lego

lego is a free, open-source ACME client and Go library for issuing and maintaining TLS certificates. It is best suited to developers and infrastructure operators who prefer command-line or embedded automation over a graphical certificate console. The broad provider and challenge support makes it adaptable, provided you are comfortable managing configuration and credentials yourself.

Overview

lego covers the core certificate lifecycle: obtaining, renewing, and revoking certificates, with support for wildcard and SAN certificates. Automatic renewal and deployment automation make it suitable for recurring production operations rather than one-off certificate requests. Revocation workflows add a practical control when a key or certificate must be withdrawn.

The project is independent, free, and released under the MIT license. There are no paid tiers or trial terms to weigh, so cost is not a barrier; the trade-off is that administration, integration, and support remain primarily the operator's responsibility.

Key features

Flexible ACME validation

DNS-01, HTTP-01, TLS-ALPN-01, and DNS-PERSIST-01 challenges cover substantially different network and DNS arrangements. DNS-01 enables wildcard issuance, while HTTP-01 and TLS-ALPN-01 can fit environments where DNS automation is undesirable. This choice is valuable for mixed infrastructure, but each method still requires correct domain, firewall, and provider configuration.

Multiple authorities and providers

lego works with multiple ACME servers, including Let’s Encrypt and ZeroSSL, so teams can select an authority that matches their policy or deployment. More than 200 DNS integrations include Cloudflare, Amazon Route 53, Google Cloud DNS, and Azure DNS. CNAME support is enabled by default, which helps when validation DNS is delegated. The breadth reduces the need for custom integration, although provider credentials and permissions must be maintained by your team.

Automation and integration

Use lego as a command-line client for scripts and scheduled jobs, or embed it as a Go library in a larger service. Credentials and provider settings are passed through environment variables, with values supportable from files or dotenv files. That approach fits containers and CI pipelines, but it puts secret storage, rotation, and accidental exposure firmly in the deployment design.

Standards and distribution

The project lists support for ACME RFC 8555 and several certificate validation and renewal extensions. Prebuilt binaries cover operating systems and architectures, and a Docker image is provided. Installation instructions also cover package managers and source builds. Maintainers maintain the AUR and Snap packages; other package listings are community maintained, so update cadence can differ by channel. Building from source requires Go 1.25 or later.

Pricing

There is no free trial because the software is permanently free, and no published seat, quota, or renewal fee. This is the right fit for individuals, teams, and service operators that can run and maintain their own automation. Organizations wanting vendor-managed administration or commercial support should assess a different category of product.

Platforms

lego is available for API use, Linux, macOS, and self-hosted deployments. Binaries, Docker, package-manager instructions, and source installation give infrastructure teams several distribution routes. It is not presented as a hosted web application, so operation remains tied to your own environment.

Who it's for

Choose lego when certificate issuance must be scripted, embedded in Go software, or repeated across providers and environments. It is especially well matched to platform teams managing wildcard or SAN certificates and to deployments that need DNS-based validation across many registrars. It is less suitable for administrators who expect a graphical dashboard, centralized hosted controls, or a vendor to handle credential and package upkeep.

Pros and cons

Pros

• Broad validation coverage: four challenge methods accommodate varied DNS, HTTP, and TLS topologies.
• Large DNS ecosystem: more than 200 providers, including major cloud DNS services, reduce custom integration work.
• Complete lifecycle automation: issuance, renewal, deployment, and revocation support ongoing operations.
• CLI and Go library: the same project serves shell automation and native Go integrations.
• Flexible distribution: binaries, Docker, packages, and source builds fit self-hosted environments.

Cons

• Credential ownership stays with you: environment-variable configuration is flexible but requires disciplined secret handling.
• Source builds have a current toolchain requirement: Go 1.25 or later may be inconvenient on older build systems.
• Package support varies: only AUR and Snap packages are maintained by the project; other packages depend on their communities.
• No graphical management layer is presented: teams seeking visual policy and certificate administration should look elsewhere.

Alternatives

Certify The Web is a better direction if you want a freemium option with a no-limit free evaluation and broader web and Windows platform coverage.

acme.sh is the leaner choice when a free, shell-script ACME client on Linux, macOS, self-hosted systems, or Windows is preferable.

Certbot is another free, open-source ACME client for users who prefer the Electronic Frontier Foundation-backed project.

EJBCA fits teams seeking a broader open-source PKI platform with a community edition aimed at learning, testing, and prototyping.

Let's Encrypt is the direct choice when you need a free certificate authority rather than an ACME client.

OpenXPKI suits organizations wanting a fully functional open-source PKI code base with Debian packages and documentation.

GeoTrust is the commercial alternative for paid SSL services and monitoring.

Qualys External Attack Surface Management is aimed at broader external-asset security management rather than certificate automation alone.

Browse more tools in Certificate Management Software.

Verdict

lego is a strong recommendation for technically capable operators who need free, scriptable certificate lifecycle management with many challenge methods, authorities, and DNS providers. Its MIT-licensed CLI and Go library keep deployment flexible and cost-free. Look elsewhere if your priority is a hosted dashboard, turnkey credential management, or vendor-managed support rather than self-hosted automation.