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LLet's Encrypt
The nonprofit CA that made automated TLS the default — free, ACME-only, 90-day certificates.
Public CA (free)SaaS (ACME)By ISRGSince 2015Open source: Boulder (MPL-2.0)
- Type
- Public CA (free)
- How it works
- Issues domain-validated TLS certificates at no cost, exclusively through the ACME protocol. Short 90-day lifetimes force automation, which is the point: renewal is a cron job, not a calendar reminder.
- Deployment
- SaaS (ACME)
- Pricing*
- Free
- Free tier
- Yes
- Open source
- Boulder (MPL-2.0)
- Compliance
- WebTrust, CA/B Forum
- Best for
- Public web TLS on anything you can automate
- Notable
- Billions of certificates issued
* Indicative list pricing at August 2026 (vendor documentation and public pricing pages, August 2026), not a quote.
Strengths
- Free and genuinely unlimited in practice
- ACME everywhere — client support is universal
- Short lifetimes push good automation hygiene
- Run by a nonprofit with public transparency
Trade-offs
- Domain validation only — no OV or EV
- No support contract to escalate to
- Rate limits bite on very large estates
- No code-signing or S/MIME
Visit Let's Encrypt → Documentation
Listed for comparison as of August 2026 — not an endorsement, and Let's Encrypt did not pay for placement. See disclosure.
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