Python, Ruby, or Go runtime version mismatch

April 30, 2026 · View on GitHub

Playbook ID: runtime-mismatch Category: build Severity: high Tags: node, python, ruby, go, java, version

What this failure means

The installed Python, Ruby, or Go runtime does not satisfy the version constraint declared by the project. The build is using a language runtime outside the version range expected by the repository or dependency set.

Common log signals

requires python
requires ruby version
unsupported python
go.mod requires go
go version .* required
python.*requires.*version
incompatible python version
requires Python >=

Diagnosis

The installed Python, Ruby, or Go runtime does not satisfy the version constraint declared by the project. This playbook is the generic fallback for those runtimes after more specific Node.js and Java rules have been considered.

Fix steps

  1. Identify the required version from the repository source of truth: .python-version, .ruby-version, .tool-versions, go.mod, or the CI image tag.
  2. Pin the same version in the workflow or container image that runs the failing job.
  3. Re-run the build locally with the pinned runtime so you can confirm the version mismatch is resolved before re-running CI.
  4. If the failure came from a dependency upgrade, confirm the new minimum runtime requirement before relaxing project constraints or changing the CI image.

Validation

  • Print the runtime version in CI and confirm it matches the version file or toolchain declaration.
  • Re-run the failing workflow step and confirm the original version error is gone.

Likely files to inspect

  • .python-version
  • .ruby-version
  • .tool-versions
  • go.mod
  • .github/workflows/*.yml
  • .github/workflows/*.yaml

Run Faultline

faultline analyze build.log
faultline explain runtime-mismatch
faultline workflow build.log --json --mode agent

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Generated from playbooks/bundled/log/build/runtime-mismatch.yaml. Do not edit directly — run make docs-generate.