Configure idempotency headers

For endpoints you’ve configured as idempotent, Fern’s SDKs allow users to specify idempotency headers for safe request retries. Typically the headers include Idempotency-Key, but you can also specify additional headers.

Generated SDK behavior

The generated SDKs expose idempotency headers as parameters only for endpoints marked as idempotent, ensuring users know exactly which invocations are idempotent.

const response = await client.transactions.send({
  amount: 100,
  currency: "usd",
}, {
  idempotencyKey: "64099353-b48b-4dcd-98b7-74df1cc57933"
});

Auto-generate idempotency keys

Generated SDKs can attach an idempotency-key header automatically, generating a UUIDv4 value for each request unless the caller supplies one. sdk-config.yml doesn’t have a setting for this yet. To turn it on with generators.yml, see Auto-generate idempotency keys in the Legacy docs.

Setting up idempotency headers

Configure the idempotency headers your API uses, then mark individual endpoints as idempotent:

x-fern-idempotency-headers:
  - header: IDEMPOTENCY-KEY
    name: idempotency_key
paths:
  /plants:
    post:
      x-fern-idempotent: true

For full configuration details, see Idempotency in OpenAPI.