IBAN format · ST

Sao Tome and Principe IBAN format: 25 characters.

Sao Tome and Principe IBANs have 25 characters: the country code ST, two check digits and a 21-character BBAN, the national account number, laid out as 4!n4!n11!n2!n.

Sao Tome and Principe IBAN structure

ST23000100010051845310146

Country code: ST
Check digits: 23
Bank code: 0001
Branch code: 0001
Account: 0051845310146

Parts of a Sao Tome and Principe IBAN and their positions
Positions	Part	In the example
1–2	Country code	ST
3–4	Check digits	23
5–8	Bank code	0001
9–12	Branch code	0001
13–25	Account	0051845310146

The BBAN, segment by segment

The registry writes the BBAN in SWIFT notation: n is a digit, a an upper-case letter, c a letter or digit, and the ! means a fixed length. 4!n4!n11!n2!n reads:

The Sao Tome and Principe BBAN format, segment by segment
Positions	Notation	Holds	Example
5–8	4!n	4 digitsBank code	0001
9–12	4!n	4 digitsBranch code	0001
13–23	11!n	11 digits	00518453101
24–25	2!n	2 digits	46

Sao Tome and Principe IBAN example

ST23 0001 0001 0051 8453 1014 6 is the sample the SWIFT IBAN Registry publishes for Sao Tome and Principe: a well-formed IBAN for showing the format, not a real account. Written electronically it has no spaces (ST23000100010051845310146); on paper it is printed in groups of four.

Its check digits, worked through with ISO 7064 mod 97-10:

Move the country code and check digits to the end
000100010051845310146ST23
Replace each letter with two digits (A = 10 … Z = 35)
S = 28, T = 29
000100010051845310146282923
Divide that number by 97 and keep the remainder
Remainder 1. A valid IBAN always leaves 1, so the check digits are right.
Where the check digits come from
Put 00 in their place (ST00…), repeat steps 1–3: remainder 75. The check digits are 98 − 75 = 23.

SEPA

Sao Tome and Principe is not in the Single Euro Payments Area, so SEPA credit transfers and direct debits don’t reach ST IBANs.

What the format can and can’t tell you

Valid means the structure and check digits are right — not that the account exists or can receive payments.
National check digits inside the BBAN (e.g. the French RIB key, or the Spanish, Belgian and Italian CIN digits) are not verified.
Bank and branch codes are read from their positions; they are not looked up in a bank directory.

Check ST IBANs from code or an AI agent

REST · GET · no key

curl -s 'https://payopskit.com/api/v1/iban/ST23000100010051845310146'

MCP · tools/call · validate_iban

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "validate_iban",
    "arguments": {
      "iban": "ST23000100010051845310146"
    }
  }
}

Response (JSON)

{
  "input": "ST23000100010051845310146",
  "iban": "ST23000100010051845310146",
  "print": "ST23 0001 0001 0051 8453 1014 6",
  "valid": true,
  "country": {
    "code": "ST",
    "name": "Sao Tome and Principe",
    "sepa": false,
    "sepaNote": null
  },
  "checkDigits": "23",
  "expectedCheckDigits": "23",
  "length": {
    "actual": 25,
    "expected": 25
  },
  "bban": "000100010051845310146",
  "bbanFormat": "4!n4!n11!n2!n",
  "bankCode": "0001",
  "branchCode": "0001",
  "parts": [
    {
      "label": "Country code",
      "value": "ST",
      "start": 0,
      "end": 2,
      "kind": "country"
    },
    {
      "label": "Check digits",
      "value": "23",
      "start": 2,
      "end": 4,
      "kind": "check"
    },
    {
      "label": "Bank code",
      "value": "0001",
      "start": 4,
      "end": 8,
      "kind": "bank"
    },
    {
      "label": "Branch code",
      "value": "0001",
      "start": 8,
      "end": 12,
      "kind": "branch"
    },
    {
      "label": "Account",
      "value": "0051845310146",
      "start": 12,
      "end": 25,
      "kind": "account"
    }
  ],
  "checks": {
    "characters": true,
    "country": true,
    "length": true,
    "bbanFormat": true,
    "checksum": true
  },
  "errors": [],
  "notes": [
    "Valid means the structure and check digits are right — not that the account exists or can receive payments.",
    "National check digits inside the BBAN (e.g. the French RIB key, or the Spanish, Belgian and Italian CIN digits) are not verified."
  ]
}

The MCP server is at /mcp (Streamable HTTP, no key); the API and MCP docs show how to connect Claude, Cursor or VS Code.

From a national account number: GET /api/v1/iban/check-digits?country=ST&bban=… or the MCP tool compute_iban_check_digits computes the check digits and the whole IBAN.

Other 25-character IBANs

The same length doesn’t mean the same structure: compare the BBAN formats. All IBAN formats and lengths

Source: the SWIFT IBAN Registry (ISO 13616), transcribed and checked against each country’s registry example; the positions of bank and branch codes are given only where the registry’s are well established. The SWIFT IBAN Registry is the authority. Informational only.