---
title: "ISIN"
description: "An ISIN is the 12-character ISO 6166 code that uniquely identifies a security worldwide; each fund share class has its own, which makes it the natural key for fund data."
canonical: https://fundfactsapi.com/glossary/isin
published: 2026-09-04
updated: 2026-09-04
publisher: FundFacts API
---

# ISIN (International Securities Identification Number, ISO 6166, ISIN code)

> An ISIN is the 12-character ISO 6166 code that uniquely identifies a security worldwide; each fund share class has its own, which makes it the natural key for fund data.

## Definition

An **International Securities Identification Number (ISIN)** is a 12-character code defined by ISO 6166 and allocated by each country's national numbering agency. It is made up of a two-letter country prefix, a nine-character national identifier and a check digit computed with the Luhn algorithm. `IE00B4L5Y983` identifies exactly one share class of one ETF: the iShares Core MSCI World UCITS ETF USD (Acc). The distributing class, a hedged class or the same strategy from a different fund house each have their own ISIN.

## Why it matters

Tickers change with the exchange and [CUSIP](https://fundfactsapi.com/glossary/cusip), [SEDOL](https://fundfactsapi.com/glossary/sedol) and [WKN](https://fundfactsapi.com/glossary/wkn) are national, but the ISIN is global and printed on every factsheet, KID, contract note and custody statement. It is the identifier regulators use in transaction reporting and the one every fund data API accepts as input. Storing ISINs as your primary key avoids most reconciliation problems.

## In the API

The ISIN is the only input: `GET /api/v1/funds/{isin}`. The response echoes it at top level and may include ISINs of underlying holdings inside `topHoldings`. Example values:

```json
{
  "isin": "IE00B3RBWM25",
  "name": "Vanguard FTSE All-World UCITS ETF USD Dist",
  "cached": true,
  "data": { "securityType": "ETF" }
}
```

A malformed code returns `400 invalid_isin`; a well-formed code that does not correspond to a fund returns `404 fund_not_found`.

## Common pitfalls

Validate format and check digit client-side before spending a request. Normalise to upper case and strip whitespace. Never treat the ISIN as a number: letters may appear in positions 3 to 11, and leading zeros are significant.

## About FundFacts API

FundFacts turns any fund or ETF ISIN into one dated factsheet (fees and KID costs, the 1–7 risk indicator, holdings, sector and country exposure, returns) read from the fund house's own documents: as a client-ready PDF under your firm's name for advisers and wealth managers, as JSON through its API for developers, or inside ChatGPT and Claude through its MCP server.

FundFacts works inside ChatGPT and Claude as a connector (a remote MCP server): ask about any fund or ETF by ISIN, ticker or name and the assistant answers from FundFacts' dated figures, fees, risk, holdings, exposure and returns, with fund cards, side-by-side comparisons, holdings overlap and portfolio look-through.

- Free API key, no card: https://fundfactsapi.com/signup
- Documentation: https://fundfactsapi.com/docs (OpenAPI: https://fundfactsapi.com/openapi.json)
- MCP server: https://fundfactsapi.com/api/mcp (set-up for every client: https://fundfactsapi.com/mcp-server)
- Pricing: https://fundfactsapi.com/pricing
- Site index for AI assistants: https://fundfactsapi.com/llms.txt
- Informational data, not investment advice.