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Merkle inclusion proof
curl --request GET \
  --url https://utxo-indexer.api.umbraprivacy.com/v1/trees/{tree_index}/proof/{insertion_index}
{
  "root": "1a2b3c4d5e6f7890abcdef1234567890abcdef1234567890abcdef1234567890ab",
  "tree_index": 0,
  "insertion_index": 42,
  "proof": [
    "0000000000000000000000000000000000000000000000000000000000000000",
    "2098f5fb9e239eab3ceac3f27b81e481dc3124d55ffed523a839ee8446b64864"
  ],
  "leaf": "deadbeefcafebabe1234567890abcdef1234567890abcdef1234567890abcdef12"
}
Returns an authentication path of 20 sibling hashes — one per level — ordered from the leaf level (index 0) up to the root level (index 19). All hash values are little-endian 64-character hex strings (32 bytes each).
Merkle proofs become stale when new leaves are inserted into the tree (because the root changes). The V18 burner factories fetch a per-batch proof immediately before submitting the burn, so simply re-run the burner on a stale-root failure — it refetches the proof. Never cache proofs across operations.

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Verifying a Proof

Hash the target leaf with each sibling in order and compare the final result to the tree’s current root hash (fetch the root via Tree Metadata).

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Usage in the SDK

The Umbra SDK does not use this single-proof endpoint when burning. Burner factories use the batch endpoint so all proofs in a burn batch share the same root. The single-proof endpoint exists for analytics, debugging, and custom integrations.

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Performance

Proof generation traverses all 20 tree levels. Under normal conditions, proofs are generated in under 100 ms. Operations exceeding 500 ms emit a slow-operation warning server-side but still return a valid proof.

Path Parameters

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tree_index
integer<int64>
required

Zero-based index of the Merkle tree to query.

Required range: x >= 0
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insertion_index
integer<int64>
required

Zero-based leaf position for which to generate the proof. Must be strictly less than the tree's current num_leaves.

Required range: x >= 0

Response

Merkle proof generated successfully.

Protobuf ProofResponse message returned by GET /v1/trees/{tree_index}/proof/{insertion_index}.

All hash string fields are little-endian hex representations of 32-byte Poseidon hashes (matching Solana's on-chain byte order and Circom ZK circuit input conventions). Each hash is a 64-character hex string (32 bytes).

Usage: Together with leaf, root, and the 20-element proof array, a caller can verify membership and construct a Groth16 zero-knowledge proof verifiable against the on-chain Umbra Merkle root.

Depth: The Umbra mixer uses a depth-20 Indexed Merkle Tree, so proof always contains exactly 20 sibling hashes.

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root
string
required

Little-endian hex-encoded Poseidon root hash at query time. 64 hex characters (32 bytes).

Example:

"1a2b3c4d5e6f7890abcdef1234567890abcdef1234567890abcdef1234567890ab"

​
tree_index
integer<int64>
required

Echo of the requested tree_index path parameter.

Example:

0

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insertion_index
integer<int64>
required

Echo of the requested insertion_index path parameter.

Example:

42

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proof
string[]
required

Ordered sibling hashes forming the authentication path from the leaf up to the root. Always exactly 20 elements (depth-20 tree), ordered from leaf level (index 0) to root level (index 19). Each element is a 64-character little-endian hex-encoded Poseidon hash.

Required array length: 20 elements
Example:
[
  "0000000000000000000000000000000000000000000000000000000000000000",
  "2098f5fb9e239eab3ceac3f27b81e481dc3124d55ffed523a839ee8446b64864"
]
​
leaf
string
required

Little-endian hex-encoded final_commitment = Poseidon(h1_hash, h2_hash) at insertion_index. 64 hex characters (32 bytes).

Example:

"deadbeefcafebabe1234567890abcdef1234567890abcdef1234567890abcdef12"