Heroku Labs: Build Time Config Vars
Last updated March 13, 2025
This Heroku Labs feature is only applicable to Fir-generation apps.
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.