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Keep version fields in JSON files in sync without a template

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

Plain JSON has no comment syntax, so there's nowhere to put an annotation telling a tool which field carries a managed version. Rewriting the whole file from a parsed structure works, but it reflows formatting, reorders keys, and turns a one-line diff into a noisy one. Neither option was a good fit for keeping a version field in a package.json, plugin manifest, or marketplace listing in sync with a locked dependency.

The Problem​

The Version Tracker's marker manager rewrites version tokens on lines annotated with an atmos:version comment — but JSON has no comment syntax, so there's no line to annotate. The template manager covers formats like this by rendering a *.tmpl source to a sibling output file, but that means maintaining a template and a generated file as two files that have to be kept in sync by hand every time an unrelated field in the JSON document changes.

The Fix​

A new json file manager writes locked values directly into JSON files at configured field paths. It patches only the targeted field and leaves everything else in the document — key order, spacing, unrelated fields — exactly as it was, so atmos version track apply produces a minimal, single-field diff instead of a fully reformatted file.

How to Use It​

version:
  dependencies:
    atmos:
      ecosystem: github/actions
      datasource: github-releases
      provider: github
      package: cloudposse/atmos
      desired: "~1.160"

  files:
    - manager: json
      paths:
        - package.json
      options:
        set:
          - path: version
            from: atmos

A single rule can target more than one file, and a single file can carry more than one managed field — each just needs its own path/from entry under set:

  files:
    - manager: json
      paths:
        - package.json
      options:
        set:
          - path: version
            from: cli
          - path: engines.node
            from: node

atmos version track apply rewrites every configured field from the lock; --check fails and lists any file that's out of date, so CI can catch drift before it merges.

Get Involved​

See the Version Files docs for the full path/from syntax, including array indexing and escaping keys that contain literal dots. Have feedback on this feature? Open an issue or join the conversation in the Cloud Posse community Slack.