Automatically updating dependencies with dependabot


Outdated packages can open your application up to security issues. Moreover, newer versions will often have performance improvements, bug fixes and generally fewer problems. Keeping them up to date over multiple codebases can be quite painful, but it's possible to bring this effort down to close to zero with a bit of up-front effort.

This post applies only if you're hosting your code on GitHub. If not, there are managed options for dependency upgrades, such as Snyk. It's very expensive, but does a lot of other things too. If you are on GitHub, this is a free or cheap alternative.

First, a few pre-requisites. You'll need to ensure "Allow auto-merge" is enabled in your repository settings. You should also configure dependabot security alerts in the "Security" tab. These alerts happen outside of the dependabot schedule we'll set up later, and will ensure you get critical security updates as quickly as possible. You'll also need to make sure GitHub Actions is enabled for your repository.

Next, you'll need to create a new file for the dependabot configuration:


version: 2
  - package-ecosystem: "github-actions"
      - "<your_github_username>"
    directory: "/"
      - "<your_github_username>"
      day: "monday"
      interval: "weekly"
      time: "09:00"
      timezone: "Europe/Amsterdam"
  - package-ecosystem: "pip"
      - dependency-type: all
      - "<your_github_username>"
    directory: "/"
      - "<your_github_username>"
      interval: "daily"
      time: "09:00"
      timezone: "Europe/Amsterdam"

The confiration is quite straightforward. Note there are two package-ecosystem sections defined. One of these is for pip, which will also work for pipenv and poetry. The other will keep any GitHub actions you use up to date. We'll be using one of these soon, so it seemed good to add it. You can set the schedule however makes sense for your workflow. You don't need to set assignees and reviewers, but I like to add them so they show up in my GitHub notifications and I can make sure I don't miss anything. Not every update will be able to be merged automatically, so it's good to know about them.

One other important thing here is the allow section. Here I've set dependency-type to all, which means that subdependencies will also be updated. Without this, only explicitly defined dependencies will be updated.

Other configuration options are availble.

Adding this file is enough for dependabot to submit pull requests on your repo with package updates. We need to do a bit more to get them merging automatically. For this, we need GitHub Actions.


You should only have your dependencies merge automatically if you have an exhaustive CI set up. Otherwise, you may be vulnerable to obnoxious developers and supply chain attacks. Supply chain attacks may still get through your CI however, so you should judge the level of risk you're willing to tolerate.

We'll create a new file, .github/workflows/dependabot-automerge.yml.

name: Dependabot auto-merge
on: pull_request_target

  pull-requests: write
  contents: write

    runs-on: ubuntu-latest
    if: ${{ == 'dependabot[bot]' }}
      PR_URL: ${{ github.event.pull_request.html_url }}
      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
      - name: Dependabot metadata
        id: metadata
        uses: dependabot/fetch-metadata@v1.1.1
          github-token: "${{ secrets.GITHUB_TOKEN }}"
      - name: Approve PR
        run: gh pr review --approve "$PR_URL"
      - name: Merge PR
        if: ${{ steps.metadata.outputs.update-type != 'version-update:semver-major' }}
        run: gh pr merge --auto --squash "$PR_URL"

Exactly what you put in this file will depend on your workflow. For example, if your pull requests do not require reviews, you can omit that section. Are you feeling risk-averse? Remove the auto-merge, or use it only for patch versions. The opposite? Remove the conditional and auto-merge everything.

This example will approve every dependabot pull request, and merge any non-major semver versions automatically so long as all required checks pass. For major versions, I like to review them to make sure nothing will break. If the project isn't using semantic versioning, it's a little difficult to know what happens here, however. My assumption is that it'll do its best to figure it out and assume it's a major version. But it may be that if it doesn't look like it's using semver, it will not count as a major update and will be merged automatically. If anyone does know the answer to this, I would love to hear it. Luckily, most packages use something similarto semantic versioning these days so I haven't yet had any problems. I'll update this post if I notice any.

I hope this saves you some time you could be using for something more fun.