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APIs · head to head

Asyncapi vs Basis Theory

Asyncapi logo

Asyncapi

APIs

Specification and tools for defining asynchronous APIs

From
Free
Rated
-
Full reviewWebsite
Basis Theory logo

Basis Theory

APIs

Developer tokenisation platform that holds card and sensitive data inside a PCI Level 1 environment you do not operate

From
$995/month
Rated
-
Full reviewWebsite

The short version

  • Only Asyncapi has a free tier, so it costs nothing to try first.
  • Each has a real cost: Asyncapi complex to implement and debug asynchronous operations due to their non-linear and concurrent nature; Basis Theory the Starter plan is 995 US dollars a month before any volume, which is a real floor for an early stage company and puts the product out of reach of teams tokenising a few thousand records.
  • They diverge on capability: Asyncapi covers API Specification, Basis Theory covers Tokenisation API.
  • Prices and features above were last checked on 31 August 2026.

Where they differ

Only the attributes on which Asyncapi and Basis Theory actually diverge.

Attributes where Asyncapi and Basis Theory differ
AttributeAsyncapiBasis Theory
Starting priceFree$995/month
Pricing modelopen-sourcePer month by token volume
Free tierYesNo
PlatformsWeb, CLI, IDE ExtensionsWeb, iOS, Android, Linux
Founded2019Unknown

Identical on both: user rating (Not yet rated), category (APIs).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Asyncapi

  • API Specification
  • Code generation
  • Documentation
  • Multiple messaging protocols
  • Code generators
  • Specification support
  • Tools support
  • CLI support

Only in Basis Theory

  • Tokenisation API
  • Hosted elements
  • Outbound proxy
  • PCI attestation of compliance
  • Processor portability
  • Reactors
  • Access controls and audit
  • PII and PHI options

What people use each for

The jobs each tool is most often brought in to do.

Asyncapi

  • API Developmentnot Basis Theory
  • API Gatewaynot Basis Theory
  • API Testingnot Basis Theory
  • API Documentationnot Basis Theory
  • Microservicesnot Basis Theory

Basis Theory

  • A payments company that wants card on file without bringing its own infrastructure into PCI scope and paying for the assessment that followsnot Asyncapi
  • A merchant locked into a processor by that processor vault that wants to hold its own tokens and route to more than one acquirernot Asyncapi
  • A fintech collecting bank account and identity data that needs it isolated from its application database before an enterprise security reviewnot Asyncapi
  • A team that needs to send stored card data to a third party for a one-off integration without that data traversing its own serversnot Asyncapi

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Asyncapi

  • Complex to implement and debug asynchronous operations due to their non-linear and concurrent nature
  • Keeping AsyncAPI documents up to date is challenging as systems evolve
  • Tracing and debugging asynchronous operations is more difficult than synchronous request-response patterns

Basis Theory

  • The Starter plan is 995 US dollars a month before any volume, which is a real floor for an early stage company and puts the product out of reach of teams tokenising a few thousand records.
  • Starter is limited to the US region, so a company with European data residency requirements is pushed into a quoted Scale or Enterprise agreement immediately.
  • Log retention on Starter is 24 hours, which is well below what most security teams expect for a system holding cardholder data and forces an upgrade for reasons unrelated to volume.
  • Migrating away means moving card data out of the vault, which requires processor and assessor involvement and is slow, so the portability argument that attracts buyers cuts against them at exit.
  • An attestation of compliance covers the vendor environment, not your assessment; your assessor still decides what is in scope, and buyers occasionally discover their integration pattern pulled systems back into scope anyway.

Pricing, plan by plan

Asyncapi

Free
  • Open SourceFree
    • AsyncAPI specification
    • Tools
    • Community support

Basis Theory

$995/month
  • Starter$995/month
    • 20,000 tokens included
    • Production PCI Level 1 environment
    • US region only
  • Scale$undefined/month
    • Quoted
    • Higher token volumes
    • Additional regions
  • Enterprise$undefined/month
    • Quoted
    • Additional compliance options for PII and PHI
    • Responses for 95 percent of PCI SAQ D

Which should you pick?

Choose Asyncapi if

  • You need api specification.
  • You want to start without paying.
  • You work on Web, CLI, IDE Extensions.
  • You also want code generation.
Asyncapi review

Choose Basis Theory if

  • You need tokenisation api.
  • You work on Web, iOS, Android, Linux.
  • You also want hosted elements.
Basis Theory review

Questions people ask

Is Asyncapi or Basis Theory better?
Neither clearly leads. Asyncapi starts at Free and Basis Theory at $995/month, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Asyncapi or Basis Theory?
Asyncapi has a free tier; the other does not. Paid plans start at Free for Asyncapi and $995/month for Basis Theory.
Does Asyncapi or Basis Theory run on more platforms?
Asyncapi runs on Web, CLI, IDE Extensions. Basis Theory runs on Web, iOS, Android, Linux.
Can I use Asyncapi for free?
Yes. Asyncapi has a free tier, so you can try it without paying. Basis Theory starts at $995/month.
What is Asyncapi best used for?
Asyncapi is most often used for api development, api gateway, api testing, api documentation. Of those, api development and api gateway are not what Basis Theory is typically brought in for.
What can Asyncapi do that Basis Theory cannot?
Asyncapi covers API Specification, Code generation, Documentation, Multiple messaging protocols. Basis Theory covers Tokenisation API, Hosted elements, Outbound proxy, PCI attestation of compliance.

Answered from the vendors’ own pages

Asyncapi: What is AsyncAPI used for?

AsyncAPI is an open-source specification for defining and documenting asynchronous APIs, message-driven systems, and event-driven architectures. It serves the same purpose for async APIs as OpenAPI does for REST APIs, providing standardized documentation, code generation, and tooling.

Source
Basis Theory: Does this make us PCI compliant?

It removes cardholder data from your systems and gives you an AOC plus documented responses for most of a SAQ D. Your assessor still determines your scope, and a careless integration can pull systems back in.

Asyncapi: Is AsyncAPI free to use?

Yes, AsyncAPI is completely free and open-source. It is hosted by the Linux Foundation and supported by community contributions and sponsorships from companies like Postman, IBM, IQVIA Technology, and Solace.

Source
Basis Theory: What does it cost to start?

995 US dollars a month on Starter, including 20,000 tokens, a production PCI Level 1 environment and US hosting. Higher tiers are quoted.

Asyncapi: What protocols and technologies does AsyncAPI support?

AsyncAPI supports multiple protocols and technologies including Kafka, RabbitMQ, MQTT, Socket.IO, AWS EventBridge, and others. It provides language support for JavaScript/TypeScript, Python, Java, Go, C#/.NET, Kotlin, and PHP.

Source
Basis Theory: Can we switch payment processors without re-collecting cards?

Yes, that is the main non-compliance reason to buy it. You hold the tokens and detokenise into whichever processor you route to.

Asyncapi: Does AsyncAPI have IDE support?

Yes, AsyncAPI has IDE extensions available for VSCode and IntelliJ, along with CLI utilities and GitHub Actions integration for developers.

Source
Basis Theory: Is data stored outside the United States?

Not on Starter, which is US only. Other regions require a Scale or Enterprise agreement.

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