A promotional text gets read inside 90 seconds, and a sloppy one gets reported almost as fast. SMS click-through runs well ahead of email — Omnisend’s 2026 benchmarks put campaign SMS around 12% CTR and triggered/automated SMS above 20% — but a single non-compliant blast can trigger TCPA fines that start at $500 per message and reach $1,500 per willful violation, plus carrier filtering that throttles your whole number. These prompts force the four things a promo text actually needs: one 160-character GSM-7 segment, a named sender, a STOP that is not buried, and an offer worth interrupting someone for. Pair them with email marketing prompts for the longer companion send.
TL;DR
- Keep every promo to one segment: 160 chars in plain GSM-7, or 70 chars the moment you add an emoji or accented character (Unicode/UCS-2 drops the limit). Aim for 100-130 chars for the best read rate.
- TCPA requires documented prior consent, a working opt-out (STOP, plus any reasonable wording since the April 2025 rule), and removal within 10 business days of revocation.
- Honor quiet hours: 8am-9pm recipient local time federally; stricter in FL/OK/WA (8am-8pm) and TX (9am-9pm).
- Any current model handles SMS copy. Use GPT-5.5 or Claude Sonnet 4.6 for tone variants; lean on the character-count discipline in the prompt rather than trusting the model to count.
Which AI to use for SMS copy
All of these prompts work in any chat model, but the practical differences as of June 2026:
| Model | Plan / price | Why for SMS | Watch out |
|---|---|---|---|
| GPT-5.5 (Instant) | ChatGPT Free / Plus $20 | Fast, punchy variants; good at brand-voice matching | Will quietly exceed 160 chars — always make it print the count |
| Claude Sonnet 4.6 | Claude Free / Pro $20 | Strong at restraint (no fake urgency, no all-caps) | Same: verify the character count yourself |
| Gemini 3.1 Pro | Google AI Pro $19.99 | Good when pulling offer data from a Workspace doc | Tends toward longer, “marketing-speak” first drafts |
Models cannot reliably count characters, so the count requirement lives in the prompt and you confirm it in a counter before sending. See chatgpt-compare-models if you are choosing a plan.
Best for
- DTC store promos
- Restaurant / local-business promos
- App push-substitute SMS
- Subscription renewal nudges
- Event reminders
1. Standard promo SMS (160 chars)
Write 5 promotional SMS variants for [offer]. Hard limit 160 GSM-7 characters each (no emoji, no accents). Print the character count after each. Include: brand name, the offer in one line, a short-URL placeholder, and "Reply STOP to opt out". Write for someone who opted in for sale alerts.2. Time-sensitive flash sale
Write 3 flash-sale SMS variants for [offer] ending in [hours] hours. Max 160 GSM-7 chars; print the count. Lead with the deadline. No "URGENT", no all caps. Include short-URL placeholder + STOP. Use only real urgency.3. Restock / back-in-stock SMS
Write 3 restock SMS variants for [product] the customer waitlisted. Max 160 GSM-7 chars; print the count. Name the product specifically (not "your item is back"). Add one line on limited stock only if true. Include STOP.4. Cart-abandon SMS
Write 3 cart-abandon SMS variants, max 140 chars (leaves room for first name). Soft tone — they shopped about an hour ago. Use [first_name] if available, refer to the item generally, short-URL placeholder, STOP. Print the count.5. Subscription-renewal nudge
Write 2 renewal-nudge SMS variants to send one week before renewal. Max 160 GSM-7 chars; print the count. State the price, the renewal date, and how to cancel. Compliance-friendly. No scarcity tricks.6. App-install / re-engagement SMS
Write 3 SMS variants nudging dormant app users (60+ days inactive) back. Max 160 GSM-7 chars; print the count. Name one specific new feature, include a deep-link placeholder, and STOP.7. Loyalty-tier reward SMS
Write 3 SMS variants telling a customer they reached a new loyalty tier. Max 160 GSM-7 chars; print the count. Give the concrete benefit, how to redeem, and STOP. Friendly, no marketing speak.8. Event / appointment reminder
Write 2 reminder SMS for [event_or_appointment] in [hours] hours. Max 160 GSM-7 chars; print the count. Include date/time, location or link, a reschedule path, and STOP. Useful, not promotional.9. Holiday promo without sounding corporate
Write 3 holiday SMS for [holiday]. Max 160 GSM-7 chars; print the count. No generic "Happy [holiday]!" filler — lead with the actual offer. Match this brand voice: [describe voice].10. New-customer welcome SMS
Write 3 welcome SMS variants for a customer who just opted in to SMS. Max 160 GSM-7 chars; print the count. Confirm the subscription, restate the value (e.g. 10% off first order), how to redeem, and STOP. This is the first message — set expectations on message frequency.11. SMS A/B test plan
Build an A/B test plan for promo SMS. Variables to isolate: lead-with-offer vs lead-with-deadline; emoji vs no emoji; first-name vs generic. Produce 6 variants paired into 3 isolated tests, each with a one-line hypothesis and the metric to read (CTR or conversion).12. SMS deliverability + compliance audit
Audit the SMS below for deliverability and TCPA/CTIA compliance:
(a) all-caps or known spam-trigger words,
(b) sender/brand identified,
(c) opt-out instruction present and not buried,
(d) link uses a branded short URL (public shorteners like bit.ly are often carrier-filtered),
(e) GSM-7 character count and whether any character forces UCS-2 (70-char limit).
Flag each issue and rewrite to fix it.
[paste SMS]Character budget that actually matters
The single most common reason a “perfect” SMS costs double or gets cut is encoding. Build this into your sending checklist.
| Encoding | Single message | Per segment (concatenated) | Triggered by |
|---|---|---|---|
| GSM-7 (plain text) | 160 chars | 153 chars | Standard Latin text |
| UCS-2 (Unicode) | 70 chars | 67 chars | One emoji, an em-dash, curly quotes, or any accented/non-Latin character |
One stray emoji or a smart-quote pasted from a doc silently flips the whole message to UCS-2 and turns your 158-character “single” SMS into two billed segments. Keep promos in plain GSM-7 and verify the count in a calculator before sending.
Common mistakes
- All caps and “URGENT” — carriers and people both filter you out.
- No sender identification — looks like phishing and gets reported.
- Opt-out missing or buried in a second segment. STOP must be in the message, and since April 2025 you must also honor any reasonable opt-out wording (cancel, end, unsubscribe, quit).
- Going over one segment — split messages confuse readers and double your cost; an unnoticed emoji does this via UCS-2.
- Blasting the same promo to subscribed and unsubscribed segments — breaks trust and risks TCPA ($500-$1,500/message) or GDPR exposure for EU contacts.
- Sending outside quiet hours — 8am-9pm recipient local time federally, tighter in several states.
- Faking scarcity (“only 3 left!” when there are not) — one screenshot circulates and the brand pays for it.
FAQ
How many characters can one promotional SMS be? 160 in standard GSM-7 encoding. The instant you add an emoji, em-dash, curly quote, or accented letter, the message switches to UCS-2 and the limit drops to 70 characters per segment. The 2026 sweet spot for read-through is 100-130 characters.
Can the AI count characters for me? Not reliably — language models estimate token-ish lengths and routinely miss the 160 mark. Keep “print the character count” in every prompt as a forcing function, then confirm in a real SMS character counter before you schedule the send.
What does TCPA require for a promo text in 2026? Documented prior express consent (a purchase alone is not consent), a clear opt-out you honor within 10 business days, and respect for quiet hours (8am-9pm recipient local time federally). The FCC’s “one-to-one consent” rule was vacated in 2025, but the revocation and opt-out rules are in force.
What are good benchmarks for a promo SMS campaign? Per Omnisend’s 2026 data, a one-off promo campaign averages around 12% click-through, while triggered/automated SMS (cart, welcome, restock) clears 20% and converts far better than a broadcast blast. Holiday-season campaigns push CTR above 20%. Keep per-send opt-out below ~0.5%; if it climbs past 1.5% on a single send, your frequency or targeting is off.
Should I include a link, and which shortener? Yes, but use a branded short URL from your SMS platform. Public shorteners like bit.ly are frequently flagged by US carrier filters and can silently kill delivery.
Related
- Email marketing prompts
- Abandoned cart email prompts
- CTA prompts
- Marketplace listing title prompts
- Landing page section prompts
Tags: #Prompt #E-commerce #E-commerce