The great thing about SEO, in my opinion, is that there are so many resources that you can do nearly everything for free. Chalk it up to link-bait, but some of the best tools are actually free.
Here are a some free tools that I don’t see in the other answers:
Keyword and competitive research:
- UberSuggest: long tail keyword research. Keywords often don’t show up in Google’s keyword planner.
- Word Frequency Counter: good for competitive/keyword research
- Wayback Machine: check old or deleted pages on any website. Comes in hand for competitive research
- Builtwith: find out what websites are built with (CMS, etc.)
- APIs Dashboard: all of the most popular APIs on the web
- Draw.IO – draw simple charts and graphs
- Unsplash | Free High Resolution Photos – Free Stock images
- Infogram and Piktochart – create free infographics
- FindTheBest – great research search engine
- Butterick’s Practical Typography – learn typography
- Google Images: reverse lookup an image to find if an image or graphic you created has been used without attribution, then reach out to ask for a link.
- Google Alerts: Get alerts when a keyword is mentioned in content. Google for citation link building.
- SEOTools for Excel: Suite of tools, including pulling meta title, meta description of URL, checking HTTP status codes of URLs and more. A personal favorite.
- Screenfly: test your website on different devices and resolutions
- Ayima redirect path chrome extension: shows redirect path of any given URL
- Google Webmaster blog: not a tool, but contains the answers to some of the most difficult technical SEO questions