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[!WARNING]

The Optimization SDK Suite is pre-release (alpha). Breaking changes can be published at any time.

The Optimization Core SDK owns the platform-agnostic optimization state machine, event builders, queues, resolvers, and interceptors used by the application-facing SDKs. Web, React Web, Node, React Native, and native bridge layers build on this package.

We recommend starting application code with a platform SDK rather than Core directly. Use this README when building or maintaining SDK layers, and use Choosing the right SDK when deciding which application-facing package belongs in an integration. Generated reference documentation remains the source of truth for exported API signatures.

• Getting started
• When to use this package
• Core variants
  • Stateful Core
  • Stateless Core
• Common configuration
• Package surface
• Preview support
• Related

Getting started

Install using an NPM-compatible package manager, pnpm for example:

pnpm install @contentful/optimization-core

Choose the stateful or stateless Core class based on the runtime layer you are building:

import { CoreStateful, CoreStateless } from '@contentful/optimization-core'

const statefulOptimization = new CoreStateful({ clientId: 'your-client-id' })
const statelessOptimization = new CoreStateless({ clientId: 'your-client-id' })

Stateful runtimes own durable in-process SDK state. Stateless runtimes bind request-scoped consent, profile state, event context, and Experience API options before calling event methods:

const requestOptimization = statelessOptimization.forRequest({
  consent: true,
  eventContext: { locale: 'en-US' },
  experienceOptions: { locale: 'de-DE', preflight: false },
  profile: { id: 'profile-id' },
})

await requestOptimization.page()

When to use this package

Use @contentful/optimization-core when you are building or maintaining an SDK layer that needs the shared optimization state machine, event builders, queueing, resolvers, or interceptors. Most application code uses a platform SDK such as Web, React Web, Node, or React Native instead of depending on Core directly.

Core variants

Stateful Core

CoreStateful is the basis for SDKs that run in stateful JavaScript runtimes such as browsers, mobile JavaScript containers, and native bridge runtimes. It maintains consent, profile, selected optimization, flag, event-stream, blocked-event, and preview-panel state as read-only observables.

[!IMPORTANT]

CoreStateful uses module-global state by design. Initialize exactly one stateful instance per JavaScript runtime and reuse it.

Stateless Core

CoreStateless is the basis for SDKs that run in stateless environments such as Node servers and server-side functions. It does not store consent or profile state between requests. Consumers call forRequest() to create a request-bound event client with the consent, profile, event context, and Experience options for that one incoming request.

Common configuration

Shared Core configuration:

| Option | Required? | Default | Description | | -------------- | --------- | --------------------- | ----------------------------------------------------------- | | clientId | Yes | N/A | Shared API key for Experience API and Insights API requests | | environment | No | 'main' | Contentful environment identifier | | api | No | See API options below | Experience API and Insights API endpoint options | | eventBuilder | No | SDK-layer defaults | Event metadata overrides for platform SDK authors | | fetchOptions | No | SDK defaults | Fetch timeout and retry behavior | | logLevel | No | 'error' | Minimum log level for the default console sink |

Consent and event configuration:

| Option | Required? | Default | Description | | ------------------- | --------- | ----------- | ------------------------------------------------------------ | | allowedEventTypes | No | [] | Event types allowed before consent is explicitly set | | onEventBlocked | No | undefined | Callback invoked when consent or guard logic blocks an event |

Core itself fails closed before consent. Platform SDKs set runtime-specific defaults for the event types that make sense in that runtime, such as browser identify/page, server identify/page, and mobile identify/screen.

Stateful-only configuration:

| Option | Required? | Default | Description | | ---------------- | --------- | ------------ | --------------------------------------------------------------------------------- | | defaults | No | undefined | Initial state, commonly including consent, persistence consent, or profile values | | getAnonymousId | No | undefined | Function used to provide an anonymous ID from application-owned identity state | | queuePolicy | No | SDK defaults | Flush retry behavior and offline queue bounds |

Persistence consent controls durable profile-continuity storage for SDKs with runtime storage: profile, anonymous ID, changes, and selected optimization caches. Event consent, stored consent decisions, and debug state are tracked separately.

Common api options:

| Option | Applies to | Default | Description | | ------------------- | ---------- | ------------------------------------------ | ----------------------------------------------- | | experienceBaseUrl | All | 'https://experience.ninetailed.co/' | Base URL for the Experience API | | insightsBaseUrl | All | 'https://ingest.insights.ninetailed.co/' | Base URL for the Insights API | | enabledFeatures | All | ['ip-enrichment', 'location'] | Experience API features for each request | | beaconHandler | Stateful | undefined | Custom handler for enqueueing Insights batches | | ip | Stateful | undefined | IP address override for Experience API analysis | | locale | Stateful | API default | Locale query parameter for localized responses | | plainText | Stateful | false | Sends performance-critical endpoints as text | | preflight | Stateful | false | Aggregates a profile state without storing it |

In stateless environments, pass ip, locale, plainText, and preflight as experienceOptions when creating the request-bound client instead of constructor config.

Core-backed stateful SDKs can accept contentfulLocales, an initial app/content locale, and runtime setLocale(locale) calls. They expose the resolved Contentful locale through the live locale getter and states.locale observable. The stateful api.locale config remains an explicit Experience API override; otherwise stateful SDK layers use the current resolved Contentful locale for Experience API localization. Stateless server SDKs should pass the request-scoped Contentful locale as the per-call { locale } option.

contentfulLocales.default and optional contentfulLocales.supported values should use the locale codes configured in Contentful locale settings or returned by the CMA locale list. The resolved value remains the configured Contentful locale code because that code is the API identifier used for CDA requests. For configuration cases, matching rules, and runtime-specific locale sources, see Locale handling in the Optimization SDK Suite.

Common fetchOptions are fetchMethod, requestTimeout, retries, intervalTimeout, onFailedAttempt, and onRequestTimeout. Default retries intentionally apply only to HTTP 503 responses.

For every option, callback payload, and exported type, use the generated Core SDK reference.

Package surface

Core exposes reusable primitives for SDK layers:

| Surface | Purpose | | ------------------------------- | ---------------------------------------------------------------------- | | CoreStateful | Stateful optimization runtime for browser, mobile, and bridge SDKs | | CoreStateless | Stateless optimization runtime for server SDKs | | Event methods | identify, page, screen, track, trackView, trackClick, etc. | | Resolution helpers | resolveOptimizedEntry, getMergeTagValue, and getFlag | | states | Stateful observable state streams | | Interceptors | First-party hooks for event and state lifecycle customization | | Queue policy and fetch helpers | Shared retry, flush, timeout, and offline buffering behavior | | Signal and observable utilities | Lightweight reactive primitives used internally by stateful SDK layers |

Resolution helpers expect Contentful entries fetched by the app layer with one CDA locale. Use the resolved SDK locale, withOptimizationLocale(contentfulClient), or the Node SDK's resolveRequestLocale() result before resolving entries. Do not pass all-locale CDA responses from withAllLocales or locale=*; optimization fields such as fields.nt_experiences and fields.nt_variants must be direct single-locale field values. See Entry personalization and variant resolution for the entry contract and Locale handling in the Optimization SDK Suite for the broader locale model.

The generated reference owns method arguments, return types, callback payload shapes, and inherited members. Keep this README focused on package role and maintainer orientation.

Preview support

Preview-panel helpers live under the internal preview-support entry. They are used by first-party preview surfaces to register preview state bridges, apply optimization overrides, and map Contentful entries for local authoring workflows.

Application code must not use preview support directly unless it is building a first-party preview surface.

Related

• Choosing the right SDK - package selection guidance for application integrations
• Core SDK generated reference - exported API reference
• Optimization Web SDK - browser SDK built on CoreStateful
• Optimization Node SDK - server SDK built on CoreStateless
• Optimization React Native SDK - mobile SDK built on CoreStateful
• Core preview support - internal preview helper entry