Westlaw API: What Exists, Who Can Use It and What It Covers

Short answer: Yes. Thomson Reuters, the company that owns Westlaw, offers APIs that carry some Westlaw content, such as litigation analytics and legislation data. (An API, short for application programming interface, is a way for one program to ask another for data.) It lists them on a developer portal, and its own announcement to developers says the way to get keys is to "Connect with sales for a subscription." The public terms we could read also bar training AI on API content and building a product on it for other people, so the contract you sign decides what you may do.

TL;DR

• Westlaw APIs exist, and access is by contract. Thomson Reuters points developers to its sales team for keys. We found no self-serve sign-up that issues them.
• The developer portal is a general portal. Much of it serves tax, trade, risk and fraud customers. Only some APIs relate to Westlaw or legal content.
• The Westlaw-related APIs Thomson Reuters names include Westlaw US Litigation Analytics and a Westlaw US Legislation API. The full catalog needs a browser, and some pages need a login.
• Its public terms limit AI and resale. One clause bars training AI on API content. Another bars using the content as a component of a product for third parties.
• Pick by what you need. For content only Westlaw has, a contract with Thomson Reuters is the route. For the text of statutes, regulations, court rules or agency guidance by citation, a primary law data API may fit better.

What people mean by "Westlaw API"

Westlaw is the legal research service sold by Thomson Reuters. People who search for a "Westlaw API" usually want one of two things.

The first is Westlaw's own editorial work inside their software: citation checking, analytics on judges and lawyers, practice guides, court dockets (the list of filings in a case). That content belongs to Thomson Reuters, so Thomson Reuters is the source.

The second is the text of the law inside an app: a statute (a law passed by a legislature), a regulation (a rule written by a government agency), or a court rule. Governments publish that text, and several providers serve it. For this need, a Westlaw contract may be more than you need.

A short history of Westlaw

Westlaw is older than most of the software that now plugs into it, and the history explains why access works the way it does.

Thomson Reuters's 150th anniversary release tells the start of it. In 1872 John B. West opened a small shop in St. Paul, Minnesota, called John B. West Publisher and Book Seller. Minnesota had been a state for only 14 years, and the release says it "could take months or years" for court decisions to travel from the eastern courts to its law offices. West started collecting decisions himself. A weekly publication of excerpts from Minnesota courts, The Syllabi, grew into the North Western Reporter, which added editorial work by attorneys. The National Reporter System followed.

The next idea was a filing system for the law. The Key Number System sorts points of law into a numbered outline. Similar holdings from different courts and states end up under the same heading. A law library guide from the University of North Carolina dates it to 1908. The same guide has the rest of the timeline. Westlaw launched in 1975. Thomson Corporation bought West Publishing in 1996. Westlaw.com opened to ordinary web browsers in 1998. In 2008, according to the company's own history page, the Thomson Corporation and Reuters Group combined to form Thomson Reuters.

Why does that matter if you want an API? The company describes its value as the editing layered on top of the law. Paul Fischer, president of its Legal Professionals business at the time, put it this way in the 2022 release: "Our exclusive attorney-authored content and our living taxonomy of the law provide the deep data needed by artificial intelligence technology to drive our next-generation legal research products."

The law treats that layer differently from the underlying text. In its 2020 decision in Georgia v. Public.Resource.Org, the US Supreme Court walked through the 19th-century rules. Court opinions themselves belong to no reporter (Wheaton v. Peters, 1834). But a private reporter who writes his own headnotes, summaries and tables of contents can own those (Callaghan v. Myers, 1888). The Court's summary is on Cornell's Legal Information Institute. So a Westlaw contract buys access to editorial work that belongs to someone. The text of a statute or regulation is a different thing. A legislature or an agency wrote it.

What Thomson Reuters offers developers

Thomson Reuters launched a global developer portal on April 10, 2024. Its press release says the portal offers "access to over 100 APIs" for "tax, legal, risk and fraud professionals," with "content from Checkpoint and Westlaw, as well as technology powering ONESOURCE and Thomson Reuters AI capabilities." It names two example APIs: "Checkpoint Search and Westlaw US Litigation Analytics."

Checkpoint is a tax research product. ONESOURCE is tax software. So the portal is a general one, and much of it has nothing to do with legal research.

When we checked on 2026-10-05, these were the APIs that Thomson Reuters, or the trade press reporting on it, named in public:

Other directories list more Westlaw APIs, such as dockets and citation data. We left those out because we could not find them on a Thomson Reuters page, so the full catalog is longer than this table.

Thomson Reuters's "The power of APIs" page has a "Legal Data APIs" entry. When we checked, its link (legal.thomsonreuters.com/en/products/legal-api) forwarded to the main Westlaw product page, whose text describes no API. The developer portal is where API details live.

In their words

At the portal launch, Thomson Reuters framed it as a change of posture. Kirat Sekhon, then its interim head of engineering, said in the April 2024 release: "Our new Developer Portal represents a fundamental shift in how we empower our customers and partners." The same release says the company's APIs "currently handle over 1.5 billion calls monthly." Legal tech journalist Bob Ambrogi covered the launch on LawNext and noted that the portal lets developers search by industry, by product such as HighQ, Legal Tracker or Westlaw, or by capability, and groups APIs by use case.

Keep that in mind when you see "100 APIs" in a headline. The launch release itself lists tax products next to Westlaw ones, so only a slice of the catalog is about legal research.

How you get access

The April 2024 announcement on Thomson Reuters's developer community answers this directly. Its FAQ asks "How do you I get API keys?" and replies: "Connect with sales for a subscription, and our will assist with the rest." (The "our" is in the original.) It gives one sales link for "Legal, Risk & Fraud" and another for tax and trade. The same post says keys are managed in an "App Management" section after you log in, and that new users can sign up for the community.

So registration lets you look around, and keys come from a subscription arranged with sales. A question on the same forum shows how that feels. A developer wanted to evaluate the Westlaw US Legislation API, found that the portal's test requests returned a 401 error (the standard code for "you are not signed in with a valid key"), and asked whether they needed a Westlaw subscription and an API subscription just to evaluate it. A Thomson Reuters staff member replied that the question had been passed to the developer team and that someone should reach out. The next step, in other words, is a conversation.

What is published about documentation and sign-in

Thomson Reuters describes the portal as the place for "tools, documentation, sample code, learning materials, and discussions." The forum thread shows that at least one Westlaw API has a reference page with a built-in test tool.

We could not read it. The portal is a JavaScript application, and its catalog pages gave our tools an empty shell. So we found no readable page that states the sign-in method, rate limits or response formats for a Westlaw API, and we will not guess. A person with a browser will see more than we could.

What the terms say about AI and building products

The portal's terms of use are public. We read them on 2026-10-05. Two clauses matter to anyone building with AI or building a product. On AI, you agree:

"Not to use API, Thomson Reuters Content or any other content or information obtained from our API, Website or Services to train any artificial intelligence ("AI") or machine learning algorithms"

On products, in the copyright section:

"Thomson Reuters Content, Services, and APIs may not be used as a component of any other product, service or material or provided on a white-labeled/re-branded basis, or otherwise, for the benefit of any third party. You may not build a business using the Thomson Reuters Content, whether or not for profit."

Two cautions apply, in fairness to Thomson Reuters.

First, these are the portal's terms. They also say: "The parties shall enter into separate additional terms for the use and access of APIs, and these Terms shall not replace or modify the terms contained in any subscription or other API agreement you have with Thomson Reuters." The signed API agreement governs your use.

Second, Thomson Reuters publishes Application Programming Interface Product Specific Terms (version 1.1, May 2023, hosted on its UK legal site). They let you use API content "into only (i) Your Applications for your internal business purposes, or (ii) if you are in the business of providing legal advice, dashboards you create at no cost for your individual clients, and provided such dashboards are not publicly available." They bar using the API or its data "to adapt, train, or develop any artificial intelligence (AI), machine learning algorithms, or any other software systems or tools." For Practical Law, only limited metadata may come through the API. When the agreement ends, you delete the data within thirty days. We cannot tell whether your contract would use that version, so ask for the terms that apply to the specific API.

Thomson Reuters draws a similar line for its AI assistant. The help page for its CoCounsel connector says the General Terms bar using Thomson Reuters content with another "Professional AI Tool," including through an MCP (a standard way for AI tools to connect to outside data). We cover that in our guide to whether Lexis+ AI, CoCounsel and Westlaw's AI products have an API.

Our reading: the public terms appear to fit an internal tool at a company that is already a Thomson Reuters customer. They do not appear to cover a product you sell to others, or an AI system built on the content, unless your contract says so.

What is publicly stated about coverage

Not much, at the level an engineer needs. The Westlaw Advantage product page speaks in broad terms, such as "Hundreds of attorney-editors maintain legal content." On the Westlaw pages we read, we found no document counts, jurisdiction lists or update schedules for a Westlaw API. We found no price either. The community announcement sends you to sales instead. Ask for coverage in writing, endpoint by endpoint, because an API may return a smaller slice than the website shows.

Which route fits

A contract with Thomson Reuters is the route when you need content that only Westlaw has, such as its analytics or Practical Law material. It also fits when you are a customer building an internal tool. If you want to show the content to your own customers, or use it with AI, negotiate that into the contract before you build.

A primary law data API fits when you need the text of the law itself, found by citation, and you want to start without a sales cycle. That means statutes, regulations, court rules and agency guidance. Vaquill AI is one such provider: its API is built for US statutes, regulations, court rules, agency guidance and other primary law, retrieved by citation. For a map of the options, see our guide to the best legal data APIs for developers and the overview of US law data. Some teams use both: Westlaw for the editorial layer, and a primary law API for the raw text.

What to check before you choose

If you are considering a Thomson Reuters contract, ask:

1. Which APIs cover my need, by name, and what does each one return?
2. Do I need a Westlaw subscription as well as the API subscription?
3. May my product show this content to customers, or only to my own staff?
4. Do the terms allow use with AI, such as search or summaries over the content, and in which products?
5. What are the rate limits, the sandbox rules and the support terms?
6. What must I delete when the contract ends, and by when?

If you are considering a primary law data API, use our ten questions to ask a legal data vendor. In short: where does each section come from, is it the official text, how current is it, what does the licence allow for my use, and what happens to me if the vendor changes. Our guide to what legal data is covers the vocabulary. For the Lexis side of the same decision, see LexisNexis and Westlaw API alternatives for developers.

Try it: resolve a citation

The quickest check of a primary law API is to hand it a citation and see if it returns the exact section. This example calls the citation resolve endpoint of the Vaquill AI API.

curl -G "https://api.vaquill.ai/api/v1/us/statutes/resolve" \
  --data-urlencode "cite=42 U.S.C. 1983" \
  -H "Authorization: Bearer $VAQUILL_API_KEY"

The cite parameter takes a Bluebook citation. When we ran it on 2026-10-05, the response had resolved: true, the title "Civil action for deprivation of rights," a stable actId, a currentThrough date, and a link to the official text on uscode.house.gov. A citation that does not match returns resolved: false, which is the answer you want when you are checking a citation an AI wrote.

FAQ

Does Westlaw have an API?

Yes, through Thomson Reuters's developer portal and by contract. It names Westlaw US Litigation Analytics as one example, and a Westlaw US Legislation API has a reference page. Its announcement tells developers to connect with sales to get keys.

Is there a free or self-serve Westlaw API?

We found none. Registering lets you explore, but the announcement says keys come through a subscription arranged with sales.

Can I use the Westlaw API to train or power an AI tool?

The public terms bar using API content "to train any artificial intelligence" or machine learning algorithms, and the API-specific terms say the same. Other AI uses are a question for your contract. Thomson Reuters's connector terms also bar passing its content to another professional AI tool.

Can I build a product on Westlaw data?

The portal terms say the content may not be "used as a component of any other product, service or material" for the benefit of a third party. A separate API agreement governs your actual use, so ask what it allows.

Are all the APIs on the Thomson Reuters developer portal about Westlaw?

No. The portal serves tax, trade, risk and fraud customers as well. The launch release names tax products (Checkpoint, ONESOURCE) next to Westlaw ones.

What does a Westlaw API cost, and what does it cover?

Thomson Reuters states no price and no coverage counts on the pages we could read. Its materials send you to sales, so expect a quote. Ask for the coverage of each endpoint in writing before you sign.

What if I only need the text of statutes and regulations?

A primary law data API can return statutes, regulations, court rules and agency guidance by citation without a Westlaw contract. Check the licence for your use, how current each section is, and where the official source link points.

For the data behind a guide like this one, see the US primary law API.

Priyansh Khodiyar

Co-Founder & CTO

Priyansh leads engineering and AI at Vaquill AI: the pipelines that pull statutes, regulations and court rules from every US jurisdiction's official publisher, and the REST API, MCP server and open dataset that serve them.