.dockerignore Generator
Generate a .dockerignore from build-context presets so Docker sends less to the daemon on every build.
What is dockerignore Generator?
A .dockerignore generator. Docker copies the whole build context to the daemon before it can reuse a cache, so excluding node_modules, .git and build output is usually the largest single win in build time.
How it works
Preset blocks are merged and deduplicated exactly like the .gitignore generator, then linted with Docker's own rules in mind: patterns are evaluated from the build-context root, a leading ! re-includes, and a case that behaves differently from git (a negation inside an otherwise excluded directory) is reported as a warning rather than an error.
- Paste or fill in the input. Drop in a commit message, a diff, a package.json, a path list or a set of options. The tool reads it locally — nothing is uploaded and no repository is contacted.
- Adjust the rules to match your project. Every linter here takes its convention from a setting you can change: allowed commit types, header length, target branch length, known branch names. Set them once to what your team actually uses.
- Copy the result. Generated files copy straight to the clipboard or download as a real file with the right name (.gitignore, CODEOWNERS, LICENSE, COMMIT_EDITMSG), and Reset returns every field to its default.
Examples
A commit message that fails CI
"Updated(auth): Fixed the expired-token redirect." is rejected by release automation and reported here with the exact reasons: unknown type, capitalised description, past tense and a trailing period.
A .gitignore that only half works
The Checker shows which rule decides a path — and why `!keep.txt` inside an ignored directory never fires, the mistake that sends people to Stack Overflow.
A dependency bump nobody reviewed
The package.json Diff separates added, removed and changed entries per section, so a caret bump of a runtime dependency does not hide inside a lockfile-sized pull request.
A diff pasted from a code review comment
The Diff Viewer understands several `diff --git` blocks, mode-only changes, renames and binary stubs, and calls out a pasted `--stat` summary instead of rendering an empty box.
Common mistakes
Committing a .gitignore without checking it
Rules look right and behave differently: a pattern containing a slash is anchored to the root, a trailing slash means directories only, and a file inside an ignored directory cannot be re-included. Check the paths that matter before you commit the file.
Rewriting published history
A clean commit history is worth having, but amend, rebase and filter-repo change commit hashes. Only rewrite commits that nobody has pulled; after a rewrite, push with --force-with-lease rather than --force.
Treating a generated file as if it were reviewed
These tools produce a starting point, not a decision. Check the licence text against the canonical source, read the security policy before publishing it, and make sure a CODEOWNERS team actually exists — GitHub silently ignores rules whose owner has no write access.
Putting slow checks in a pre-commit hook
A hook that takes 30 seconds gets bypassed with --no-verify within a week, and then it protects nothing. Keep pre-commit to formatting and linting, move type checks and tests to pre-push or CI.
Frequently asked questions
How much difference does a .dockerignore actually make?
On a Node project the difference is usually the whole build time: without one, every build ships node_modules and .git to the daemon, which invalidates the COPY layer cache whenever anything in them changes.
Where should the file live?
Next to the Dockerfile you are building, or in the build-context root when that differs. Run docker build --progress=plain to see the context size it reports.
Is .dockerignore syntax the same as .gitignore?
Mostly. Docker supports the same wildcards, ** and a leading !, but trailing slashes and comment escaping behave slightly differently, so this tool keeps patterns simple enough to mean the same thing in both files.