The best keyword research APIs for developers in 2026

The main keyword research APIs in 2026 are DataForSEO, Semrush, Ahrefs, SE Ranking, the Google Ads API, Keyword Tool, Serpstat and Cite42. DataForSEO is the cheapest way to pull search volumes in bulk. Semrush and Ahrefs suit teams that already pay for those suites, SE Ranking and Serpstat add keyword difficulty, and Keyword Tool covers YouTube and Amazon as well as Google. Cite42 returns monthly search volume, CPC and keyword ideas per API call, with no subscription and nothing to set up beyond an API key.

Cite42 publishes this guide. The Cite42 examples are real requests from October 5, 2026. We researched the other APIs from their official documentation and pricing pages on October 6, 2026, without paid test calls.

The best keyword research APIs for different jobs

• Cite42: search volume, CPC and ideas for 2 to 50 keywords per call, billed per call with no subscription. The same tools work over MCP in Claude, ChatGPT, Codex and Cursor.
• DataForSEO: the lowest cost per keyword for large batches, plus a big catalog of other SEO APIs.
• Semrush and Ahrefs: keyword data and difficulty from an SEO suite you already pay for.
• SE Ranking: volume, difficulty and search intent on pay-as-you-go credits.
• Google Ads API: first-party Keyword Planner data, once Google approves Basic access.
• Keyword Tool: bulk volume lookups and keyword ideas for YouTube, Amazon and other platforms.
• Serpstat: keyword difficulty next to domain and backlink data on a monthly plan.

Comparison at a glance

Sources are linked in each section. A per-call price, a minimum deposit and a monthly plan pay for different things, so compare them against how many keywords you check each month.

Cite42: keyword volumes per call with no subscription

Cite42 is a pay-per-call API and MCP server for keyword data, Google Trends and AI visibility. You get real monthly search volume, CPC and competition from one REST call, without creating a Google Cloud project, setting up OAuth or waiting for Google to approve API access. There is no subscription and no monthly fee: you top up a prepaid balance (minimum $25.00), the balance never expires, and you pay only for successful calls. A verified signup adds $1.00 of free credit.

A batch of 2 to 50 keywords in one country costs $0.09 when any keyword returns volume, or $0.03 when none do. A single keyword costs $0.09, or $0.12 with up to 50 related keyword ideas. Each row returns the requested keyword, its status (exact or no_data), average monthly volume, CPC and paid-search competition.

Pros

• Search volume, CPC and competition through a plain REST call, with one flat price for up to 50 keywords.
• No subscription or monthly minimum, so checking a shortlist of keywords costs cents.
• The same account adds Google Trends at $0.05 a request and AI visibility checks, and every tool also works over MCP in Claude, ChatGPT, Codex and Cursor.

Cons

• No organic keyword difficulty, SERP data or backlink index. Competition here is the paid-search figure.
• One average monthly volume per keyword rather than a month-by-month series. Use the Trends tool for seasonality.
• 50 keywords and one country per batch; ideas need a separate single-keyword call.

Here is the request, with your key in the CITE42_API_KEY environment variable:

curl --fail-with-body https://www.cite42.dev/api/v1/keywords/batch \
  -H "Authorization: Bearer $CITE42_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "seeds": ["seo mcp", "google trends mcp"],
    "country": "us",
    "language": "en"
  }'

Our October 5 batch checked 24 US keywords in one request and was billed $0.09. Two rows from that response:

{
  "results": [
    {
      "requestedKeyword": "seo mcp",
      "keyword": "seo mcp",
      "status": "exact",
      "volume": 90,
      "cpc": 17.930996,
      "competition": 0.53,
      "competitionLevel": "MEDIUM"
    },
    {
      "requestedKeyword": "google trends mcp",
      "keyword": "google trends mcp",
      "status": "exact",
      "volume": 50,
      "cpc": 3.813872,
      "competition": 0.13,
      "competitionLevel": "LOW"
    }
  ]
}

The response gives a monthly average without naming the reporting month, so we describe these as reported US monthly estimates retrieved on October 5. The full batch, a missing-data lookup and an ideas request are in the evidence file. For related keywords, call /api/v1/keywords with seed, country and ideas: true; the API documentation has both endpoints.

DataForSEO: the lowest cost per keyword at scale

DataForSEO's Keywords Data API returns Google Ads and Bing search volumes, CPC and competition, with a month-by-month history. One Google Ads task takes up to 1,000 keywords and costs $0.06 in the standard queue (results in about 45 minutes) or $0.09 in live mode. DataForSEO Labs adds keyword ideas, keyword difficulty and search intent from about $0.01 per request plus $0.0001 per returned keyword. Billing is pay-as-you-go with no subscription, and the pricing page sets a $50 minimum payment.

AI assistants recommend DataForSEO for this job more consistently than any other API we tracked. When we asked ChatGPT, Claude, Gemini, Perplexity and Google AI Overviews "What are the best keyword research APIs for developers?" on October 5, 2026, it appeared in all five answers.

Pros

• About $90 per million keywords in live mode, the lowest unit price here for large batches.
• Monthly volume history, plus SERP, backlink, on-page and AI data APIs under the same account and an official MCP server.

Cons

• $50 upfront before the first call.
• A task-based API with detailed raw JSON, and separate endpoints and prices to learn for each dataset.

Semrush and Ahrefs: keyword data from an SEO suite

Semrush's Standard API returns keyword overview, related keyword and question reports from Semrush's own database. API access is an add-on to the Business tier of its SEO Toolkit: your unit balance starts at zero, and you buy packages of 2, 5, 10 or 20 million API units. Semrush also runs an official MCP server, and its Semrush One Starter and Pro+ plans and SEO Classic Pro and Guru plans include 50,000 API units that work with it.

The Ahrefs API returns volume, keyword difficulty, clickstream data, parent topics and keyword ideas for a single keyword or a list. Access starts on the Lite plan. Each request uses API units from your plan's monthly allowance, with a 50-unit minimum per request, and the Ahrefs MCP server draws from the same allowance.

Pros

• Keyword difficulty and SERP data sit next to the backlink and competitor research you may already use.
• Both have official MCP servers for research inside an AI assistant.

Cons

• A suite subscription comes first, and Semrush's REST API also needs a separately bought unit package.
• Unit costs vary by report, which makes the cost per keyword harder to predict.

SE Ranking: volume and difficulty on pay-as-you-go credits

SE Ranking's Keyword Research API returns search volume, CPC, competition, keyword difficulty, search intent and a month-by-month trend, plus similar, related, long-tail and question keywords. One POST request takes up to 5,000 keywords, and SE Ranking puts its North American database at 1.2 billion keywords. API access runs on pay-as-you-go credits from $50 for 250,000, new users get 100,000 trial credits, and an MCP server connects the same data to Claude and other assistants.

Pros

• Difficulty, intent and monthly trend in the same response as volume.
• Pay-as-you-go credits without a suite subscription, and the same account covers backlinks, audits and AI visibility data.

Cons

• Each endpoint uses a different number of credits, so convert your workload into credits before comparing prices.

Google Ads API: Keyword Planner data from the source

The Google Ads API's historical metrics method returns average monthly searches, a monthly series for the past 12 months, competition level and index, and low and high bid estimates. A separate ideas method generates related keywords. It is the first-party source behind Keyword Planner numbers, and the API itself is free.

Access changed in 2026. Google sunset developer tokens on September 9, 2026 and moved sign-up to the Google Cloud Console. A new project starts with test access, which works only on test accounts. The next access level, Explorer, reaches production accounts but excludes the Keyword Planner services, so keyword research needs Basic access, which requires brand verification of your Cloud project and an application.

Pros

• First-party data with monthly history and location, language and network targeting.
• No per-call fee.

Cons

• OAuth setup and a Basic access approval before your first production keyword request.
• Close variants can come back grouped with your keyword, and you build storage, retries and quota handling (15,000 operations a day on Basic).

Keyword Tool: bulk volumes plus YouTube and Amazon ideas

Keyword Tool's API has separate endpoints for search volume and keyword suggestions. Google and Bing volumes come from Google Keyword Planner and Bing Keyword Planner, while YouTube, Amazon, eBay, TikTok and other platforms get estimated volumes. A volume request takes 1 to 1,000 keywords. Every Keyword Tool Pro plan includes the web app, API and MCP access; Starter costs $88 a month on monthly billing ($68 a month billed annually) with 50 requests and 50,000 keywords a day.

Pros

• One API for Google, Bing, YouTube, Amazon and other platforms.
• Up to 1,000 keywords per volume request, with MCP access included.

Cons

• A monthly subscription, with daily quotas shared between the web app, API and MCP.
• Volumes for platforms other than Google and Bing are estimates.

Serpstat: keyword difficulty beside domain data

Serpstat's API uses JSON-RPC 2.0 with a personal token and returns regional search volume, CPC, paid competition and a separate keyword difficulty score, alongside domain and backlink reports. Each returned row costs one API credit, with up to 60,000 rows per request. API access starts on the Team plan at $100 a month with monthly billing; the Individual plan has no API.

Pros

• Organic difficulty kept separate from paid competition.
• Keyword, domain and backlink data from one token.

Cons

• A monthly subscription before the first call.
• Every returned row uses a credit, including during development and testing.

What a 24-keyword check costs on each API

Take one realistic job: monthly volume and CPC for 24 keywords in the US.

• Cite42: one batch at $0.09. Our October 5 run of exactly this job was billed $0.09, and the $1.00 signup credit covers it.
• DataForSEO: one live task at $0.09, after the $50 minimum payment.
• SE Ranking: a small share of a $50 credit pack, or of the trial credits.
• Keyword Tool and Serpstat: included in a monthly plan from $88 or $100.
• Semrush and Ahrefs: included in a suite plan, plus Semrush's unit package for REST access.
• Google Ads API: free per call once Google approves Basic access.

At 10,000 keywords a month the order changes: DataForSEO handles that in 10 tasks of 1,000 keywords, while Cite42 needs 200 batches of 50. Cite42 is built for the shortlist-sized job, a few dozen keywords checked when you need them, with nothing to pay between checks.

Handle missing data and paid competition

Long, specific phrases often have no measured volume. Our check of "claude code keyword research with cite42" returned no_data, with volume, CPC and competition all null, plus broader alternatives such as "ai coding assistant" (18,100 searches). Show the requested keyword as having no data and list the alternatives separately, because the alternative's volume answers a different question. A null CPC works the same way: "ai visibility api" returned a volume of 10 with no CPC value, so its click cost is unknown rather than zero.

Competition in Cite42, Google Ads and DataForSEO's Keywords Data API measures advertisers bidding on the keyword. For how hard a keyword is to rank for organically, use a difficulty score from SE Ranking, Serpstat, Ahrefs, Semrush or DataForSEO Labs, or review the current search results yourself.

Frequently asked questions

What is the best keyword research API for developers?

It depends on volume and budget. DataForSEO has the lowest cost per keyword for large batches, SE Ranking and Serpstat add keyword difficulty, and Semrush or Ahrefs make sense if you already pay for those suites. Cite42 suits developers who want search volumes per call, with no subscription and a $25.00 minimum top-up.

Is there a keyword search volume API without a subscription?

Yes. Cite42 charges per successful call with no subscription: a batch of up to 50 keywords costs $0.09, and the prepaid balance never expires. DataForSEO and SE Ranking are also pay-as-you-go, with a $50 minimum payment at DataForSEO and credit packs from $50 at SE Ranking.

How can I get Google Keyword Planner data through an API?

The direct route is the Google Ads API, which since September 2026 is set up in the Google Cloud Console and needs Basic access for Keyword Planner services. DataForSEO's Keywords Data API returns Google Ads volumes through a simpler task-based API, and Keyword Tool sources its Google volumes from Keyword Planner too.

What is the cheapest SEO API for keyword data?

For a few dozen keywords, a per-call API keeps the bill smallest: Cite42 charges $0.09 for up to 50 keywords, funded from a $25.00 top-up or the $1.00 signup credit, and SE Ranking's trial credits cover a first test. For thousands of keywords a month, DataForSEO's $0.09 live task for up to 1,000 keywords costs less per keyword once you have paid its $50 minimum.

Can I use a keyword research API from Claude or ChatGPT?

Yes, through MCP. Cite42's hosted server at https://mcp.cite42.dev gives Claude, ChatGPT, Codex and Cursor the same keyword tools as its REST API, and DataForSEO, Semrush, Ahrefs, SE Ranking and Keyword Tool also run MCP servers. The SEO MCP server comparison covers the differences.

Check your own keyword list

Pick 10 to 50 keywords you're deciding between and run the batch request above. Create a free Cite42 account for $1.00 of starter credit, then get an API key from the dashboard. If you'd rather do the research in ChatGPT, the ChatGPT keyword research guide shows the setup, and the DataForSEO alternatives guide covers SERP and backlink APIs.