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+# World Chain Builder API Spec
+
+### **Transaction Envelope**
+
+The PBH transaction envelope consists of an EIP 2718 RLP encoded transaction envelope concatenated with the RLP encoded `PbhPayload`
+
+References: 
+-  [Pbh Payload](https://github.com/worldcoin/world-chain/blob/8d60a1e79dbb3be68db075d49b3d0a8a67e45b3e/world-chain-builder/src/pbh/payload.rs#L50)
+-  [Pooled Transaction](https://github.com/worldcoin/world-chain/blob/8d60a1e79dbb3be68db075d49b3d0a8a67e45b3e/world-chain-builder/src/primitives.rs#L14)
+
+```rust
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct WorldChainPooledTransactionsElement {
+    pub inner: PooledTransactionsElement,
+    pub pbh_payload: Option<PbhPayload>,
+}
+
+/// The payload of a PBH transaction
+///
+/// Contains the semaphore proof and relevent metadata
+/// required to to verify the pbh transaction.
+#[derive(Clone, Debug, RlpEncodable, RlpDecodable, PartialEq, Eq, Default)]
+pub struct PbhPayload {
+    /// A string containing a prefix, the date marker, and the pbh nonce
+    pub external_nullifier: String,
+    /// A nullifier hash used to keep track of
+    /// previously used pbh transactions
+    pub nullifier_hash: Field,
+    /// The root of the merkle tree for which this proof
+    /// was generated
+    pub root: Field,
+    /// The actual semaphore proof verifying that the sender
+    /// is included in the set of orb verified users
+    pub proof: Proof,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Proof(pub semaphore::protocol::Proof);
+
+// Raw Transaction Envelope encoding
+impl WorldChainPooledTransactionsElement {
+		pub fn encode_enveloped(&self, out: &mut dyn alloy_rlp::BufMut) {
+		        self.inner.encode_enveloped(out);
+		        if let Some(pbh_payload) = &self.pbh_payload {
+		            pbh_payload.encode(out);
+		        }
+		 }
+}
+	  
+```
+
+**External Nullifier**
+
+Schema: `vv-mmyyyy-nn`
+
+Version Prefix: `v1`
+> Validation: Version matches current version.
+
+Date: `01-2025`
+> Validation: Month/Year matches current Month Year 
+
+PBH Nonce: `u16`:
+> Validation: PBH Nonce must be ≤ 30 by default. It is used to rate limit the amount of PBH transactions that can be sent in any given month. This value should reset at the beginning of each month monotonically increasing from 0→ `num_pbh_txs` . Any nonce > `num_pbh_txs` set on launch of the builder will be invalidated and not be inserted into the transaction pool.
+
+**Nullifier Hash**
+
+> Validation: Must be unique at the time of transaction validation.
+
+**Root**
+
+> Validation: Must be identical to the `latestRoot` in storage of the `OpWorldId` contract on L2.
+
+Additional Considerations: If a root has not yet been synchronized with l1. There is a window in which a valid proof will be seen as invalid in the transaction validator. A robust approach would be to read the root on l2, and assert it matches the root on l1 prior to sending the transaction to prevent a transaction validation error response.
+
+### **Builder API**
+
+The custom PBH transaction envelope must be sent to the builder’s public rpc through a `eth_sendRawTransaction` JSON RPC request. 
+
+Additional References:
+
+[**Building a Raw PBH Transaction Envelope from ORB Sequencer Reference**](https://github.com/worldcoin/world-chain/blob/8d60a1e79dbb3be68db075d49b3d0a8a67e45b3e/world-chain-builder/crates/toolkit/README.md)
+
+[**Sending a Raw PBH Transaction to the Builder Reference:**](ttps://github.com/worldcoin/world-chain/blob/8d60a1e79dbb3be68db075d49b3d0a8a67e45b3e/world-chain-builder/crates/assertor/src/main.rs#L119)