Not every free crawler is the same. There is 'free that works' and then there is 'free that is actually a 500-URL trial before hitting a paywall'. This list distinguishes between the two. Every tool listed here is one I have run a full audit with, and I have mentioned where the free portion stops. We make the first of these, so feel free to skip it — otherwise it's the same list I would give a workmate asking for a suggestion.
If you want a tool that is completely free and works in your web browser then you should start with AlphaCrawler. No downloads, no installations — just paste in a URL and let the crawl complete on remote servers so as not to slow down your laptop. You end up with a report, which has its own URL, that you can share with the developer, client or other stakeholders in an organisation. The crawler covers all of the common things you would want to audit from a technical SEO point of view, including broken links, status codes, redirect chains, internal and external links, and metadata issues such as missing and duplicate page titles, descriptions, canonicals or H1 tags that repeat themselves across multiple pages or are missing from template code. The free portion is the crawler in the browser; there are higher limits for pages, URLs and number of projects on the paid plans, and the crawler is not designed for large-scale enterprise-level crawls or to pull custom data points.
A very common tool that many people learn on first. Its free crawler will do 500 URLs, which is good for a small site or if you just want to audit a small section. Because this is a desktop crawler, it relies on your own machine to do the crawling and can take a long time for larger numbers of URLs, as well as taking up more memory. If you go over the limit of 500 URLs you can buy an annual licence for £199 which will let you crawl as many URLs as you want. It is a great tool to use for in-depth desktop audits and for crawling that involves custom extraction and integration with Analytics and Search Console.
The most similar competitor to Screaming Frog. Sitebulb is very good at explaining how you can rectify the technical errors found in a crawl. The main downside is that you only get access to a trial version rather than free access to the crawler, so this is really a tool to try before committing to a subscription. If you would like your team to have a guided and prioritised audit, complete with visuals to help explain things in a non-SEO way, Sitebulb is a great option to try out.
Free to use, it will crawl a large number of URLs. As a desktop crawler you will need to download and install it, and you have limited access to save and download the results. That aside, this crawler gives you full crawling and issue identification, which is far more useful than a teaser version. It's a great way to get a genuinely useful crawler that runs on your laptop without an upfront cost, as long as you don't mind the limits on saving and exporting.
This is the open-source option on the list. It describes itself as the open-source competitor to Screaming Frog and can handle unlimited crawling and will render JavaScript. You will need to download it, and the tool is free in the real definition of the word because the code is open-source and free to view. As with all open-source tools, you are responsible for running and managing the crawler, making this a great option for a developer who wants an unlimited crawler they are in full control of — but not for someone looking for a click-a-button-and-be-done crawler.
Seobility, Sitechecker, Seomator and other sites are good for one-off page audits on any website without the need to download anything. However, it's a tough job finding a web audit tool with unlimited crawling and no restrictions. Most free SEO crawl tools will let you audit either just one page or a very limited website before asking for an email address and steering you toward a monthly subscription if you want to do a multi-page crawl, crawl multiple websites, or run regular audits.
If you want to run in-depth audits with a desktop crawler and you don't mind paying for a licence, both Screaming Frog and Sitebulb offer that. If you want an open-source, free-to-use and unlimited crawler, LibreCrawl is the option you can download and do as you wish with on your own machine. Or, if you want to run a crawl in your browser, get a report you can share, and avoid the download and installation step entirely, AlphaCrawler is the perfect tool to try first — start your crawl and in a couple of minutes you'll have a fully shareable report to review with a development, management or client team.
But in all honesty, most people looking to run a technical SEO audit will rarely need a crawler that goes over and above what a free one can do. You just need a tool that is light, can audit a handful of common technical issues, and can share the results with someone who has no time for the inner workings of a crawl. Try the free website crawler or the broken link checker to see the report format.