You can do the whole of keyword research for a small site without paying anybody, and most people who end up paying never exhausted the free sources first. What free gives you is real data about your own site, ranges rather than exact figures for everything else, and none of the convenience: more steps, more exporting, more of your own judgement. For a list of a few dozen queries that trade is usually worth making.
Your own queries, free and better than any estimate
Search Console gives every query your site received impressions for, with clicks and average position, at no cost. For an existing site this is the most valuable keyword data available to you and it is not an estimate of anything: it is what happened. The queries sitting just off the first page are visible here and nowhere else, and they are usually the cheapest work available.
Ranges for queries you do not have yet
Keyword Planner is free with a Google Ads account and gives volume in bands unless you are spending on ads. Bands are enough: the decisions you make from volume are about orders of magnitude, and treating a precise-looking number as precise is a mistake anyway. It will also suggest related terms, which covers the expansion step that generators are sold for.
What free will not give you
Competitor coverage, because you cannot see another site's Search Console. Difficulty modelling across thousands of rows. Automated position checks on a schedule from a chosen place. Historical trend at query level beyond the window the free tools keep. Each of those is a real thing to want at some point, and none of them is a starting need.
The step that costs nothing and gets skipped
Scoring the shortlist on your own conversion rate and value per conversion needs no subscription at all, and it is the step that changes decisions most often. The free worksheet on this site does exactly that, in your browser, without an account, because the arithmetic is not the part anybody should be charging for.
Questions people ask about free keywords search
Can I do keyword research for free?
For a small site, yes: Search Console for your own queries, Keyword Planner for the rest, and your own arithmetic to decide between them.
Is Keyword Planner free?
It comes with a Google Ads account at no cost, and reports volume as ranges rather than exact figures unless you are actively spending.
What is the catch with free tools?
More steps and less convenience, plus no competitor data and no scheduled rank checks. The data you get about your own site is excellent.
Do I need an account for the worksheet here?
No. It runs in your browser and the figures are not sent anywhere unless you choose to save them.