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.

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

Setting up idempotency headers

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

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

For full configuration details, see the docs for your API definition format: