What is a short code in SMS?
A short code is a five or six digit phone number used to send and receive text messages at high volume. You have probably seen one on a poster or screen: "Text VOTE to 12345". Because the number is short, people remember it, and because carriers vet and approve each one, short codes can send far faster than ordinary phone numbers.
This guide explains how short codes work, how they compare with the alternatives, what the application involves and how to decide whether you need one. If you are still choosing between sender types, our guide to SMS sender IDs covers the other options.
How short codes work
A short code is not bought like a phone number. It is leased from a registry that manages the numbering plan, and then provisioned onto each mobile carrier, which reviews the programme before switching it on. Once live, messages sent from the code travel on dedicated routes built for volume. See the background on short codes and premium SMS.
| Feature | What it means in practice |
|---|---|
| Length | Five or six digits, depending on the country and range |
| Ownership | Leased, not purchased; renewed periodically |
| Approval | Each programme is reviewed by the carriers before launch |
| Direction | Two-way: send messages and receive keyword replies |
| Speed | Built for the highest throughput of any sender type |
| Audience | Mainly the US, Canada and some other markets |
Short codes can be dedicated, used by one brand only, or shared, though shared codes have been phased out in many markets because they make it hard to track who sent what. A dedicated code protects your reputation from other senders.
Short code vs long code vs toll-free
| Short code | Toll-free | Long code (10DLC) | |
|---|---|---|---|
| Digits | 5 or 6 | 10 (800-type) | 10 (local) |
| Set-up time | Several weeks | Days to weeks | Days to a couple of weeks |
| Throughput | Highest | Mid to high | Depends on trust score |
| Relative cost | Highest | Moderate | Lowest |
| Memorability | Best | Good | Low |
| Best for | Mass campaigns and alerts | Support and national brands | Most businesses |
Our guide to 10DLC explains the long-code route in the US, and A2P messaging covers why registration exists at all.
When a short code is worth it
- Very large sends. If you must reach hundreds of thousands of people within minutes, only a short code has the throughput.
- Time-critical alerts. Emergency notices, flash sales and live event updates cannot queue for an hour.
- Keyword programmes. Donations, contests, polls and sign-ups that people trigger by texting a word to a memorable number.
- High-value codes. One-time passcodes for very large user bases, where delivery speed has a direct effect on conversion.
Start smaller if you can. Many brands begin with a registered local number or a verified toll-free number, prove the programme works, then move to a short code when volume demands it.
How to get a short code
- Decide dedicated and the digits you want. Check availability in the registry. Vanity numbers that spell a word cost more.
- Write the programme description. Say what the messages are for, how often you send them and who receives them.
- Document the opt-in. Show every place people agree, with the exact consent wording and a link to your terms and privacy policy.
- Prepare the message flow. Provide sample messages, the welcome message, and your STOP and HELP replies.
- Submit and wait. Your provider submits the application. Carriers may ask questions or require changes.
- Test and launch. After each carrier activates it, test on every network before sending to customers.
Rules differ by country and change. Our country rules guide is the place to check, and the compliance overview explains how Telnxo supports applications.
Rules you must follow with a short code
Carriers audit short codes, and a programme that drifts from what was approved can be suspended. The usual obligations are these:
- Clear opt-in before any message, and records you can produce on request.
- STOP ends all messages immediately and HELP returns your name and contact details.
- Message frequency and cost disclosure, such as "Msg and data rates may apply".
- Sending only the approved content. A new use case needs a new application.
- Honouring quiet hours and local law on marketing consent, such as the
- Telephone Consumer Protection Act
- in the United States.
See our guide on opt-outs, sending windows and consent for practical wording.
Common mistakes with short codes
| Mistake | What happens | Better approach |
|---|---|---|
| Applying late | The launch date passes before the code is live | File weeks ahead and keep a bridge number ready |
| Vague opt-in wording | Application is rejected or the programme is suspended later | Show the exact words, the frequency and how to stop |
| Mixing purposes | Complaints on marketing damage alerts on the same code | Use separate codes or campaigns for separate purposes |
| Ignoring STOP | Complaints rise and carriers step in | Process opt-outs instantly and everywhere |
| No monitoring | Problems found only after blocking | Track delivery, complaints and opt-out rates weekly |
Keeping a short code programme healthy
Approval is only the start. Carriers watch complaint and opt-out rates for as long as the code is live, and a programme that drifts from what was approved can be paused. Treat the application as a promise: send the kinds of message you described, at the frequency you described, to people who agreed to receive them.
Clean your list regularly. Remove numbers that have unsubscribed, bounced or been disconnected, and use a lookup to find numbers that are no longer active before a large send. Segment by interest so people get messages they care about, and give them an easy way to change frequency rather than leaving altogether. Review your sample messages whenever you add a new type of content, and tell your provider before you change anything that might not match the approved description. A programme that is open with the carriers about changes keeps its code far more reliably than one that has to explain itself after a suspension.
A keyword flow in practice
User: JOIN
Brand: Telnxo: You are subscribed to order alerts, up to 4 msgs/month. Msg&data rates may apply. Reply HELP for help, STOP to cancel.
User: STOP
Brand: Telnxo: You are unsubscribed and will get no more messages.The welcome and stop replies are mandatory, and both are sent by your system the moment the keyword arrives. Our SMS platform handles keyword routing and sends incoming messages to your application by webhook.
Common questions about cost and planning
Plan the budget in three parts: the lease and set-up fees, the per-message cost, and the staff time to manage the programme. The first is predictable. The second depends on volume, so use the cost calculator to estimate. The third is easy to forget: someone must watch complaints, update the opt-in flow and keep records ready for an audit.
Timing is the other planning risk. Because activation can take weeks, a campaign built around a launch date needs the application filed well before it. If the date is close, a verified toll-free or registered local number can bridge the gap while the short code is provisioned. If you operate in several countries, compare the rules in each, because a short-code programme in one market does not carry over to another.
A short code buys speed and recognition. It is the right tool when volume demands it, and an expensive detour when it does not.
Not sure which number type you need? Tell us your volumes and countries and we will recommend the simplest route.
Frequently asked questions
What is a short code in SMS?
A short code is a special 5 or 6 digit phone number that businesses use to send and receive large volumes of text messages quickly. It is leased and approved by carriers rather than bought like an ordinary number.
How is a short code different from a long code?
A long code is an ordinary full-length phone number, which is slower and more lightly regulated. A short code is shorter, easier to remember, much faster and more heavily vetted.
How much does a short code cost?
Costs have several parts: a recurring lease for the code, one-off set-up and carrier fees and per-message charges. Amounts vary by country and change over time, so ask your provider for the current figures.
How long does it take to get a short code?
Provisioning commonly takes several weeks, because the application is reviewed and the code is activated on each carrier. Plan well before a launch date.
Can a short code receive replies?
Yes. Short codes are designed for two-way messaging, so people can reply with keywords such as JOIN, STOP or HELP and your system can respond automatically.
Do short codes work in India?
Commercial SMS in India mainly uses registered sender headers and templates under DLT rules rather than the short-code model used in the US. Check the rules for each country before planning.
Do I need a short code?
Most businesses do not. A registered local number or a verified toll-free number is enough for moderate volumes. A short code makes sense for very large campaigns, time-critical alerts or well-known keyword programmes.