Both are made by leading SEO platforms — but they take completely different approaches to what a free extension should offer. Here's the honest breakdown.
| Feature | Ahrefs Toolbar | Semrush Toolbar | Winner |
|---|---|---|---|
| On-page SEO audit (free) | ✓ Full — titles, metas, H-tags, canonicals, robots | ✗ Not available free | Ahrefs |
| SERP overlay (free) | ✗ Paid only | ✗ Paid only | Neither |
| Redirect chain tracer (free) | ✓ Full chain | ✗ Not available | Ahrefs |
| Broken link checker (free) | ✓ | ✗ | Ahrefs |
| HTTP header reader (free) | ✓ | ✗ | Ahrefs |
| Country/language switcher (free) | ✓ 170+ countries | ✗ | Ahrefs |
| Core Web Vitals check (free) | ✓ | ✗ | Ahrefs |
| Authority metrics overlay | DR/UR — Ahrefs paid | AS — Semrush paid | Tie (paid) |
| SERP keyword difficulty | ✗ | ✓ Semrush paid | Semrush |
| Traffic estimates in SERP | Paid only | Paid only | Tie (paid) |
| No account needed | ✓ Full free features | ✗ Semrush plan required | Ahrefs |
| Firefox support | ✓ | ✗ | Ahrefs |
| Safari support | ✓ | ✗ | Ahrefs |
| Extension install price | Free | Free | Tie |
| Paid plan entry price | $29/month (Starter) | $117.33/month (Pro) | Ahrefs |
Both extensions install for free, but unlocking their full SERP overlays and authority metrics requires a paid plan. The pricing gap is significant.
Both Ahrefs and Semrush maintain large proprietary databases, but they measure different things with different methodologies.
Backlink data: Ahrefs' crawler is widely regarded as the largest and most frequently updated link index in the SEO industry. Domain Rating (DR) tends to reflect new links and lost links faster than Semrush's Authority Score (AS). For backlink analysis specifically, Ahrefs has the edge.
Keyword and traffic data: Semrush has strong keyword coverage, especially for US-focused research, and its traffic estimates are competitive. Neither tool uses actual Google data — both estimate from their own click-stream and crawl data. Treat both as directional indicators.
Practical implication: If your workflow is primarily backlink analysis, Ahrefs' data source is preferable. If keyword research and competitive traffic analysis is central, Semrush's dataset complements that work well. This applies to the full platforms, and by extension their toolbar extensions.