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The Chrome storage API offers several areas. The two you use most are storage.local and storage.sync.

• local — stays on this device, larger quota
• sync — syncs across the user's signed-in browsers, smaller quota

Use storage.sync for user preferences you want to follow them everywhere, like theme or settings. Keep the data small.

Use storage.local for larger or device-specific data such as caches, logs, or downloaded content that does not need to sync.

storage.sync is intentionally small. Roughly: about 100 KB total, 8 KB per item, and a limited number of writes per minute.

Exceeding these throws errors, so plan your data shape.

storage.local allows far more, commonly around 10 MB by default, and the unlimitedStorage permission can raise it. Still avoid storing huge blobs.

Both areas read with get. Pass a key, an array of keys, or an object of defaults.

The onChanged event fires whenever stored values change, even from another context. Use it to keep your UI in sync.

Delete specific keys with remove, or wipe an entire area with clear.

Use getBytesInUse to see how close you are to the quota before writing more data.

Sync writes can fail on quota errors. Wrap writes in try/catch and fall back to local storage when sync is full.

A common pattern: keep small settings in sync, keep everything else in local. Never store secrets like tokens in plain storage, since extension storage is not encrypted.

Test your storage knowledge.

You compared storage areas:

• sync for small cross-device settings
• local for larger device data
• Respect quotas and check getBytesInUse
• React to onChanged
• Handle write failures and avoid storing secrets

Picking the right area keeps your data fast, durable, and within limits.