Most AI writing tools charge you every month whether you use them or not. Grammarly Premium runs $12–$30/month. That's up to $360 a year — even during the months you barely type anything longer than "on my way."
There's a simpler model: pay only for the AI you actually use.
The problem with AI writing subscriptions
Subscriptions make sense for tools you use at full intensity every day. But keyboard AI is bursty by nature:
- You need a grammar pass on an important email — then nothing for two days.
- You translate a handful of messages on a trip abroad.
- You polish one Upwork proposal a week.
Paying a flat monthly fee for bursty usage means you're subsidizing the heaviest users. Most people would spend far less on a metered plan.
How pay-as-you-go AI typing works
Synapse uses energy credits instead of a subscription:
- Download the keyboard free and sign up — you get 20,000 free credits to test everything.
- When you run low, top up starting at $5. No auto-renewal, no recurring charge.
- Credits are only spent when you actually invoke AI — fixing grammar, translating, or running a custom prompt. Regular typing costs nothing, ever.
Pay with a card or with USDT crypto, which adds a 1.3× energy bonus on top-ups.
What you still get without the monthly fee
No subscription doesn't mean fewer features. Inside any Android app — WhatsApp, Gmail, Instagram, Slack — Synapse gives you:
- One-tap grammar correction exactly where you're typing, no copy-paste round-trips.
- Translation to any language by writing a prompt like "translate to Portuguese, casual tone".
- Tone rewriting — turn a blunt draft into something professional (or the reverse).
- Custom AI prompts you define once and trigger with a tap, like reusable proposal templates.
Your typing data stays on your device; only the text you explicitly send to AI leaves your phone.
Subscription vs. pay-as-you-go: the math
| Grammarly Premium | Synapse | |
|---|---|---|
| Monthly cost | $12–$30 | $0 |
| Yearly commitment | up to $360 | Top-ups only when needed |
| Unused months | Still billed | Cost nothing |
| Custom AI prompts | No | Yes |
| Works in every Android app | Browser + limited apps | Yes, system-wide |
If you use AI assistance a few times a day, a single $5 top-up typically lasts weeks — a fraction of one month of a premium subscription.
Try it free
The best way to see if pay-as-you-go fits your usage is to test it with real messages. Download Synapse free — the 20,000 signup credits are enough to run grammar fixes, translations, and custom prompts for days without paying anything.