These two come up together because both relate to API contract drift. They solve different problems at different scales. Live Types is not a Pact alternative for consumer-driven contract testing, and it doesn't do what Pact does. This page is about which one fits your situation.
What Pact is
Pact is a consumer-driven contract testing framework. The consumer of an API (a frontend, or a service that calls another service) writes tests against a mock provider that describe what it expects back: which fields, which types, which values matter. Running those tests produces a "pact" file, a formal record of the consumer's expectations.
The contract gets published, usually to a Pact Broker. The provider's CI pipeline then runs a verification step that replays the contract against the real provider. If the provider no longer satisfies a consumer's contract, verification fails in CI and the breaking change never reaches production.
So Pact gives you automated contract testing that runs on every build, with a broker to track contract versions across many consumers and providers. Both sides have to take part. The consumer writes and publishes contracts, and the provider runs verification in its own CI. It's a mature, well-established setup for organizations that can work that way.
What Live Types is
Live Types is a browser tool, and it has none of that infrastructure. No consumer-written contract, no provider-side verification, no broker, and no CI integration in its current form. That's deliberate: everything runs in your browser, so there's no server to host contracts or run checks.
You paste one or more real response samples from an API and get a merged TypeScript type and Zod schema inferred from them. You can save that inferred shape as a snapshot. Later you paste a fresh sample and diff it against the snapshot to see what changed: a field added, removed, or switched in type or optionality.
It's useful, but it's a manual check that you start. You have to remember to paste and diff again. It doesn't run in CI, doesn't block deploys, and doesn't need anything from the API provider.
The differences side by side
| Pact | Live Types | |
|---|---|---|
| Enforced automatically in CI | Yes, provider verification fails the build | No, you re-check by hand |
| Requires provider's cooperation | Yes, the provider runs verification against the contract | No, it works against any API you can call, including third-party ones you don't control |
| Setup cost | Significant: broker infrastructure, CI wiring on both sides | None: paste a sample in a browser tab |
| Contract origin | Consumer-authored expectations | Inferred from observed responses |
| Best fit | Multiple services you control, wanting CI-enforced guarantees | A third-party or internal API you consume but don't own, when you want a quick drift check |
How each one catches drift
With Pact, the consumer's tests already state the expectation, something like "a GET to /users/:id returns an object with a string id and a string email." If the provider's next deploy drops email, the provider's CI runs verification against the published contract, verification fails, and the deploy is blocked, just as any failing test would block a merge. Nobody has to remember to check. The pipeline does it.
With Live Types there's no test suite and no CI step. You pasted a response from the same endpoint weeks ago and saved it as a snapshot. If you paste a fresh sample later, because something looked off or because you check now and then, the diff shows something like:
- email removed
It's the same fact Pact would have caught, but nothing made you look. If you never paste another sample, this tool never notices the drift. There's no pipeline gate because there's no pipeline integration. That's why it isn't pitched as a Pact alternative. Pact is valuable because it doesn't depend on someone remembering.
Team structure decides which one applies
Pact's consumer-driven model assumes you can get the provider team to run verification in their CI. Inside one organization, with both teams willing, that's simple. When the provider is a third-party API you only know through an API key, it's much harder and often impossible. Live Types never asks the provider for anything. It only looks at responses you've already received. That's the main reason the two don't substitute for each other: they're built for different relationships with whoever runs the other end of the API.
Signs you've outgrown Live Types
These are the situations where a manual browser check stops being enough and CI-enforced contract testing is worth setting up:
- More than one consumer depends on the same provider. Once two or more services use the same API and each cares about different fields or edge cases, no one person can remember to re-check all of those expectations by hand. Pact handles this: each consumer publishes its own contract and the provider verifies against all of them. Pasting samples into a browser tool, per consumer and per provider, whenever someone remembers, doesn't.
- A broken contract has to block the deploy. If the requirement is that the provider's CI fails before a breaking change reaches production, you need CI integration. A manual browser check can't block anyone's deploy, however careful the people doing it are.
- You're coordinating contract changes across many services. When tracking which consumer expects which version of which provider's contract becomes a problem in itself (enough services that nobody can hold it all in their head), that's the job a Pact Broker does. Live Types has no concept of multiple consumers or contract versions.
- You control the provider and can get its team to add a CI step. Pact only works when the provider can run verification. If that's possible in your organization (same company, teams that cooperate), the CI enforcement is available to you. Live Types is for when it isn't: a third-party API, a team you can't influence, or a provider that won't add contract-testing infrastructure on your behalf.
These describe where Live Types' scope ends. A browser tool that infers shapes from pasted samples won't turn into CI-enforced, multi-consumer contract testing without becoming a much bigger and different product.
When to use each
If you control both consumer and provider and want breaking changes caught automatically before they ship, use Pact. Live Types isn't competing with that. Setting up Pact's broker and CI verification takes work, and what you get for it is something Live Types can't give you: a failing build instead of a surprise in production.
Live Types covers a narrower and more common everyday case. You're calling an API, often one you don't control and couldn't ask to run Pact verification anyway. You want to know what shape it returns now, and later whether that shape has changed. There's no CI setup, no coordination with the provider, and no broker. You give up continuous automated enforcement, and in return you get zero setup and a tool that works on APIs you have no control over.