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What causes an intent hash mismatch?

The intent_hash_mismatch error occurs during raw validation (POST /api/validate/raw) when the intentHash submitted by the client does not match the server’s recomputation from the same transaction parameters. The server computes its own hash from the parameters you send and compares it to your submitted hash. Any difference in formatting, casing, or value causes a mismatch.
This error only applies to raw validation. Action-based validation (POST /validate) does not use intent hashes. If you are building a new integration, use action-based validation and skip this page entirely.

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The canonical hash format

The intent hash is computed as: 
intentHash = keccak256("<chainId>|<nonce>|<to_lower>|<calldata_lower>|<valueWei>|<gasLimit>|<maxFeePerGas>|<maxPriorityFeePerGas>|<txType>|<accessList_json>")
Every field must match exactly. The server uses the same formula with the parameters from your request body.

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Debugging checklist

Work through these 7 checks in order. Most mismatches are caused by items 1 through 3.

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1. Verify the nonce is current

The nonce must be the next unused nonce for the sending address. If you fetched the nonce earlier and another transaction was sent in between, your nonce is stale. Fetch the nonce immediately before computing the hash. 
const nonce = await publicClient.getTransactionCount({ address: walletAddress });

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2. Lowercase all addresses

The to field must be lowercase in the hash computation. The most common mistake is using a checksummed (mixed-case) address. 
// Wrong: checksummed address
const to = '0x036CbD53842c5426634e7929541eC2318f3dCF7e';

// Correct: lowercase
const to = '0x036cbd53842c5426634e7929541ec2318f3dcf7e';

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3. Gas estimation may differ

If you estimate gas, then compute the hash, then re-estimate gas, the values may change. Use fixed gas values during testing. In production, estimate once and use the same values for both the hash and the transaction. 
const gasLimit = '90000';
const maxFeePerGas = '1000000000';
const maxPriorityFeePerGas = '1000000000';
// Use these exact values in both the hash and the API request

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4. accessList must be an empty array

The accessList field must be [] (an empty JSON array), not undefined, null, or omitted. The server serializes it as "[]" in the canonical string. 
// Wrong
const accessList = undefined;

// Correct
const accessList = [];

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5. txType must be 2

The txType field must be 2 (EIP-1559). Type 0 (legacy) and type 1 (EIP-2930) transactions are not supported.

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6. Calldata must include 0x prefix and be lowercase

The calldata field must start with 0x and use lowercase hex characters. 
// Wrong: no prefix
const calldata = 'a9059cbb000000000000000000000000...';

// Wrong: uppercase
const calldata = '0xA9059CBB000000000000000000000000...';

// Correct
const calldata = '0xa9059cbb000000000000000000000000...';

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7. valueWei must be a string

The valueWei field must be a string, not a BigInt or number. JavaScript’s BigInt does not serialize to JSON the same way as a string. 
// Wrong: BigInt
const valueWei = 0n;

// Wrong: number
const valueWei = 0;

// Correct: string
const valueWei = '0';

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Use the SDK function

The safest approach is to use the SDK’s computeIntentHash() function. It handles all formatting, casing, and serialization automatically. 
import { computeIntentHash } from '@mandate.md/sdk';

const intentHash = computeIntentHash({
  chainId: 84532,
  nonce: 42,
  to: '0x036CbD53842c5426634e7929541eC2318f3dCF7e', // checksummed is fine, SDK lowercases
  calldata: '0xa9059cbb...',
  valueWei: '0',
  gasLimit: '90000',
  maxFeePerGas: '1000000000',
  maxPriorityFeePerGas: '1000000000',
  txType: 2,
  accessList: [],
});
The function normalizes all inputs before hashing. If you use computeIntentHash(), mismatches should not occur unless the nonce is stale.

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Still getting mismatches?

If you have verified all 7 items and the error persists, log the canonical string before hashing and compare it character by character with the expected format: 
const canonical = `${chainId}|${nonce}|${to.toLowerCase()}|${calldata.toLowerCase()}|${valueWei}|${gasLimit}|${maxFeePerGas}|${maxPriorityFeePerGas}|${txType}|${JSON.stringify(accessList)}`;
console.log('Canonical string:', canonical);
console.log('Hash:', keccak256(toBytes(canonical)));

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Next Steps

Intent Hash Concepts

How the intent hash binds validation to execution.

SDK computeIntentHash

SDK function reference for hash computation.

Common Errors

Solutions for other frequent Mandate errors.