How to validate a Brazilian CPF or CNPJ (including alphanumeric CNPJ)

How the check digit works

CPF (11 digits, 2 check digits, mod 11):

1. Multiply the first 9 digits by 10, 9, …, 2; r = sum mod 11; first digit = 0 if r < 2, else 11 − r.
2. Append it and multiply the 10 digits by 11, 10, …, 2; same rule for the second digit.
3. All-repeated numbers (e.g. 111.111.111-11) are invalid.

CNPJ (14 characters; since IN RFB 2.229/2024 the first 12 may be letters):

1. Value of each character = ASCII code − 48 (digits 0–9, A = 17 … Z = 42).
2. First digit: weights 5,4,3,2,9,8,7,6,5,4,3,2 over 12 characters; second: 6,5,4,3,2,9,8,7,6,5,4,3,2 over 13.
3. Same rule: 0 if sum mod 11 < 2, else 11 − (sum mod 11). The two check digits are always numeric.

Validate with the API

Direct use is free: 50 requests per IP per day, no signup. Endpoints: POST /validate, POST /batch, GET /generate/{doc_type} (for testing only: synthetic data, not real identities).

curl

curl -X POST "https://validalatam.ia-latam.app/validate" -H "Content-Type: application/json" \
  -d '{"type":"BR_CPF","value":"202.876.353-17"}'

curl -X POST "https://validalatam.ia-latam.app/validate" -H "Content-Type: application/json" \
  -d '{"type":"BR_CNPJ","value":"95.813.404/0001-00"}'

# synthetic test data only / solo para pruebas
curl "https://validalatam.ia-latam.app/generate/BR_CPF"

Python

import requests

BASE = "https://validalatam.ia-latam.app"

r = requests.post(f"{BASE}/validate", json={"type": "BR_CPF", "value": "202.876.353-17"})
print(r.json()["valid"], r.json()["formatted"])

r = requests.post(f"{BASE}/validate", json={"type": "BR_CNPJ", "value": "95.813.404/0001-00"})
print(r.json()["valid"], r.json()["formatted"])

Real API response (synthetic value from /generate)

202.876.353-17 (BR_CPF):

{"valid":true,"type":"BR_CPF","country":"BR","input":"202.876.353-17","normalized":"20287635317","formatted":"202.876.353-17","error":null,"details":{"fiscal_region":3}}

95.813.404/0001-00 (BR_CNPJ):

{"valid":true,"type":"BR_CNPJ","country":"BR","input":"95.813.404/0001-00","normalized":"95813404000100","formatted":"95.813.404/0001-00","error":null,"details":{"branch":"0001","alphanumeric":false}}

Plans

For AI assistants (MCP)

pip install validalatam-mcp

github.com/elmatis172/validalatam-mcp

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