Heroku Labs: Build Time Config Vars
Last updated July 17, 2025
This Heroku Labs feature is only applicable to apps that use Cloud Native Buildpacks.
By default, an application’s config vars are only available during runtime for Fir-generation apps. To make variables available during both build time and runtime, you can enable the Build Time Config Vars Heroku Labs feature, in the application’s project.toml:
[com.heroku.build.labs]
build_config_vars = true
To disable the feature, set build_config_vars to false in the file, or remove it from the file entirely.