Proofly vs Letterhead
Side-by-side comparison of features, pricing, and ratings
At a glance
| Dimension | Proofly | Letterhead |
|---|---|---|
| Pricing | Free (open-source) | Contact for custom pricing |
| Target User | Individual writers, students, privacy-conscious users | Teams managing multiple newsletters (media companies, publishers) |
| Core Functionality | On-device grammar & spell check in Chrome | Newsletter production, audience management, revenue tools |
| AI Usage | Local Gemini Nano for error detection | Cloud AI agents for content curation and segmentation |
| Platform | Chrome extension only | Web-based platform, integrates with Zapier |
| Best For | Privacy-first writing assistance | Scaling email operations |
These tools address completely different needs. Proofly is a free, privacy-focused Chrome extension for on-device proofreading. Letterhead is a paid, enterprise-grade newsletter OS for teams managing multiple brands. Choose Proofly if you want a private, lightweight grammar checker; choose Letterhead if you run a multi-newsletter operation and need to scale production, audience management, and revenue.
Proofly is a free Chrome extension that proofreads your writing on-device with Chrome's built-in Gemini Nano AI — your text never leaves your machine.
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Letterhead is the newsletter portfolio platform that runs every title like a measurable product, on your ESP or as a full email OS.
Visit WebsiteWho should pick which
- Privacy-conscious studentPick: Proofly
Proofly runs completely on-device with no data transmission, is free, and works within Chrome for essay writing.
- Solo blogger using FirefoxPick: Proofly
Proofly only supports Chrome, so this user cannot use it. They should look for a cross-browser tool.
- Media company with 5 newslettersPick: Letterhead
Letterhead's portfolio management, AI agents, and revenue tools are designed for multi-newsletter operations.
- Enterprise needing email compliancePick: Letterhead
Letterhead offers governance, approval flows, and dedicated IP migration for enterprise deliverability.
- Open-source advocatePick: Proofly
Proofly is fully open-source, aligning with values of transparency and community-driven development.
Frequently Asked Questions
Proofly vs Letterhead: which should you choose?
These tools address completely different needs. Proofly is a free, privacy-focused Chrome extension for on-device proofreading. Letterhead is a paid, enterprise-grade newsletter OS for teams managing multiple brands. Choose Proofly if you want a private, lightweight grammar checker; choose Letterhead if you run a multi-newsletter operation and need to scale production, audience management, and revenue.
Does Proofly work in non-English languages?
The tool description focuses on English spelling and grammar, but Gemini Nano may support other languages depending on your Chrome version.
Can I use Proofly in Microsoft Edge?
No. Proofly only works in Chrome (version 141+). It is not supported on other Chromium browsers like Edge at this time.
Is Letterhead suitable for a single newsletter?
It's designed for multi-newsletter teams. For a single newsletter, simpler tools like Mailchimp might be more cost-effective.
Does Proofly require internet access?
After the initial model download, Proofly works offline. All processing is on-device.
What is the MCP server mentioned in Letterhead's news?
It's a native server that lets AI agents read data, sync audiences, and curate content across newsletters, announced in 2025.
Can I try Letterhead before purchasing?
It's contact-based pricing, likely with a demo. There's no self-serve free trial mentioned.
Does Proofly check style or tone?
No. It only corrects spelling, grammar, punctuation, and capitalization. It does not offer style suggestions.
Does Letterhead integrate with email service providers?
Yes. Its Studio mode layers on top of existing ESPs. Suite replaces the ESP. It also integrates with Zapier.
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Last reviewed: July 3, 2026