KV now supports atomic conditional writes: create a key only if it doesn't exist, or update and delete a key only if it hasn't changed since you read it.

It works through versions. Every read returns the entry's current version. Pass it back as ifVersion and the write only happens if the key is still at that version. Pass ifVersion: null and the write only happens if the key doesn't exist yet:

const jobs = kv("jobs")

// Exactly one worker can create the key
const claimed = await jobs.setJson(jobId, { worker: workerId }, {
  ifVersion: null, // only write if the key doesn't exist
  ttl: 300,
})

if (!claimed) return // another worker already claimed it

When the condition fails, the write returns false instead of throwing. That is all you need for locks, counters, and idempotency keys that stay correct when two workers race.

Under the hood each cloud's native primitive does the work: DynamoDB condition expressions, Firestore preconditions, Azure Table Storage ETags, and an atomic upsert in local dev. Identical semantics everywhere, in TypeScript and Rust.

Read the docs →