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SDK Types

FlagSync offers two SDK types for different environments:

Client-Side

For single-user contexts (e.g., web/mobile apps).

Server-Side

For multi-user contexts (e.g., web servers, APIs).

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Using Both SDK Types for SSR Apps

SSR web apps often benefit from using both SDKs for seamless feature management. Server-side SDKs enable flag evaluation for redirects (e.g., rerouting if a feature is off) and tracking purchases, while passing flags to the UI to avoid client-side SDK calls. Meanwhile, client-side SDKs track events like page_load_time or button clicks, ensuring comprehensive data collection.
This combination is not uncommon and offers server-side control and client-side tracking flexibility.

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Key Differences

Initialization

Client-side SDKs require a user context at initialization.


Server-side SDKs initialize without one.

Flag Evaluation

Client-side SDKs evaluate on FlagSync’s servers and send key-value pairs for the user to the client.


Server-side SDKs fetch full rulesets from FlagSync and evaluate locally at runtime.

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Next Steps

Explore more about SDKs and flag evaluation: