Short Links in SMS

SMS is 160 characters. Every character the link uses is a character the message cannot. Short links are not optional in SMS campaigns — they are a functional requirement.

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SMS Link Fundamentals

A standard SMS message segment is 160 characters (GSM-7 encoding) or 70 characters (Unicode, required for emoji, non-Latin scripts and some special characters). When a message exceeds one segment, it splits into multiple concatenated segments — each billed separately by most SMS providers.

A full destination URL with UTM parameters — the tracking information necessary for GA4 attribution — can easily consume 150+ characters:

SMS Link Analytics: No Referrer by Design

Clicks on SMS links produce no HTTP Referer header. When a recipient taps a link in an SMS message, their device opens it in the browser without transmitting any referrer information. The click arrives at the destination (after the short link redirect) with a blank referrer — classified as direct traffic in GA4.

This is not a bug or a privacy setting — it is the inherent behaviour of SMS as a channel. SMS messages are not web pages; they have no referrer concept. Every SMS-driven click appears as direct traffic in GA4 without UTM parameters.

Solution: UTM parameters on the short link's destination URL. Use utm_source to identify the specific SMS send and utm_medium=sms to categorise the channel:

The short link hides these parameters from the visible SMS message; GA4 receives them on arrival at the destination.

Carrier-Level Link Filtering

Mobile carrier networks in many markets apply automated filtering to SMS messages — screening for spam signals including:

• Known spam domains. URLs on domains that have been used in SMS spam campaigns are flagged. Generic shared shortener domains with poor histories may be blocklisted at carrier level — meaning messages containing those domains are filtered before delivery regardless of the message content.
• Content patterns. Message templates matching known phishing or spam patterns are flagged independently of link domains.
• Sender behaviour. High-volume sends from unregistered sender IDs, sudden traffic spikes and other behavioural anomalies trigger carrier filtering.

Branded custom domains with a clean sending history are significantly less likely to trigger carrier link filters than generic shared shortener domains. The domain reputation case for branded links is stronger in SMS than in almost any other channel — because carrier filtering operates at the domain level and has no equivalent of "content quality" to balance against domain reputation.

India: TRAI Compliance and 2s.ms

India's TRAI DLT framework adds regulatory-level URL whitelisting on top of carrier filtering. Only URLs whose static portion (https://domain.tld/HEADER/) has been registered and approved on the DLT platform are permitted in commercial SMS to Indian mobile numbers. See TRAI SMS Compliance and DLT Header for the full regulatory framework.

Cuttly's 2s.ms domain is a 5-character domain designed for TRAI-compliant Indian SMS — the shortest possible domain to conserve SMS character budget. A 2s.ms link uses only 5 characters for the domain, versus 12–20+ for typical branded domains, directly reducing multi-part message costs at scale.

SMS Link Best Practices

• Always use a short link. Full URLs in SMS are not viable for any campaign of meaningful content — they consume the entire character budget.
• Always use UTM parameters on the destination URL. SMS traffic is invisible in GA4 without UTM tags.
• Use a branded domain. Carrier filter risk and recipient trust both favour branded over generic shortener domains.
• Check message length before sending. Count the final character length including the link — ensure the message stays within one segment (or budget for multi-part costs deliberately).
• Test link delivery before campaign sends. Send a test message to real devices on the target carrier networks and verify the link delivers and resolves correctly before mass sending.
• For India: ensure DLT compliance before any commercial SMS. Non-compliant messages are blocked at carrier level before delivery.

Related Terms

• Short Links in WhatsApp
• TRAI SMS Compliance
• DLT Header
• UTM Parameters
• Benchmark Click Rates