7 Best Keyword Research Tool API in 2026 (Free and Paid, Compared)
7 best keyword research tool API options compared on price, API limits, keyword data and free tiers. Every price checked on the vendor page, November 1, 2026.
Shamim Mia, Founder, SerpAstraLast verified November 1, 202612 min readWe compare pricing pages, documentation and public reviews. We never accept payment for rankings.
Key takeaways
- DataForSEO is the best pick for pure API use: pay-as-you-go from a $50 top-up, no subscription. Ahrefs (Lite, $129/month) and SE Ranking (Core, $129/month) are the best suite APIs.
- The single most important buying factor is how the vendor meters usage — per task, per unit, per row or per request — because that decides the real bill, not the headline price.
- Free options exist — DataForSEO gives a $1 trial credit and a free Sandbox, Moz has a free API tier — but serious volume always needs a paid plan.
- Semrush has the largest keyword database here, but its API sits behind a custom-quoted Advanced plan and the unit balance starts at zero.
- Every price below was checked on the vendor's own pricing page on November 1, 2026. Ratings are G2, with review counts shown; the Moz API has no separate G2 profile, so it shows no rating.
On this page
Quick comparison
| Tool | Best for | Starting price | Free plan |
|---|---|---|---|
| DataForSEO | Developers and SEO tool builders who want raw keyword data on demand without a monthly subscription | $50 top-up (PAYG) | Yes ($1 credit) |
| Ahrefs | In-house SEOs and agencies that already use Ahrefs and want keyword data next to backlink data | $129/mo | Yes (test queries) |
| SE Ranking | Small agencies and in-house teams that want API access bundled with a full SEO suite | $103.20/mo (annual) | No (14-day trial) |
| Serpstat | Small agencies and freelancers who want a low-cost suite API with generous credit limits | $50/mo (annual) | Yes (no API) |
| Keyword Tool | Content teams and indie SEOs who need long-tail keyword ideas from autocomplete across many platforms | $88/mo | Yes (no volume) |
| Semrush | Enterprises and agencies already on Semrush that need its keyword database in their own systems | Custom quote | Yes (no API) |
| Moz API | Agencies and tool builders that need Domain Authority and link metrics in client reports | $20/mo | Yes (50 rows/mo) |
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Request a listingThe best keyword research tool API
DataForSEO
Best for: Developers and SEO tool builders who want raw keyword data on demand without a monthly subscription
DataForSEO is the only pure API in this list, and that is why it leads it. There is no dashboard to learn and no seat to pay for: you top up $50, call the Keywords Data API, and pay from $0.0012 per task for search volume, trends and advertising data from Google Ads, Google Trends and Bing Ads. The balance never expires, so a quiet month costs nothing.
The trade-off is that you build everything yourself. There is no rank tracker or keyword interface, so a non-developer gets nothing usable out of the box, and per-task pricing needs a cost model before you scale. If you can write code — or plug the API into n8n, Make or Sheets — it is the cheapest route to production keyword data.
What we like
- Pay-as-you-go with no subscription and a balance that never expires
- Keywords Data API from $0.0012/task, with Google Ads, Google Trends and Bing Ads sources
- Live and Standard request modes plus a Sandbox and an API Playground for testing without code
Watch out for
- No dashboard product — you build the interface yourself, so it is not a tool for non-developers
- Per-task pricing needs a cost model before you scale, or a big pull can surprise you
Ahrefs
Best for: In-house SEOs and agencies that already use Ahrefs and want keyword data next to backlink data
Ahrefs is the choice when keyword data has to sit next to backlink and traffic data from the same index. The API is included from the $129 Lite plan with 200,000 units a month, and Keywords Explorer draws on a 110-billion-keyword database — the deepest in this list. You can query Site Explorer, Keywords Explorer and the rest programmatically on a normal subscription, with no separate API contract.
The constraint is rows, not calls. Lite caps each request at 100 rows, so a pull of a thousand keywords is ten round trips, and Starter at $29 only gets free test queries. If you already pay for Ahrefs, the API is an easy yes; if you only need keyword data, DataForSEO costs less.
What we like
- Keywords Explorer draws on a 110-billion-keyword database, the deepest here
- API and MCP access included from Lite, with 200,000 API units a month
- Every request costs at least 50 units, so small lookups stay cheap
Watch out for
- Starter ($29/month) gets test queries only — real API use starts at Lite ($129/month)
- 100-row cap per request on Lite turns big keyword pulls into many calls
SE Ranking
Best for: Small agencies and in-house teams that want API access bundled with a full SEO suite
SE Ranking is the value pick for teams that want an API and a suite in one subscription. API access comes with every plan — Core costs $129 a month and includes 25,000 API credits — and a pay-as-you-go route starts with a $50 deposit for 250,000 credits that never expire. The same plan covers rank tracking, audits and AI visibility, so one subscription replaces two or three.
The credit allowance is the honest limit. Core's 25,000 credits cover steady research but not bulk pulls, and white-label reports need the Agency Pack add-on. Pick SE Ranking when you want the API inside a suite you already use daily; pick DataForSEO when you only need raw data.
What we like
- API access and MCP included in every plan, with 25,000 credits on Core
- Pay-as-you-go API from a $50 deposit for 250,000 credits that never expire
- AI visibility tracking across 5 engines included on Core (25 prompts a day)
Watch out for
- Core's 25,000 API credits run out fast on bulk keyword pulls
- White-label reporting needs the $69/month Agency Pack add-on, not the entry plan
Serpstat
Best for: Small agencies and freelancers who want a low-cost suite API with generous credit limits
Serpstat is the cheapest suite API in this list, and the credit allowance is the reason. Individual costs $69 a month and includes 100,000 API credits a month — four times what SE Ranking's Core plan gives for nearly twice the price — plus a keyword database covering 230 countries and the full suite of rank tracking, audit and backlink tools.
The catch is that the free plan cannot touch the API, so there is no free way to test it in production, and reviewers rate the keyword data a step below Ahrefs and Semrush. For a small agency that wants a lot of API calls for little money, it is the best value here; for the deepest data, look at Ahrefs instead.
What we like
- 100,000 API credits a month on Individual — the most generous entry allowance here
- Keyword database covers 230 countries
- Full suite (rank tracking, audit, backlinks) rides along for $69/month
Watch out for
- API access needs a paid plan — the free plan cannot call it
- Keyword data accuracy trails Ahrefs and Semrush in reviewer comparisons
Keyword Tool
Best for: Content teams and indie SEOs who need long-tail keyword ideas from autocomplete across many platforms
Keyword Tool is the long-tail specialist in this list. Its API mines autocomplete from Google, YouTube, Bing, Amazon, eBay, app stores and more, and returns search volume sourced directly from Google and Bing Keyword Planner — so the numbers match what the planners show. One search-volume request takes up to 1,000 keywords, which keeps request counts low.
The limit is the daily cap. Starter allows 50 requests a day across the web interface, API and MCP combined, which is fine for content planning and tight for bulk pipelines. There is also no keyword difficulty score and no backlink data. Buy it for ideas and volumes across platforms, not as your only SEO data source.
What we like
- Search volume sourced directly from Google and Bing Keyword Planner
- Suggestions from Google, YouTube, Amazon, eBay, app stores and more in one API
- Up to 1,000 keywords per search-volume request
Watch out for
- 50 requests a day on Starter is a hard ceiling for bulk work
- No keyword difficulty score and no backlink data
Semrush
Best for: Enterprises and agencies already on Semrush that need its keyword database in their own systems
Semrush has the largest keyword database in this list — its Keyword Magic Tool draws from more than 27 billion keywords across 140-plus countries — and one API key covers keyword, domain, backlink and traffic data. If your team already lives in Semrush, the API puts that data into your own dashboards and AI assistants without a second vendor.
The floor is the problem. REST API access sits on the Advanced plan, which Semrush now prices by quote, and the plan alone starts you at zero API units — units are a second purchase whose price is not published. Get the quote and the unit price in writing before you scope a build around it.
What we like
- Keyword Magic Tool draws from a 27-billion-plus keyword database across 140+ countries
- One API key covers keyword, domain, backlink and traffic data
- MCP access brings Semrush data into AI assistants
Watch out for
- REST API sits on the Advanced plan, which Semrush now prices by quote
- The plan buys permission only — the unit balance starts at zero and units are a second purchase
Moz API
Best for: Agencies and tool builders that need Domain Authority and link metrics in client reports
The Moz API is the cheapest paid API in this list, and it is also the narrowest. Starter costs $20 a month for 3,000 rows, and a free tier covers 50 rows a month at one request every 10 seconds. What it returns is what Moz is known for — Domain Authority, Page Authority, Spam Score and link metrics — the numbers clients already ask for by name in reports.
Be clear about the scope before you buy. This API returns links and authority, not live SERP data, and keyword research lives in Moz Pro, a separate subscription. It has no separate G2 profile, so this card shows no rating. Use it as a cheap authority feed next to a real keyword API, not as your keyword source.
What we like
- Cheapest paid API here — Starter is $20 a month, with a free tier of 50 rows a month
- Domain Authority and Page Authority are the metrics clients already ask for by name
- No-overage policy on the free tier, so testing costs nothing
Watch out for
- Links and authority only — no live SERP data and limited keyword volumes
- Free tier allows one request every 10 seconds, which rules out bulk work
What the best keyword research tool API actually does
A keyword research tool API gives your software the same keyword data a dashboard shows a person: search volume, keyword ideas, difficulty, cost per click and competitor keywords, returned as structured data your code can use. The best keyword research tool API for you depends on what you build with it — a content planner needs ideas and volumes, a reporting tool needs competitor keywords, and an internal dashboard needs all of it on a schedule.
The scale of the data behind these APIs is large. Semrush says its Keyword Magic Tool draws from more than 27 billion keywords across 140-plus countries, and Ahrefs puts its keyword database at 110 billion keywords. That index size is what you are paying for: a bigger database means more long-tail ideas and more accurate volumes for the keywords your buyers actually search. If you would rather have that research done for you, our SEO audit service turns keyword data into a prioritised fix list.
API-first or suite API
The 7 tools in this list split into two camps. The API-first camp has one member: DataForSEO, a pure data API with no dashboard and no subscription. You pay per task, the balance never expires, and you build whatever interface you need on top. It is the right camp when the API is the product — you are building a tool, a report or an automation.
The suite camp — Ahrefs, SE Ranking, Serpstat, Semrush and Moz — sells the API as part of a subscription you may already pay for. The API is a feature of the suite, metered in units, credits or rows, and the dashboard comes with it. Keyword Tool sits between the camps: a keyword specialist whose API shares its plan with the web tool. The right camp depends on whether you need the dashboard too: if you do, a suite API costs less than a separate API plus a separate tool.
Free tiers and trials first
Before you pay, check what you can test free. DataForSEO gives new accounts a $1 trial credit and a free Sandbox that returns sample responses without spending balance, and the Moz API has a genuinely free tier of 50 rows a month. Keyword Tool and Serpstat let you use their web tools free, but API access needs a paid plan, and SE Ranking's 14-day trial includes API access so you can test the real thing.
Free tiers are for testing, not production. Fifty rows a month or a dollar of credit will not run a keyword pipeline, and the moment you pull real volume, a paid plan is cheaper than the time you lose to workarounds. Use the free tier to prove the data matches your expectations — compare the volumes against Google Keyword Planner and Search Console — then pay for the plan that fits your volume.
How the meters compare
Every API in this list bills differently, and the meter matters more than the plan price. DataForSEO charges per task — a Keywords Data search-volume task starts at $0.0012 — so your bill follows the number of tasks, not the month. Ahrefs charges per unit with a 50-unit minimum per request, and Lite includes 200,000 units a month. SE Ranking and Serpstat charge per credit, with 25,000 and 100,000 credits a month on their entry plans. Keyword Tool charges per request, with 50 a day on Starter. Moz charges per row, with 3,000 rows a month on Starter. Semrush charges per line returned — 10 units for a live line, 50 for a historical line — and the units are a separate purchase.
The practical move is to price one real job. Take the 1,000 keywords you actually pull each month, work out how many tasks, units, credits, requests or rows that job needs on each API, and multiply. A plan that looks cheap per month can be dear per keyword, and a plan that looks dear can be cheap if its meter is generous. Do that math once, before you commit, and the right API usually picks itself.
Quick comparison: tool type by need
| Buyer | Best pick | Why |
|---|---|---|
| Building a tool or automation | DataForSEO | Pay-as-you-go from a $50 top-up, no subscription, balance never expires |
| Already paying for a suite | Ahrefs or SE Ranking | API included from Lite/Core at $129/month with units or credits in the plan |
| Cheapest suite API | Serpstat | 100,000 API credits a month from $69/month |
| Long-tail ideas, many platforms | Keyword Tool | Autocomplete suggestions from 16 platforms with exact Planner volumes |
| Biggest keyword database | Semrush | 27-billion-plus keywords, but API access is custom-quoted |
| Authority metrics on a budget | Moz API | Domain Authority and link data from $20/month, with a free tier |
How to choose: a short decision path
- Count your monthly volume first. Under a few hundred lookups, the free tiers and DataForSEO's $50 top-up cover you. Over tens of thousands, the per-unit price decides — compare the cost of one keyword across vendors, not the headline plan price.
- Check what counts as one unit. DataForSEO bills per task, Ahrefs per unit with a 50-unit minimum, Moz per row, Keyword Tool per request. The same pull can cost very different amounts depending on the meter.
- Decide API-first or suite. If you need the dashboard too, a suite API is cheaper than two subscriptions. If you only need data in your own system, a pure API costs less.
- Test the data before you commit. Pull the same 100 keywords from your top two picks and compare volumes against Google Keyword Planner. If the numbers disagree, trust the planner and pick the closer API.
- Check the rate limits. Row caps per request, requests per day and requests per 10 seconds all shape how fast you can pull. Keyword Tool's 50 requests a day and Moz's 1 request per 10 seconds on the free tier are real ceilings.
Before you build content around the keywords you pull, run your titles through the free keyword density checker — it shows whether the page actually uses the terms you targeted.
Mistakes to avoid
- Comparing plan prices without checking the meter. A $69 plan with 100,000 credits can be cheaper than a $129 plan with 25,000 credits if you pull in bulk.
- Assuming the plan includes units. Semrush starts your API balance at zero after the upgrade — the plan buys permission, and the units are a second purchase.
- Ignoring the rows-per-request cap. Ahrefs Lite caps requests at 100 rows, so a thousand-keyword pull is ten calls. Budget the calls, not just the units.
- Buying an API when you need a dashboard. If nobody on your team writes code, an API key is useless — buy the tool, not the data feed.
- Trusting a directory price. Serpstat's pricing page returned an error to our checker, so we confirmed its $69 Lite price against G2's vendor-supplied pricing and several directories. Always check the vendor's own page before you buy.
How we chose
We checked each vendor's own pricing page on November 1, 2026 and recorded the starting price exactly as shown, including the annual-billing figure where the page lists one. Two prices could not be read directly from the vendor page: Serpstat's pricing page returned an error, so its $69 Lite price rests on G2's vendor-supplied pricing and several directories; Keyword Tool's Pro page was rate-limited, so its $88 Starter price rests on an October 2026 third-party read of the vendor page. Semrush now prices its API plan by quote, so we list it as a custom quote rather than a stale $549 figure. Ratings come from G2, except the Moz API, which has no separate G2 profile and shows no rating. We ranked the tools by fit for the most common buyer — a developer or SEO team pulling keyword data into their own workflow — not by brand size. No vendor paid for a place in this list, and none of the links here are affiliate links.
What to do next
Start with the decision path above: count your monthly volume, learn how each vendor meters it, and decide API-first or suite. Then take the free tier or trial of your top pick and pull the same 100 keywords you care about most, comparing the volumes against Google Keyword Planner. If the numbers match and the meter fits your budget, you have your API. If you'd rather have this set up and read for you, request a free SEO + AI visibility audit and get a ranked fix list in 2 business days.
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Get a free SEO + AI visibility audit→Sources we checked (18)
- DataForSEO pricing — dataforseo.com/pricing (checked November 1, 2026)
- DataForSEO on G2 — 4.4/5, 17 reviews (checked November 1, 2026)
- Ahrefs API — ahrefs.com/seo-api (checked November 1, 2026)
- Ahrefs pricing — ahrefs.com/pricing (checked November 1, 2026)
- Ahrefs on G2 — 4.5/5, 723 reviews (checked November 1, 2026)
- SE Ranking API — seranking.com/api.html (checked November 1, 2026)
- SE Ranking pricing — seranking.com/subscription.html (checked November 1, 2026)
- SE Ranking on G2 — 4.7/5, 1,619 reviews (checked November 1, 2026)
- Serpstat pricing — serpstat.com/pricing (checked November 1, 2026)
- Serpstat on G2 — 4.6/5, 466 reviews (checked November 1, 2026)
- Keyword Tool API docs — keywordtool.io/api (checked November 1, 2026)
- Keyword Tool Pro pricing — keywordtool.io/pro (checked November 1, 2026)
- Keyword Tool on G2 — 4.5/5, 19 reviews (checked November 1, 2026)
- Semrush pricing — semrush.com/prices (checked November 1, 2026)
- Semrush on G2 — 4.4/5, 4,304 reviews (checked November 1, 2026)
- Semrush Keyword Magic Tool database — 27 billion+ keywords, 140+ countries (Semrush, via G2)
- Moz API pricing — moz.com/products/api/pricing (checked November 1, 2026)
- Moz Pro on G2 — 4.3/5, 608 reviews (the Moz API has no separate G2 profile; checked November 1, 2026)
Shamim
Founder of SerpAstra
A full-stack SEO and digital marketer who spends most days on Local SEO for dental practices, AI search visibility and lead generation.
Frequently asked questions
What is the best keyword research tool API in 2026?
DataForSEO is the best pick for pure API use: pay-as-you-go from a $50 top-up, with no subscription and a balance that never expires. If you already pay for Ahrefs or SE Ranking, their bundled APIs are the better buy — Ahrefs from Lite at $129/month, SE Ranking from Core at $129/month.
How much does a keyword research API cost?
From a $50 one-time top-up with DataForSEO to $129 a month for the suite APIs from Ahrefs and SE Ranking. Serpstat starts at $69 a month, Keyword Tool at $88, and the Moz API at $20. Semrush prices its API access by quote, and its units are a second purchase on top of the plan.
Is there a free keyword research API?
There is no free API with production volume. DataForSEO gives new accounts a $1 trial credit and a free Sandbox, and the Moz API has a free tier of 50 rows a month. Keyword Tool and Serpstat let you use their web tools free, but API access needs a paid plan.
What is the difference between a keyword research API and a keyword tool?
A keyword tool is a dashboard a person uses; an API is the same data served to software, so your own product or workflow can pull it. APIs are metered — per task, unit, row or request — and most need a developer to set up. If nobody on your team writes code, buy the dashboard, not the API.
Which keyword API has the largest keyword database?
Ahrefs, at 110 billion keywords, and Semrush, at more than 27 billion keywords across 140-plus countries. DataForSEO and Serpstat do not publish a single comparable database size, and Keyword Tool's volumes come straight from Google and Bing Keyword Planner rather than a proprietary index.
Do I need a subscription or can I pay as I go?
Both exist. DataForSEO is pay-as-you-go with a $50 minimum top-up, and SE Ranking offers a pay-as-you-go API from a $50 deposit for 250,000 credits. Ahrefs, Serpstat, Keyword Tool, Semrush and Moz all bill monthly, with annual billing cheaper on most suite plans.
What should I check before buying keyword API access?
Four things: what counts as one billable unit and what it costs, the rate limit and rows-per-request cap, whether the plan includes any units or starts at zero, and whether the data covers your countries. All four vary widely — the comparison table at the top of this guide shows the starting price and free tier for each tool.
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