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Unsupported YAML Function Validation

· 2 min read
Erik Osterman
Erik Osterman
Founder @ Cloud Posse

Atmos now detects unsupported and misspelled YAML function tags before configuration processing continues. Invalid tags return a clear error with the supported Atmos YAML functions, so typos fail fast instead of being silently treated as ordinary YAML.

What Changed​

Atmos validates explicit custom YAML tags during atmos.yaml and stack manifest processing. If a tag is not one of the supported Atmos YAML functions, Atmos returns an unsupported tag error that includes the valid options.

vars:
  home: !envv HOME

Instead of quietly accepting the misspelled !envv tag, Atmos reports that the tag is unsupported and points users toward valid functions like !env, !exec, !include, and the other supported YAML tags.

Exact Matching​

Validation uses exact tag matching. A misspelled function such as !envv no longer matches the supported !env prefix, which prevents typos from slipping through parser or resolver paths that previously checked only the beginning of a tag.

Standard YAML tags such as !!str continue to work normally.

Why It Matters​

YAML functions are often used for dynamic values: environment variables, Terraform outputs, secrets, Git metadata, and included files. A misspelled tag can otherwise hide until much later in a deployment workflow, where the failure is harder to connect to the original configuration.

Failing at parse or processing time makes the error immediate and actionable.

Get Started​

No configuration is required. Use the documented Atmos YAML functions as usual, and Atmos will report unsupported tags when it finds them.