HCL
HashiCorp Configuration Language (HCL) is a human-readable DSL for structured configuration. It is the native language of Terraform, and also used by Packer, Nomad, Vault, and historically Vagrant. HCL predates YAML’s dominance in Declarative IaC and remains the right choice when you are committed to the Terraform or OpenTofu toolchain—not as a general-purpose alternative to YAML for Kubernetes manifests or Docker Compose.
Rated trial: still the practical default inside HashiCorp-style IaC, but the 2023 BSL license change and growth of YAML-first and CDK-style tools (Pulumi) mean you should confirm ecosystem fit before new platform bets, not adopt HCL in isolation.
Blurb
HCL (HashiCorp Configuration Language) is a configuration language built by HashiCorp. HCL is designed to be both human- and machine-friendly, for use with command-line tools, but specifically targeted towards DevOps tools, servers, and configuration files.
Summary
HCL grew out of a practical constraint: when HashiCorp moved its tools to GoLang, embedding Go as an end-user DSL was awkward, so they built a small declarative language tuned for blocks, attributes, and references—patterns that map cleanly to infrastructure resources. It is intentionally not Turing-complete in the same way as a general programming language; expressions and functions exist, but the model stays declarative, which keeps diffs reviewable and state plans predictable.
For greenfield work outside Terraform/OpenTofu, YAML (plus optional templating via Helm or YAMLScript) or imperative/semantic IaC via Pulumi often wins on hiring surface area and license clarity. Inside an existing Terraform or OpenTofu estate, learning HCL is non-optional.
Details
- Syntax families: Native HCL (
.tf,.hcl), JSON syntax as an alternate encoding for the same Terraform schema, and HCL2 as the current generation used by modern Terraform. - Ecosystem: Tied to Terraform; OpenTofu maintains compatible HCL. Other HashiCorp products consume HCL-shaped config but are separate adoption decisions.
- License context: HashiCorp’s BSL shift does not change HCL’s technical role but affects how aggressively to standardize on HashiCorp-only stacks versus forks or YAML-native tools.
- When to prefer alternatives: Kubernetes and cloud-native config (YAML), cross-cloud app-centric IaC (Pulumi), or policy expressions embedded in APIs (CEL) rather than full resource graphs.