I want to share with you couple of free tools I use to spy on my competitors.
1. Majesticseo.com – Also in Free Version you can find your competitor backlinks & SEO links.
2. builtwith.com – Awesome tool to check your competitor site platform.
3. WhatWPThemeIsThat.com – Find out your competitor themes.
4. SpyOnWeb.com – Find out how many sites and domain names your competitors own.
5. Alexa.com – Analyze your competitor websites traffic.
6. Compete.com – Analyze your competitor US websites traffic.
7. SimilarWeb.com – Analyze your competitor websites traffic.
8. Spyfu.com – Analyze your competitor ad campaign.
9. DailyChanges.com – Find out which domains your competitor registered or drop.
Of course, there are a lot more tools out there. These are just some of my favorites. If you know a great free tool to spy on your competitor, please share it in the comments section below.