smler.in HEADER Format: The 30-Character TRAI Compliance Breakdown

smler.in is a purpose-built domain for one job: fitting a TRAI-compliant HEADER into an SMS link without blowing past the 30-character limit telecom operators enforce. If you want the full picture of TRAI SMS compliance, including custom domains and header setup, read our complete guide to TRAI compliance with Smler.in. This page focuses on the character math and the specific restrictions you'll run into.

What is smler.in used for?

smler.in is a short domain reserved specifically for SMS marketing links that need to carry a TRAI-mandated HEADER. Unlike a general-purpose shortener, its whole design is built around leaving as much room as possible for your HEADER and dynamic link ID, so the final URL still clears India's 30-character SMS link limit.

How many characters does the HEADER format actually use?

The math is fixed once you know the pieces. smler.in's domain, including "https://", takes 14 characters. Add a 7-character HEADER (the sender identifier TRAI requires) and you're at 21 characters, leaving 9 characters for the dynamic part of your short link.

A link in this format looks like:

https://smler.in/HEADER/{dynamicShortLinkID}

That structure keeps you inside the limit while still leaving a usable ID length, which is more headroom than many longer domains can offer.

Is smler.in a general url shortener or an SMS-specific tool?

smler.in serves as a versatile tool for a variety of needs. While it is built to handle compliance-first requirements for SMS campaigns, it also functions as a general URL shortener. It is suitable for a wide range of use cases, including social media bios, blog site redirection, offers, and marketing campaigns.

What other alternatives exist if I want my own branded HEADER domain?

The main alternative to using smler.in directly is bringing your own custom domain and adding HEADER support to it. That gives you the same compliance benefit with your own branding, for example:

https://yourbrnd.link/HEADER/{dynamicShortLinkID}

Setting this up follows the same domain and header configuration steps covered in our custom brand domains guide. If your SMS links also need to route users to a specific landing experience from the root domain, see our root routing guide.

Does the tool restrict which headers or characters I can use?

Yes, in one specific way: the HEADER itself has to be the sender identifier registered with your telecom operator under India's DLT (Distributed Ledger Technology) framework, not an arbitrary string you invent. smler.in doesn't restrict what you can shorten, but it does assume the HEADER you add is the one your operator has on file, since that's what actually clears the message for delivery.

What does the TRAI/DLT header actually do in an SMS link?

The HEADER ties a shortened link back to a specific registered sender or campaign. TRAI requires this so telecom operators can verify where a promotional SMS is coming from. Without a valid HEADER in the URL, operators can and do block the message outright, which means the campaign never reaches the recipient regardless of how good the offer is.

How do I start using smler.in for an SMS campaign?

Register your account, connect the HEADER assigned to your sender ID, and generate links in the HEADER/{dynamicShortLinkID} format shown above. From there you get the same tracking and analytics available across Smler, including click and delivery data on every link you send. Pricing for the service is listed here: smler.in pricing.

FAQ

What is smler.in?
smler.in is a short domain built specifically for SMS marketing links that need a TRAI HEADER. Its 14-character domain length is designed to leave maximum room for the HEADER and dynamic link ID while staying under India's 30-character SMS link limit.

Are there other alternatives to smler.in for compliant SMS links?
Yes. You can use your own custom domain with HEADER support instead of smler.in directly, keeping your branding while meeting the same TRAI requirement. The setup steps are the same as configuring any custom domain on the platform.

Is smler.in a general url shortener?
No. It's a narrow, compliance-focused domain for SMS campaigns that require a HEADER. For general shortening needs outside SMS compliance, a standard branded short domain is a better fit.

Does the tool restrict which characters or headers I can use?
The main restriction is that your HEADER must match the sender ID registered with your telecom operator under the DLT framework. Outside of that, the tool doesn't limit what content you shorten, only how the HEADER portion of the URL is formatted.

What does the SMS/TRAI header do?
It identifies the registered sender behind a promotional SMS. Telecom operators check for a valid HEADER before delivering the message, and links without one risk being blocked entirely, so including it correctly is what keeps campaigns landing in inboxes.