low-volume production use.

Full parameter reference and response schema: Sort Code Validation API docs →

6. Node.js code example

Using the IsValid SDK or the native fetch API.

import { createClient } from '@isvalid-dev/sdk';

const iv = createClient({ apiKey: process.env.ISVALID_API_KEY });

// ── Validate a sort code ────────────────────────────────────────────────────

const result = await iv.gb.sortCode('20-00-00');

if (!result.valid) {
  console.log('Invalid sort code');
} else {
  console.log(`Valid sort code: ${result.formatted}`); // "20-00-00"
  console.log(`Raw: ${result.sortCode}`);               // "200000"
}

// routes/bank-account.js (Express)
app.post('/bank-account/gb', async (req, res) => {
  const { sortCode, accountNumber, ...rest } = req.body;

  let sortCodeCheck;
  try {
    sortCodeCheck = await validateSortCode(sortCode);
  } catch {
    return res.status(502).json({ error: 'Sort code validation service unavailable' });
  }

  if (!sortCodeCheck.valid) {
    return res.status(400).json({ error: 'Invalid sort code' });
  }

  // Normalise the sort code for storage
  const normalised = sortCodeCheck.sortCode; // "200000"
  const display = sortCodeCheck.formatted;    // "20-00-00"

  console.log(`Verified sort code: ${display}`);

  await linkBankAccount({
    sortCode: normalised,
    accountNumber,
    ...rest,
  });

  res.json({ success: true, sortCode: display });
});

7. cURL example

Validate a sort code from the command line:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/gb/sort-code?value=20-00-00"

You can also pass the sort code without hyphens:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/gb/sort-code?value=200000"

Test with an invalid sort code:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/gb/sort-code?value=99-99-99"

8. Understanding the response

Valid sort code:

{
  "valid": true,
  "sortCode": "200000",
  "formatted": "20-00-00"
}

Invalid sort code:

{
  "valid": false
}

9. Edge cases to handle

// Handle building society accounts
function getBankDetailsForm(sortCode) {
  const result = validateSortCode(sortCode);
  // Building societies may need additional reference
  return {
    sortCode: result.formatted,
    requiresRollNumber: isBuildingSociety(sortCode),
  };
}