# Transaction ID (TXID)

Source URL: https://help.blockstream.com/education/glossary/transaction-id-txid
Updated: 2026-05-26T17:15:12.000Z
Letter: T

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A Transaction ID (TXID) is a unique 64-character hexadecimal hash that serves as the permanent, immutable identifier for a specific Bitcoin transaction. Derived from double-hashing the transaction's serialized data, it enables anyone to locate, verify, and reference the transaction on the blockchain or via APIs, ensuring transparency and auditability.

#### Practical Examples

- After sending bitcoin from your wallet, copy the TXID and paste it into a [blockchain explorer](https://help.blockstream.com/%5F%5FGHOST%5FURL%5F%5F/blockchain-explorer/) like Blockstream.info to view details, including inputs, outputs, fees, and [confirmations](https://help.blockstream.com/%5F%5FGHOST%5FURL%5F%5F/confirmation/).
- In a multisig setup, share the TXID with co-signers to confirm the [transaction](https://help.blockstream.com/%5F%5FGHOST%5FURL%5F%5F/transaction/) has been broadcast and included in a [block](https://support.dxp-staging.blockstream.com/education/glossary/block), verifying shared custody.
- Use the TXID in API calls to Blockstream's explorer service to automate balance checks for an [address](https://help.blockstream.com/%5F%5FGHOST%5FURL%5F%5F/address/) in a custom app, tracking incoming payments without running a [full node](https://help.blockstream.com/%5F%5FGHOST%5FURL%5F%5F/full-node/).
- During disputes, provide the TXID to a support team; they can instantly inspect the on-chain record to resolve issues like double-spends or fee disputes.

#### Key Takeaways

- TXIDs are generated via SHA-256 double hash of the transaction's binary representation, making them collision-resistant and unique forever.
- They are case-insensitive but conventionally lowercase; any alteration to the transaction (e.g., fee change) produces a new TXID.
- TXIDs facilitate [broadcast transaction](https://support.dxp-staging.blockstream.com/education/glossary/broadcast-transaction) tracking and are essential for tools like [fee estimates](https://support.dxp-staging.blockstream.com/education/glossary/fee-estimates) and Replace-By-Fee (RBF).
- Public and verifiable by all, TXIDs underscore Bitcoin's open ledger, unlike proprietary transaction IDs in centralized systems.

#### In-Depth Explanation

When constructing a [transaction](https://help.blockstream.com/%5F%5FGHOST%5FURL%5F%5F/transaction/), wallet software assembles inputs (references to unspent outputs via previous TXID and output index), outputs (amounts locked to [addresses](https://help.blockstream.com/%5F%5FGHOST%5FURL%5F%5F/address/) via scripts), and metadata like fees and locktime. This structure is serialized into a binary format, then double-hashed with SHA-256 (first hash of the data, then hash of that result) to yield the 256-bit (32-byte) TXID, typically displayed as 64 hex characters. For [SegWit](https://help.blockstream.com/%5F%5FGHOST%5FURL%5F%5F/segwit/) transactions, the witness data is excluded from the TXID calculation to prevent malleability, ensuring stability for replacement mechanisms like RBF (BIP125). Upon [broadcast transaction](https://support.dxp-staging.blockstream.com/education/glossary/broadcast-transaction), the TXID propagates through the network; once mined into a [block](https://support.dxp-staging.blockstream.com/education/glossary/block), it becomes part of the [blockchain](https://support.dxp-staging.blockstream.com/education/glossary/blockchain) at a specific [block height](https://support.dxp-staging.blockstream.com/education/glossary/block-height). Explorers index TXIDs for quick retrieval, displaying decoded elements like scriptPubKey, signatures, and UTXO changes. This self-verifying nature means TXIDs are tamper-evident: even a single bit flip alters the hash entirely, providing cryptographic proof of integrity without trusted third parties.

#### Why Bitcoiners Care

TXIDs make Bitcoin auditable and trustless. Anyone can independently verify payment history and confirmation status on a blockchain explorer like blockstream.info without asking a bank or custodian.

Navigation: Blockstream Help Center > Education > Glossary > Transaction ID (TXID)

## Related Terms in This Letter
- [Timelocks](https://help.blockstream.com/education/glossary/timelocks)
- [Transaction ID (TXID)](https://help.blockstream.com/education/glossary/transaction-id-txid) (current)