What are the best SEO tools for a startup?

I'm not necessarily sure there are tools that will directly affect your rankings. I guess if you're using Wordpress the Yoast plugin is pretty good for helping to analyze/correct/optimize the content you're creating. But tools like SEMRush or Moz really only provide data and you need to understand what things to do to act on that data. Honestly, creating quality content (& making sure it's being crawled properly) and building backlinks are the most important tools to ranking.

Good SEO tools are things like SEM Rush, Moz, ahrefs. That kind of thing. These tools are good for monitoring but they're not going to help you go up in the rankings, or get more traffic.

There are really only two ways to get better rankings and more traffic:

1. Produce good content that keeps people on your page/site for a long time.

2. Get quality backlinks.

If you do (1) correctly, (2) should follow without too much difficulty (aka some manual outreach).

The best tool for a small budget is ensuring that your on-page (or technical SEO) is in order. The best tools for that are page optimizer pro or SEO surfer, there is also CORA but its a lot more technical.

You should write case studies, how X used your product to get result Y.