There is no single best keyword research tool, but there is an order most small sites should try things in, and it starts with two free sources almost everybody skips past on the way to a subscription. The ranking below is by what you should reach for first given what it costs you and what it answers, not by how much data each one holds. Nobody paid to be here and none of these links are affiliate links.
The best keyword research tools: the ranking, and the criterion
- Google Search Console: Free, and the only source with your own impressions, clicks and average positions in it. Start here on any site that already has pages indexed, because the queries you nearly rank for are usually the cheapest work available.
- Google Keyword Planner: Free with a Google Ads account and the standard free source for queries your site does not yet appear for. It reports ranges rather than exact volumes unless you are actively spending, which is enough to sort candidates by order of magnitude.
- A paid keyword database: Worth it once you need queries you would not have thought of, coverage of pages that are not yours, or difficulty modelling over thousands of rows. Judge one on how stable its ordering is and on whether you can export everything, not on how many keywords it claims to hold.
Start with the queries you already appear for
Before buying anything, look at what your site already shows up for. Those queries come with your own click and impression data attached, which no third-party estimate can match, and the ones sitting just off the first page are usually the cheapest wins available to you. A great deal of keyword research on an existing site is really this, done properly once.
Then get ranges for the queries you do not have yet
For anything your site does not appear for, you need an outside source, and the free one is Keyword Planner. It gives ranges rather than exact numbers unless you are spending on ads, which is enough to sort candidates into orders of magnitude. Sorting by magnitude is all most decisions require, and a range you understand beats a precise number you do not.
Only then consider paying for an index
A paid database earns its money when you need queries you would not have thought of, competitor coverage, or difficulty modelling across thousands of rows. That is a real need at some scale. It is not a starting need, and starting there is why so many small sites pay monthly for a tool they open twice a year.
Whatever you use, keep the decision somewhere
The tools above answer what exists and roughly how big it is. None of them holds the thing you actually produce: this query is worth writing, it belongs on that page, here is where it sat last month. That record is what turns research into work, and it is the part that gets rebuilt in a spreadsheet every time.
Questions people ask about the best keyword research tools
Is there a genuinely free keyword research tool?
Two, and they answer different halves: Search Console for queries you already show for, Keyword Planner for queries you do not. Together they cover most of what a small site needs.
Why is no paid tool ranked first here?
Because for a small site the free sources answer the first questions, and paying before you have exhausted them buys data you are not yet using.
Do the volumes from these tools agree?
No, and they are not meant to. Each models from its own data. Pick one source per list and use the ordering rather than the absolute numbers.
How was this ranked?
By what a small site should reach for first, given the cost of starting and what the tool answers. Nobody pays to appear here and the reason for each place is written above.