Choose a twin

Choose an implementation and an exact release for the vendor operations your app actually uses. Browse the catalog without signing in to a platform. Local execution needs the CLI and selected twin packages; a hosted World account is optional.

Start with your app's callsCopy Anchor Link

List the APIs your workflow needs: creating and retrieving a customer, receiving a webhook, or searching and extracting a page. Review what volter world init detects from dependencies and env names. Include the vendors you deliberately want to substitute.

Detection identifies vendors; it does not establish support for every operation. Missing operations and unselected vendors need an explicit decision, not a handler that fabricates a successful stored write.

Compare releasesCopy Anchor Link

Search the catalog by vendor, workflow or publisher. A vendor page opens its selected default when one exists; otherwise, choose an implementation and version from the recorded releases. Use Overview for workflow documentation, Setup for the exact installation and World configuration, Versions to compare releases and implementations, and Evidence for the assessment details. The version selector opens an exact release. Read:

• Declared HTTP surface: measured HTTP operations served and gaps. Read the README for exact operations, SDK expectations, default data and limitations.
• Exercised HTTP operation coverage: declared HTTP operations the recorded journeys called, with their denominator. This is different from supported HTTP surface. Separate command tables and other protocols are outside these counts; check the release’s README for those workflows.
• Replay: whether those journeys gave equal results from their recorded starting conditions.
• Chromium journey replay: the HTTP operations exercised at each request’s origin, with the journey’s authored headers. This does not establish application-origin CORS, native cookie handling, your app’s UI or every vendor screen. Read the report’s stated scope.
• Publisher and admission: who supplies the implementation and how it was admitted. Trusted publisher status describes admission, not complete fidelity.

“Not measured” means no measurement is available. A percentage is useful only with its scope. Choose for your app's operations, then exercise them through your real SDK. The coverage reference owns these distinctions.

Different SDKs and languagesCopy Anchor Link

Node applications run through the World's injected environment and routing. For Python or a native CLI, use the client's supported proxy, CA or endpoint configuration in route a client through the World. A twin's API support and a client's ability to reach it are separate requirements. If your app needs a database or background services, run a full stack keeps them in the same workflow.

Read a published snapshot from the CLICopy Anchor Link

The website displays a pinned catalog snapshot. You can inspect a specific published snapshot yourself. Use Node 22.6 or newer and npm; registry access is needed for installation. In an empty directory, save package.json:

{
  "name": "catalog-choice",
  "private": true,
  "devDependencies": { "@volter/twin-catalog": "0.2.3" }
}

npm install
npx twin-catalog browse --root ./node_modules/@volter/twin-catalog --vendor tavily
npx twin-catalog defaults

This reads data; it does not run twins or create a World. The output includes package identities, versions, selection state and available evidence. The website may use a different snapshot; compare its snapshot version before expecting the same choices.

Choose one implementationCopy Anchor Link

The recommended default is a catalog choice. Multiple implementations without a recommendation require an explicit choice. Publishers' version numbers do not rank implementations: another publisher's 2.0.0 is not necessarily better than 1.0.0.

Copy a selectable release's install command. Install exactly the package and version it names, and keep the lockfile. A vendor id such as tavily and a package such as @volter/twin-tavily are separate identities; another publisher can use a different npm name.

Use a catalog twin shows the complete next steps: run the release with the real SDK, supply synthetic starting data, and check results.

When there is no suitable releaseCopy Anchor Link

Pending, rejected and revoked versions remain visible as history, without being offered as installation choices. An admitted release can still have gaps, and its assessment may not exercise your operation. Read its README and reproduce your call before depending on it; report the failing operation and selected version to its publisher.

If the catalog has no implementation for your vendor, keep that gap explicit. You can use a different workflow whose calls are covered, continue with the vendor's own test environment under a separate deliberate setup, or request an implementation from a publisher. Excluding a vendor from a World does not grant it network access or make it covered.

Existing World pins do not automatically change with catalog recommendations or revocations. Update a twin explains deliberate updates. Creating an implementation is a separate task in the catalog's publisher guide.