LEI Validation, Search & LOU Lookup in Node.js

1. What is a LEI?

A Legal Entity Identifier (LEI) is a 20-character alphanumeric code that uniquely identifies a legal entity participating in financial transactions. The standard is ISO 17442, managed by the Global Legal Entity Identifier Foundation (GLEIF).

LEIs are mandatory for:

• Derivatives reporting under EMIR and Dodd-Frank
• MiFID II transaction reporting in the EU
• Securities financing transactions (SFTR)
• Any entity trading on regulated markets

The GLEIF database contains over 2.3 million active LEIs, covering entities in 250+ jurisdictions.

2. LEI structure — the 20-character code

A LEI is exactly 20 characters: a 4-character LOU prefix + a 14-character entity identifier + 2 check digits.

All characters are uppercase alphanumeric (A-Z, 0-9). The LOU prefix is assigned by GLEIF to each Local Operating Unit — there are about 40 active LOUs worldwide.

3. The MOD-97 checksum

The LEI checksum uses the same MOD-97 algorithm as IBAN (ISO 7064):

Worked example: 784F5XWPLTWKTBV3E584

Each character is converted to its numeric equivalent. Digits stay as-is; letters become two-digit numbers (A=10, B=11, ..., Z=35):

• 784F → 7, 8, 4, 15 (F=15)
• 5XWPLTWKTBV3E5 → 5, 33, 32, 25, 21, 29, 32, 20, 29, 11, 31, 3, 14, 5
• 84 → 8, 4

The full digit string is: 7841553325212932202911313141584. Computing this number modulo 97 yields 1 — so the LEI is valid.

JavaScript implementation

function validateLeiChecksum(lei) {
  let digits = '';
  for (const ch of lei) {
    if (ch >= 'A' && ch <= 'Z') {
      digits += String(ch.charCodeAt(0) - 55); // A=10, B=11, ..., Z=35
    } else {
      digits += ch;
    }
  }

  // Block-wise modulo to avoid overflow
  let remainder = 0;
  for (const ch of digits) {
    remainder = (remainder * 10 + parseInt(ch, 10)) % 97;
  }

  return remainder === 1;
}

console.log(validateLeiChecksum('784F5XWPLTWKTBV3E584')); // true
console.log(validateLeiChecksum('784F5XWPLTWKTBV3E500')); // false

4. Three endpoints — validate, search, LOUs

The IsValid LEI API provides three endpoints that cover the full spectrum of LEI operations — from validating a single code to searching across 2.3 million entities:

Get your free API key at isvalid.dev. The free tier includes 100 calls per day with no credit card required.

Full parameter reference and response schema: LEI Validation API docs →

5. Endpoint 1: Validate a single LEI

The validate endpoint performs a multi-step verification chain:

Response — entity found (Goldman Sachs)

{
  "valid": true,
  "lei": "784F5XWPLTWKTBV3E584",
  "louCode": "784F",
  "checkDigits": "84",
  "found": true,
  "dataSource": "gleif-db",
  "entity": {
    "legalName": "GOLDMAN SACHS GROUP INC",
    "country": "US",
    "entityStatus": "ACTIVE",
    "registrationStatus": "ISSUED",
    "category": null,
    "initialRegistrationDate": "2012-06-06",
    "lastUpdate": "2024-08-14",
    "nextRenewal": "2025-08-14",
    "managingLou": "EVK05KS7XY1DEII3R011"
  },
  "lou": {
    "lei": "EVK05KS7XY1DEII3R011",
    "name": "Bloomberg Finance L.P.",
    "country": "US",
    "status": "ACTIVE"
  }
}

Response — invalid checksum

{
  "valid": false
}

Response — valid checksum but entity not found

{
  "valid": true,
  "lei": "784F5XWPLTWKTBV3E584",
  "louCode": "784F",
  "checkDigits": "84",
  "found": false,
  "dataSource": "gleif-api",
  "entity": null,
  "lou": null
}

6. Endpoint 2: Search entities by name

The search endpoint lets you find legal entities by name using fuzzy matching powered by PostgreSQL's pg_trgm extension. It supports filtering by country and entity status, with paginated results sorted by similarity score.

Parameters

Response

{
  "results": [
    {
      "lei": "784F5XWPLTWKTBV3E584",
      "legalName": "GOLDMAN SACHS GROUP INC",
      "country": "US",
      "entityStatus": "ACTIVE",
      "registrationStatus": "ISSUED",
      "category": null
    }
  ],
  "page": 1,
  "limit": 20,
  "total": 47
}

7. Endpoint 3: List all LOUs

No parameters needed. Returns all ~40 Local Operating Units — the organizations authorized by GLEIF to issue and maintain LEIs. Each LOU has a 4-character code that appears as the prefix of every LEI it issues.

Response

{
  "lous": [
    {
      "louCode": "784F",
      "lei": "EVK05KS7XY1DEII3R011",
      "name": "Bloomberg Finance L.P.",
      "country": "US",
      "status": "ACTIVE"
    }
  ],
  "total": 40
}

LOUs are responsible for the initial registration and annual renewal of LEIs. When a LEI lapses (the entity did not renew), it is the managing LOU that marks the registration as LAPSED. The LOUs endpoint is useful for building filter dropdowns, validating LOU prefixes in bulk, or understanding the geographic distribution of LEI issuance — most LOUs are concentrated in Europe and North America, but they serve entities globally.

8. Node.js code examples

Using the @isvalid-dev/sdk package or the built-in fetch API available in Node.js 18+. All three endpoints share the same authentication pattern.

Example 1: Validate a single LEI

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

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

const result = await iv.lei('784F5XWPLTWKTBV3E584');

if (!result.valid) {
  console.log('Invalid LEI');
} else {
  console.log('LEI     :', result.lei);
  console.log('Found   :', result.found);
  if (result.entity) {
    console.log('Name    :', result.entity.legalName);
    console.log('Country :', result.entity.country);
    console.log('Status  :', result.entity.entityStatus);
  }
}

Example 2: Search for entities

// Search for German banks
const banks = await iv.lei.search('deutsche bank', {
  country: 'DE',
  limit: 20,
});

console.log(`Found ${banks.total} results`);
banks.results.forEach(r => {
  console.log(`  ${r.lei} — ${r.legalName} (${r.country})`);
});

Example 3: List LOUs

const { lous, total } = await iv.lei.lous();

console.log(`${total} LOUs worldwide:`);
lous.forEach(l => {
  console.log(`  ${l.louCode} — ${l.name} (${l.country})`);
});

9. cURL examples

Validate a LEI (Goldman Sachs):

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/lei?value=784F5XWPLTWKTBV3E584"

Search by name (Goldman Sachs, US only):

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/lei/search?q=goldman%20sachs&country=US"

Search with pagination (page 2, 5 results per page):

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/lei/search?q=bank&limit=5&page=2"

List all LOUs:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/lei/lous"

10. Use cases — KYC, MiFID II, EMIR

LEI validation is a building block in many regulatory and compliance workflows. Here are the most common scenarios:

Node.js integration notes

In a TypeScript project, represent a validated LEI as a branded type so the compiler enforces that only checked values flow through your pipeline: type Lei = string & { readonly __brand: 'Lei' }. The IsValid SDK ships with complete TypeScript definitions for all response fields, which means your editor provides autocomplete on the parsed result — country codes, category names, registry data — without writing manual type declarations.

LEI validation often appears inside data ingestion pipelines: EDI feeds, supply-chain APIs, catalog imports, or financial data streams. In these contexts, validation happens at the boundary where external data enters your system. Model this as a transformation step: raw string in, validated branded type out. Use Promise.allSettled() to process batches and collect both valid and invalid results — invalid items can be quarantined for manual review without blocking the rest of the batch.

When LEI values arrive from user input or partner systems, normalise them before validation: trim surrounding whitespace, remove optional hyphens or spaces that some sources include for readability, and convert to the canonical case used by the relevant standard. Apply the same normalisation logic consistently across your codebase to prevent cache misses caused by formatting differences rather than value differences.

• Read process.env.ISVALID_API_KEY once at startup and store it in a module-level constant
• Use jest.mock() to stub the IsValid client in unit tests; CI pipelines should never make real API calls
• Log the full validation response at debug level — it often contains fields useful for debugging data quality issues
• For very high throughput, consider a local pre-filter that checks format with a regex before calling the API, reducing calls for obviously malformed inputs

When making HTTP calls to the IsValid API directly (without the SDK), the choice between fetch and axios is largely a matter of preference. The native fetch API is available in Node.js 18+ without any additional dependency and is sufficient for simple request/response flows. axios adds automatic JSON parsing, request/response interceptors, and a cleaner timeout API (axios.create({ timeout: 5000 })), which makes it easier to centralise the Authorization header and retry logic in one place. For high-throughput services that make many concurrent API calls, consider undici — the HTTP client underlying Node.js fetch — used directly for its connection pooling and lower overhead.