Tracking Code Validator

How does the tracking code work?

Correios use the AA123456789BR pattern, 13 characters in all: 2 service-prefix letters (for instance, BR for PAC, JT for Sedex), 9 digits for the label number and 2 closing letters with the country code, usually BR.

What we check here is only the format; there's no status lookup against the Correios API. To actually follow a delivery, head to the official Correios site.

Everything is checked right in your browser.

UPU S10: the universal standard behind postal tracking codes

Every Correios tracking code follows UPU S10, a standard published by the Universal Postal Union (Bern, Switzerland) and adopted by all 192 member countries. The format is strict: LL 9 digits LL — two letters identifying the service class, nine digits (eight serial + one check digit), and two letters for the destination country using ISO 3166-1 alpha-2 (BR for Brazil, US for the United States, DE for Germany).

The point of S10 is interoperability: a single number must work across Correios, USPS, Royal Mail, Deutsche Post and Japan Post systems. Without it, every customs hand-off and last-mile transfer would require manual rekey. S10 also defines barcode symbology (Code 128), the human-readable layout printed on labels and the mandatory check-digit position.

The mod-11 check digit algorithm

The 8th digit of the numeric block is a check digit computed from the previous 7 using a weighted mod-11 scheme. The weights, applied in order, are 8, 6, 4, 2, 3, 5, 9, 7. Procedure:

• Multiply each of the first 7 digits by its corresponding weight.
• Sum the products and compute sum mod 11.
• Subtract from 11. If the result is 10, the check digit is 0; if 11, it is 5; otherwise it is the subtraction itself.

code   = "LB 4 7 8 5 8 6 1 _ BR"
digits = [4, 7, 8, 5, 8, 6, 1]
weights= [8, 6, 4, 2, 3, 5, 9]
sum    = 32+42+32+10+24+30+9 = 179
179 mod 11 = 3
11 - 3 = 8  -> check digit = 8

Common Correios service prefixes

• LB: international simple letter post.
• PJ: international EMS / Sedex Mundi.
• RA, RB, RL: domestic registered letter.
• JT, JU: domestic Sedex (express).
• AR: aviso de recebimento (return receipt add-on).
• DU: debito automatico (auto-debit notice).

Sedex 12 typically uses the JT prefix while PAC tends to use OE or OY. Knowing the prefix lets a CRM auto-route the parcel to the right SLA bucket without parsing the tracking page.

Real-world use cases

E-commerce platforms (Magazine Luiza, Americanas, Mercado Livre) validate codes the moment a label is printed, before saving them to the customer-facing order page. This prevents a typo from triggering hours of "code not found" support tickets. CRM tools like Octadesk or Zendesk use the same validator at the bot level: if the customer pastes a malformed code, the bot answers immediately instead of opening a ticket.

Aggregator APIs and the post-SRO landscape

The Correios SRO (Sistema de Rastreamento de Objetos) public API was discontinued and replaced by a paid corporate channel that requires a contract. The pragmatic alternatives are:

• 17track.net: multi-carrier aggregator (Correios, Loggi, FedEx, DHL, USPS, China Post). Free tier + paid API.
• BrasilAPI: community endpoint that scrapes the Correios web tracker. Best-effort, not for SLAs.
• Melhor Envio: Brazilian shipping marketplace with a unified tracking webhook.
• Frenet, Kangu: enterprise shipping APIs with carrier-side tracking.

Note that Brazilian last-mile competitors — Loggi, Total Express, Mercado Envios, J&T Express, Jadlog — each use proprietary code formats and are not bound by UPU S10. Validating their codes requires per-carrier regex or BIN-style lookup tables.