CUSIP / ISIN / SEDOL / FIGI Validator

About this tool

This tool validates and generates check digits for four financial security identifier systems. It also includes a bundled CUSIP↔ISIN cross-walk of 16 well-known US equity mappings. All computation runs in your browser — no data leaves this page and no network requests are made.

The four identifier systems

• CUSIP — 9 chars, North American. Assigned by CUSIP Global Services (FactSet). Algorithm: Mod-10 with letter-to-number mapping (A=10..Z=35), doubling body positions i=1,3,5,7.
• ISIN — 12 chars, international (ISO 6166). Starts with a 2-letter country code. Algorithm: Luhn mod-10 on the alphanumeric expansion.
• SEDOL — 7 chars, UK. Algorithm: fixed-weight sum with weights 1,3,1,7,3,9,1 (check digit included in the weighted sum).
• FIGI — 12 chars, global (OMG / Bloomberg). Starts with G. Algorithm: Luhn mod-10 on the alphanumeric expansion.

What the check digit detects

A check digit detects single-character transcription errors — most typos and copy-paste mistakes produce a different check digit, so the tool can flag them. The check digit does NOT verify that the security exists, is correctly assigned to the issuer you think, or is a current instrument. It is a structure-only check.

The "Suggest fix" feature on an Invalid result runs a brute-force search: for each position in the body, it tries every possible character and keeps the substitutions that produce a matching check digit. With low-entropy systems (SEDOL in particular) there may be multiple valid corrections; the tool shows the lex-smallest plus a count of alternatives.

Cross-walk (CUSIP↔ISIN)

The cross-walk ships with 16 verified mappings sourced from Wikipedia (CUSIP article Examples and company article infoboxes), Wikidata property P946, and SEC EDGAR company submissions. The cross-walk is fully local — no external API is consulted. This is a deliberate choice: the free OpenFIGI API does not return ISIN or CUSIP values (per their own licensing policy) and blocks browser-direct calls via CORS. A future enhancement could add a Cloudflare Worker proxy to enable live cross-walks; v1 ships with the bundled sample only.

Format error vs. check-digit mismatch

The tool distinguishes two failure modes:

• Unparseable — the input doesn't match the chosen system's grammar (wrong length, character class, or prefix). The error message names the specific rule.
• Invalid — the input parses but the check digit doesn't match. A "Suggest fix" appears below.

Educational only. Not investment advice.

All computation runs in the browser. No identifier input is sent to any server. The tool does not maintain a security master database and does not verify that an identifier is actually assigned. Verify any trading decision with your broker before execution.