HCL

HCL. We trial it under Code in the garden.

Blurb

HCL is the HashiCorp configuration language. Contribute to hashicorp/hcl development by creating an account on GitHub.

Summary

HCL grew out of a practical constraint: when HashiCorp moved its tools to GoLang, embedding Go as an end-user DSL was awkward. They built a small declarative language tuned for blocks, attributes, and references. Those patterns 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.