Find broken links before
your users do.
4F continuously monitors your site for broken links, failing assets, missing anchors, redirect chains, and SSL issues. With a bit of SEO fluff.
No account needed · up to 1,000 pages · 2 free scans per day
By clicking “Scan now” you agree to our Terms of Service.
What 4F detects
The broken link checker that works while you sleep
Broken links, missing images, and dead-end redirects happen constantly – pages get renamed, third-party URLs go offline, assets get moved. 4F crawls your entire site and surfaces every issue so you can fix them before your users – or search engines – notice.
Domain health & blacklist check
Before your users land on your site, 4F checks whether your domain has been flagged by major threat intelligence databases. A clean scan means links work – a healthy domain means it's safe to visit.
Available on every project, no configuration needed. Results are shown alongside your server details and refresh whenever you trigger a lookup.
Built by developers, shared with everyone
4F started as an internal tool – something we built to check our websites before and after going live. It grew into something we used on every project, every deploy. At some point we realised: why keep it to ourselves?
So we opened it up. The free tier isn't a crippled trial or a bait-and-switch – it's a genuinely useful tool, no credit card required. We think that's how it should be.
Add it to your build pipeline. Run it when you deploy. Let it catch what you missed. We call it foureffing a site – and we do it on everything we ship.
Pricing
- + 10,000 pages/month
- + Up to 3,000 pages per scan
- + 2 projects
- + Manual scans
- + 7-day scan history
- + API access
- + Webhooks
- + CSV export
- + No credit card, ever
- + 50,000 pages/month
- + Up to 10,000 pages per scan
- + 10 projects
- + Weekly scan schedule
- + Email alerts
- + 30-day history
- + Up to 10 req/s crawl speed
- + Priority crawler – no queue wait
- + Sitemap.xml support
- + No domain restrictions
- + 500,000 pages/month
- + Up to 50,000 pages per scan
- + 50 projects
- + Daily scan schedule
- + 90-day history
- + Up to 15 req/s crawl speed
- + Dedicated crawler
- + 5 team seats
No credit card required
Common questions
Is 4F free?
Yes. The free plan is genuinely free - no credit card, no trial, no time limit. You get up to 10,000 pages per month and can scan up to 3,000 pages in a single scan. No account is required for a quick one-off scan of up to 1,000 pages.
How many pages can 4F scan?
Up to 1,000 pages without an account, 3,000 per scan on the free plan, 10,000 on Starter, and 50,000 on Agency. Only internal HTML pages count toward your quota - external links and assets are checked but do not consume quota.
Does 4F work with JavaScript-rendered sites?
4F is a server-side crawler and does not execute JavaScript. It works well with server-rendered sites (WordPress, static HTML, Next.js with SSR) but cannot discover links injected by JavaScript in the browser. For SPAs that generate a sitemap at build time, you can point 4F at the sitemap (Starter plan and above).
How often can I run scans?
As often as you like on demand on all plans. Paid plans add scheduled scanning: weekly on Starter, daily on Agency. You can also trigger scans via the REST API or the official CLI.
What types of issues does 4F detect?
Broken links, failing assets, broken anchor targets, redirect chains, slow responses, SSL errors, mixed content, SEO issues (title, H1, meta description, alt text, and more), and domain blacklist status across Google Safe Browsing, VirusTotal, URLhaus, and Spamhaus.
More questions? See the full FAQ.