Dockle

Dockle is a self-hosted command-line linter for container images, focused on security findings and Docker best practices. It suits developers and platform teams that want checks inside local builds or continuous-integration pipelines rather than a hosted security service. Its strongest case is configurable, standards-aware image review with automation-friendly output; teams wanting a managed interface will need another approach.

Overview

Dockle examines container images for vulnerabilities and configuration problems that can undermine a production image. Its checkpoints include the CIS Docker Image Benchmarks, along with Docker- and Linux-specific settings such as empty passwords and duplicate user or group IDs. That combination makes it useful both as a vulnerability gate and as a practical review of image construction choices.

The project is open source under the Apache-2.0 license and uses a self-hosted deployment model. You install and operate it wherever your build or review process runs, so it avoids a hosted subscription but leaves maintenance and integration work to your team.

Key features

Security and best-practice checkpoints

CIS-aligned checks give security-conscious teams a recognizable baseline, while Docker- and Linux-specific rules catch issues that a generic vulnerability scan may not address. Empty-password and duplicate-UID or group checks are especially relevant to images moving from development into shared or production environments.

Automation and reporting

Dockle can print or save results as JSON and SARIF. JSON works for scripts and internal tooling; SARIF is suited to systems that ingest static-analysis findings. Configurable exit levels let a team decide which findings fail a build, and selected checkpoints can be ignored through command options, environment variables, or a .dockleignore file. Those controls help introduce the linter gradually, but they also require discipline so exceptions do not quietly weaken the gate.

CI and registry coverage

Documented CI usage includes a GitHub Action and examples for Travis CI, CircleCI, and GitLab CI. Dockle also documents private-image access for Docker Hub, Amazon ECR, Google Container Registry, and self-hosted registries. Private registry credentials are configured with environment variables; the project advises against putting those credentials on a local machine, which makes secure CI configuration the more appropriate pattern.

Image inputs

Alongside registry-based images, Dockle can scan an archive produced by docker save with its --input option. This is useful when an image must be reviewed from a file rather than pulled from a registry.

Pricing

There is one free plan, with no paid tier, seat charge, quota, or trial term stated. It is a good fit for individuals and teams that can run open-source tooling themselves. The trade-off is operational: the plan provides the software, not a hosted service or a vendor-managed deployment.

Platforms

Dockle supports Linux, macOS, and Windows. Installation routes include Homebrew, RHEL/CentOS, Debian/Ubuntu, Arch Linux, Windows binaries, version managers, source builds, and Docker. That breadth suits mixed developer workstations and CI environments, while the number of installation choices means teams should standardize one supported route for repeatable builds.

Who it's for

Choose Dockle if your team builds Docker images and wants CIS-informed checks, Docker and Linux configuration rules, adjustable failure thresholds, and machine-readable findings in local or CI workflows. It is particularly appropriate for teams comfortable managing a self-hosted command-line tool and handling registry credentials in CI.

Look elsewhere if you need a hosted console, centralized administration, or a service that reduces installation and operational responsibility. Dockle is an image-focused linter, not a broad managed security platform.

Pros and cons

Pros

• Free and Apache-2.0 licensed: teams can adopt the linter without a subscription cost.
• Standards plus practical rules: CIS benchmarks are complemented by Docker- and Linux-specific checks, including empty passwords and duplicate IDs.
• CI-ready output: JSON, SARIF, a GitHub Action, and examples for several CI systems support automated gates and reporting.
• Flexible image access: it covers major private registries and saved image archives as well as ordinary image workflows.

Cons

• Self-hosted operation: installation, upgrades, runtime, and credential handling remain your team's responsibility.
• Exception management needs care: exit-level changes and ignored checkpoints can make enforcement less meaningful if they are not governed.
• Image-linter scope: teams seeking a hosted, wider security-management experience will need another product.

Alternatives

• Docker Desktop is the better choice when you want a freemium desktop environment spanning Docker Engine, Kubernetes, Docker Hub, Docker Scout, and Docker Debug; its Personal plan is free and Pro is $9 a month.
• Snyk Open Source suits teams wanting a freemium service with API and web access; its free plan covers five projects and Team costs $25 a month.
• Kubescape is an alternative for Kubernetes-focused work, offering a free Apache 2.0 CLI and operator in a self-hosted model.
• Trivy is a free Apache-2.0 open-source scanner for teams that want a different vulnerability-scanning tool.
• Deepfence ThreatMapper is a free option with no limits or hidden features for teams seeking broader deployment choices.
• Grype is a free Apache-2.0 licensed open-source vulnerability scanner.
• Kyverno is a free Apache License 2.0 open-source project for teams evaluating policy-oriented tooling.
• Qualys External Attack Surface Management is the alternative when a freemium, web- and API-based service with a 30-day free trial is preferable.

See the broader Container Security Software category for more options.

Verdict

Dockle is a strong choice for developers and platform teams that want a free, self-hosted Docker image linter with CIS benchmarks, configurable enforcement, and CI-friendly reports. Choose it for focused image quality and security gates; look elsewhere when you need a managed console or security coverage beyond the image itself.