How big of let down is it when you are reading a web page, find something interesting enough to click on and are subsequently dropped down the 404 Not Found hole?

Often the maintainer of a site does not even know what is broken – especially for content oriented sites which have a healthy amount of outbound links.

Much like broken and flaky tests, compiler warnings, test coverage, code quality and consistent configuration+tooling across promotion environments, the sooner you establish  [Picard voice] "the line must be drawn here", the better off you are.   Once you have a set standard of what is acceptable and good visiblity to what is crossing that line, you have a fighting chance of understanding where to invest to maintain that standard or improve it.

For a blog like this one, hyperlinks can break a few different ways.   Internal links can be broken from the start due to unforced errors (i.e. - typos) or software upgrades.  Links going out to other sites can drift into a broken state due to an external site making changes or being taken offline.


I wanted to see how this site was doing and had recently stumbled on Muffet, a supa-fast, open source, Go-based broken link checker.  

The first time I ran Muffet, I discovered an embarrassingly long list of broken links here.

Here are some choice examples from a trimmed down version of that first run:

$ muffet


How to read this output: By default, Muffet only puts broken links in the output.  Hierarchy is expressed through indention:  so #97 above is a link that was walked while parsing the page at #96.   The unindented number is a counter of links checked, and the indented numbers are HTTP return codes (404 = not found).  

All of the link issues above were unforced errors as far as I can tell.   Additionally, the stuff I trimmed out included errors for images that had gone missing and links to external sites that were no longer valid.  

Awesome!  We now have a way to assess the whole site for broken links.  The problem is we just found a whole bunch of broken things all at once, which means a whole bunch of work to fix them.

Prefer small fixes right away

Next time a link breaks, I want to be fixing just that one thing and be done -- rather than looking at a large pile of issues that have accumulated over a longer period of time.

Ideally, I want broken links assessed:

  • Automatically, before publishing new content – to catch unforced errors before they go live
  • Automatically, on configuration changes and software upgrades – to catch unexpected interactions of new software and existing content
  • Automatically, on a schedule – to catch drift in the health of links to external party sites
  • On demand, to confirm I have fixed issues after making changes

Having a place to trigger the workload which executes a broken link checker manually or programmatically, record the results, and notify me when things break would hit all my needs.

After my other recent experiment with a Github Action, that seemed like a good candidate.

A Github Action for Muffet

Always Google first, to see if someone else has already done similar work.

I found an archived Github repo from peaceiris that had a Muffet Github action. I have no idea why he/she archived it, but it seems to work fine, so I forked it to keep a copy.

To use that action from our project [checked in to a Github repo], I added a workflow at .github/workflows/checklinks.yml :

name: checklinks

on: [push]

    runs-on: ubuntu-latest
    - name: Check links on site
      uses: mattorb/actions-muffet@v1.3.1
        args: >
          --timeout 20 

This sets up triggering Muffet to check for broken links on every push to git master.  It builds the needed action via a Docker build of the Github repo mattorb/actions-muffet, tag 1.3.1.

As noted earlier, sometimes external links go bad due to changes outside our  awareness, so below we add a schedule stanza to trigger this check regularly as well:

name: checklinks

    - master
    - cron:  '0 13 * * 6'

    runs-on: ubuntu-latest
    - name: Check links on site
      uses: mattorb/actions-muffet@v1.3.1
        args: >
          --timeout 20 

Now, in addition to executing on pushes to master, that cron schedule sets this check to happen automatically once a week. ('0 13 * * 6' == 1pm on Saturdays)

When it fails, Github sends you an e-mail.  (default settings)

Also, this handy badge can be placed at the top of in the git repo, or on the site itself:

Github Action Build Status

That badge is live, so hopefully it reads 'passing' when you are reading this article!  For how to make one, see the Github docs.

At this point, we have a Github Action in place that will be kicked off for a few scenarios:

  • Manually triggered via the Github web UI
  • Automatically triggered via the a push the git repo master
  • Automatically triggered once a week

For all the ways you can trigger Github Actions, see here.  

Going Further

One of those GitHub Action triggers that I'm particularly interested in, since my blog workflow has not moved over to a static generation approach yet: repository_dispatch.  It is still in developer preview but offers a way to trigger a Github Action workflow based on an external events.  

Ghost has webhooks that can be triggered for various types of modifications:

Tying one or more of those to triggering the Github Action via a repository_dispatch event will require building something to either receive the Ghost JSON webhook Payload and post the Github expected JSON payload, or extending Ghost itself with a custom webhook integration for repository dispatch – a small future project.  

UPDATE: here is a quick stab at that in Go.  I point Ghost webhooks at it for the 'New post published' and 'Published post updated' events to trigger broken link checking on those two events.   It is a bit naive in that it scans the whole site every time a new post is published.