Definition
A short code is a short phone number, usually 3–8 digits, that businesses use to send and receive SMS at volume, for example for opt-ins, voting, OTPs and two-way campaigns.
Short codes are assigned at national level, either by operators or a national short code administrator, so a short code works only within its country. They are not E.164 international numbers.
Because short codes are dedicated to A2P use and vetted by operators, they usually support higher throughput and two-way messaging. Recipients can text a keyword such as JOIN or STOP to the code.
Obtaining a short code takes time and often involves a lease fee, a use-case description and operator approval. Shared short codes, where several businesses use one code with different keywords, are cheaper but give less control.
For international campaigns, a business needs a separate short code or another sender type in each country. Many businesses combine an alphanumeric sender ID for outbound alerts with a short code or long code for replies.
Example
Text JOIN to 4567 to receive weekly offers. Reply STOP to unsubscribe.