SEDOL Validation in Node.js

1. What is a SEDOL?

A SEDOL (Stock Exchange Daily Official List) is a 7-character alphanumeric identifier assigned by the London Stock Exchange Group (LSEG) to securities listed on UK and Irish exchanges, as well as a large number of internationally traded instruments. First introduced in 1979, SEDOLs are the primary security identifier in the UK financial infrastructure.

CREST — the central securities depository for UK and Irish equities and bonds, operated by Euroclear — uses SEDOLs as a key reference in settlement instructions. The UK's Financial Conduct Authority (FCA) references SEDOLs in transaction reporting under MiFIR (Markets in Financial Instruments Regulation), alongside ISINs.

SEDOLs cover equities, gilts (UK government bonds), corporate bonds, exchange-traded funds, and investment trusts. The SEDOL Masterfile — maintained by LSEG — contains over 100 million securities from markets worldwide, making SEDOL a global identifier despite its UK origins.

2. SEDOL anatomy

Every SEDOL is exactly 7 characters long, divided into two parts:

Modern SEDOLs (issued after 2004) use only consonants — vowels (A, E, I, O, U) are excluded from the base code to avoid ambiguity when codes are spoken or handwritten. Older SEDOLs allocated before 2004 may contain vowels and remain valid.

Some well-known examples:

3. The check digit algorithm

The SEDOL check digit uses a weighted modulo-10 algorithm — simpler than the CUSIP modified Luhn, but with its own specific weight sequence and character mapping. The character values are:

The fixed position weights applied to the first 6 characters are:

The algorithm is:

1. For each of the first 6 characters, convert it to its numeric value using the mapping above.
2. Multiply each value by the corresponding weight from the table above.
3. Sum all 6 weighted values to get S.
4. The check digit is (10 - (S % 10)) % 10.

Example — BP PLC (079805):

Check digit = (10 - (131 % 10)) % 10 = (10 - 1) % 10 = 9. Full SEDOL: 0798059 ✓

Here is what a naive Node.js implementation looks like:

// sedolCheck.js — naive implementation (format + check digit only)

/**
 * Map a SEDOL character to its numeric value.
 * 0-9 = 0-9, A-Z = 10-35
 */
function charValue(ch) {
  const code = ch.charCodeAt(0);
  if (code >= 48 && code <= 57) return code - 48;   // '0'-'9'
  if (code >= 65 && code <= 90) return code - 55;   // 'A'-'Z'
  throw new Error(`Invalid SEDOL character: ${ch}`);
}

const WEIGHTS = [1, 3, 1, 7, 3, 9];

/**
 * Compute the SEDOL check digit.
 * Input: the first 6 characters of a SEDOL.
 * Returns: the expected check digit (0-9).
 */
function computeCheckDigit(base6) {
  let sum = 0;
  for (let i = 0; i < 6; i++) {
    sum += charValue(base6[i]) * WEIGHTS[i];
  }
  return (10 - (sum % 10)) % 10;
}

const SEDOL_RE = /^[A-Z0-9]{6}[0-9]$/;

function validateSedolFormat(sedol) {
  sedol = sedol.replace(/\s/g, '').toUpperCase();

  if (sedol.length !== 7 || !SEDOL_RE.test(sedol)) {
    return { valid: false, reason: 'format' };
  }

  const expected = computeCheckDigit(sedol.slice(0, 6));
  const actual = Number(sedol[6]);

  if (expected !== actual) {
    return { valid: false, reason: 'check_digit' };
  }

  return {
    valid: true,
    sedol,
    checkDigit: sedol[6],
  };
}

// ── Examples ──────────────────────────────────────────────────────────────────
console.log(validateSedolFormat('0798059'));   // valid — BP PLC
console.log(validateSedolFormat('0540528'));   // valid — HSBC Holdings
console.log(validateSedolFormat('0798051'));   // invalid check digit
console.log(validateSedolFormat('07980'));     // invalid format (too short)

4. Why manual validation isn't enough

5. The right solution: one API call

Instead of implementing the check digit algorithm yourself and trying to maintain a reference dataset, use the IsValid SEDOL API. A single GET /v0/sedol request handles format validation, check digit verification, and instrument lookup via OpenFIGI — all in one call.

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: SEDOL Validation API docs →

6. Node.js code example

Using the @isvalid-dev/sdk package or the native fetch API (Node 18+).

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

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

// ── Example usage ─────────────────────────────────────────────────────────────

const result = await iv.sedol('0798059');  // BP PLC

if (!result.valid) {
  console.log('Invalid SEDOL: failed format or check digit');
} else {
  console.log(`SEDOL       : ${result.sedol}`);
  console.log(`Check digit : ${result.checkDigit}`);
  if (result.found) {
    console.log(`Name        : ${result.name}`);
    console.log(`Ticker      : ${result.ticker}`);
    console.log(`Exchange    : ${result.exchCode}`);
    console.log(`FIGI        : ${result.figi}`);
    console.log(`Sector      : ${result.marketSector}`);
  }
}

Expected output for 0798059:

SEDOL       : 0798059
Check digit : 9
Name        : BP PLC
Ticker      : BP/
Exchange    : LN
FIGI        : BBG000BT4FC2
Sector      : Equity

// routes/securities.js (Express)
app.get('/securities/validate-sedol', async (req, res) => {
  const { sedol } = req.query;

  if (!sedol) {
    return res.status(400).json({ error: 'Missing sedol parameter' });
  }

  let result;
  try {
    result = await validateSedol(sedol);
  } catch {
    return res.status(502).json({ error: 'SEDOL validation service unavailable' });
  }

  if (!result.valid) {
    return res.status(400).json({ error: 'Invalid SEDOL', sedol });
  }

  res.json({
    sedol: result.sedol,
    checkDigit: result.checkDigit,
    found: result.found ?? null,
    name: result.name ?? null,
    ticker: result.ticker ?? null,
    exchCode: result.exchCode ?? null,
    figi: result.figi ?? null,
  });
});

7. cURL example

Validate a SEDOL from the command line:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/sedol?value=0798059"

HSBC Holdings:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/sedol?value=0540528"

Invalid check digit — the API returns valid: false:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/sedol?value=0798051"

8. Understanding the response

Response for a valid SEDOL found in OpenFIGI:

{
  "valid": true,
  "sedol": "0798059",
  "checkDigit": "9",
  "found": true,
  "dataSource": "openfigi",
  "name": "BP PLC",
  "ticker": "BP/",
  "exchCode": "LN",
  "securityType": "Common Stock",
  "marketSector": "Equity",
  "figi": "BBG000BT4FC2",
  "compositeFIGI": "BBG000BT4FC2"
}

Response for a valid SEDOL not found in OpenFIGI:

{
  "valid": true,
  "sedol": "0798059",
  "checkDigit": "9",
  "found": false
}

Response for an invalid SEDOL:

{
  "valid": false
}

9. Edge cases to handle

10. Summary

For cross-referencing, see also:

• ISIN validation — ISINs embed SEDOLs for GB-prefixed codes
• CUSIP validation — the North American equivalent
• LEI validation — identifies the instrument issuer