IMSI Decoder

What this IMSI decoder does

The IMSI (International Mobile Subscriber Identity) is the number that ties a SIM or eSIM profile to a subscription on a mobile network. Defined in 3GPP TS 23.003, it is at most 15 digits and breaks into three fixed-position fields: the three-digit MCC (Mobile Country Code), the two- or three-digit MNC (Mobile Network Code), and the remaining MSIN (Mobile Subscriber Identification Number). This tool takes the digits you paste, strips spaces and dashes, validates them, and shows each field separately along with a country name when the MCC is in its small built-in map.

Together the MCC and MNC form the PLMN identity of the home network — the same pair you see in IMSI catchers, roaming agreements, and the home-network field of a 5G SUCI. The MSIN is the operator-assigned serial that distinguishes one subscriber from another within that network.

When to use it

Reach for this when you are eyeballing a SIM provisioning record, a test profile from an eSIM/eUICC lab, an HLR/HSS export, or a signalling trace and you just want to confirm which country and network a given IMSI belongs to. It is handy for sanity-checking that a freshly written test SIM carries the MCC/MNC you intended, or for explaining the structure of subscriber identities in documentation. It is not a subscriber database and not a live operator directory.

Input and output

Input is a string of digits — paste with or without separators; only 0–9 survive cleaning. The decoder rejects non-digits and anything longer than 15 digits, and warns when the value is shorter than a full 15-digit IMSI. Because MNC length is region-dependent and is not carried in the IMSI itself, you choose how to split: Auto guesses 3 digits for NANP-style ranges (MCC 310–316 and a few others) and 2 digits elsewhere, or you can force 2-digit or 3-digit. Output lists the MCC (with a country name when known), the MNC digits, and the MSIN. The operator row is intentionally left unresolved.

Scope and honesty note

This decoder does not resolve the MNC to a named operator. There are thousands of MNC assignments and they change often, so a trustworthy lookup needs a maintained public MCC/MNC table rather than a hard-coded list that would quietly go stale. For operator resolution, consult a current public MCC/MNC reference such as the ITU/GSMA listings or community-maintained tables. The country map here is small and best-effort, not authoritative.

Common mistakes

• Confusing IMSI with ICCID. The ICCID is the SIM chip serial printed on the card; the IMSI is the subscription identity stored inside. Use the ICCID decoder for the former.
• Assuming a fixed MNC length. A 2-digit guess on a 3-digit MNC network shifts every later digit into the wrong field. Set the MNC length explicitly when you know the network.
• Expecting an operator name. This tool only maps the MCC to a country; it never names the carrier behind the MNC.
• Pasting a real IMSI. An IMSI is privacy-sensitive and can enable tracking. Work with dummy values; 5G even hides the IMSI inside the encrypted SUCI for this reason.

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