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Signing is high-stakes: a double-send is a real-world incident. Atlas makes all state-changing operations idempotent so that network retries are always safe — a retried call cannot double-create or double-send.

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How it works

State-changing requests accept an idempotency key. Atlas remembers the first request made with a given key and returns the same result for any retry that reuses it, instead of performing the operation again. 
curl -X POST https://api-atlaswork.vercel.app/api/v1/envelopes \
  -H "Authorization: Bearer $ATLAS_API_KEY" \
  -H "Idempotency-Key: 8f1c2b9a-..." \
  -H "Content-Type: application/json" \
  -d '{ "...": "..." }'
Generate one key per logical operation (for example, a UUID created before the first attempt) and reuse it across retries of that same operation. Use a fresh key for a genuinely new operation.

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The SDK supplies keys automatically

The TypeScript SDK auto-supplies an idempotency key for every write, so retries through the SDK are safe by default — you don’t have to manage keys yourself unless you want explicit control.

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On the MCP surface

Every write an agent performs through the MCP server is idempotent by default. This is deliberate: agents retry, and a retried tool call must never double-send a contract. See the MCP tools reference for per-tool behavior.
Idempotency pairs with the review-first default: even if an agent retries the “send for review” call, the human still approves exactly one envelope.