Free tool
Spintax validator and previewer
Paste a subject line or an email with spintax.
Free guide19 min read
Send 100,000 cold emails a month
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About this tool
About the spintax validator
The validator reports unbalanced braces, empty options, spaces at option edges that get trimmed at send time, nested spintax, fallbacks inside spintax and nested fallbacks, then renders samples with filled and with empty merge fields.
It reads both formats: double-brace {{RANDOM|a|b}} (Instantly and tools that copy it) and single-brace {a|b} (most other sequencers).
How it works
The errors that reach real inboxes
- Spaces at the edge of an option: engines that trim options join words, so {{RANDOM|quick| short}} note becomes shortnote
- Nested fallbacks: {{firstName|{{companyName|there}}}} usually ships the inner tag raw when the first name is empty
- A fallback pipe inside single-brace spintax: in {Hi {{first_name|there}}|Hello} the fallback's | splits the block
- Variables that are not columns in your lead file: they render as an empty string, so the email says "Hi ,"
Background
How to read the renders
Filled renders use sample values for every variable. Empty renders leave every variable blank, which is what a lead with missing data gets. Both must read like an email a person wrote.
The render count is the number of distinct texts the template can produce, excluding variable values. At high volume, subject lines need a large count; every render still has to make sense.
Cold email subject lines covers how to write the subject lines you vary here.
The spintax linter skill runs the same checks in Claude or ChatGPT on a whole sequence and proposes a fixed template.
Questions
What is spintax in cold email?
Spintax is a template syntax that picks one option from a list for each email, such as {Hi|Hello}. It makes emails sent at volume differ from each other.
Why does my spintax show raw braces in sent emails?
Usually a brace is not closed, the tool uses a different syntax ({a|b} versus {{RANDOM|a|b}}), or a fallback is nested inside another tag. Paste the template here to find which.
Does spintax stop emails from going to spam?
Not on its own. It prevents identical emails at volume. Placement depends mostly on the sending domains and mailboxes, the list and the content itself.
Is my text sent anywhere?
No. The validator runs in your browser.
In your AI assistant
Run the same checks in Claude or ChatGPT
Free SKILL.md files with the rules behind this tool. Install them in Claude or Claude Code, or paste them into ChatGPT, Gemini, Grok or Cursor.
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Deliverability call
Talk to our deliverability team
Book a call with the people who run our mailbox infrastructure. We look at your current setup and tell you what to change.
- Review your domains, DNS records and current inbox placement
- Size the setup: domains, mailboxes per domain and daily volume per mailbox
- Plan warmup and the move from your current provider or sequencer
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