tx_builder

Ergonomic Cardano transaction builder built on top of cardano-serialization-lib (CSL). Focused on dApp / Plutus script interactions and full Conway-era governance.

Scope

• Build only. You bring your own selected UTxOs and an external signer. build() returns an unsigned csl::Transaction with the witness set already populated for scripts / datums / redeemers — just attach Vkeywitness entries on the signing side.
• No coin selection, no provider integration, no signing. Those concerns live elsewhere by design — keeping this layer thin makes it composable.

What's in the box

Area	API
Inputs	SpendingInput::Pubkey / Plutus / NativeScript
Reference inputs	add_reference_input (or implicit via ScriptSource::Reference)
Outputs	Output::new(addr).lovelace(..).assets(..).inline_datum(..).script_ref(..)
Collateral	add_collateral, collateral_return, total_collateral
Mint / burn	MintAction::plutus(..) / MintAction::native(..) with signed quantities
Certificates	Cert::* for staking and all Conway-era flavors
Withdrawals	add_withdrawal, add_plutus_withdrawal
Governance — voting	add_vote(Vote { voter, action, choice, anchor })
Governance — proposals	add_proposal(ProposalSpec { .. })
Validity	validity_start, ttl
Metadata	metadata(label, datum), auxiliary_script

Example

See examples/plutus_spend.rs for a Plutus spend + mint with a reference script and collateral.

Minimal pubkey-only transfer:

use tx_builder::prelude::*;

let tx = {
    let mut b = TxBuilder::new(&params);
    b.change_address(&wallet)
     .add_pubkey_input(&utxo)
     .add_output(Output::new(&dest).lovelace(2_000_000))
     .ttl(100_000_000);
    b.build()?
};

let cbor = hex::encode(tx.to_bytes());

Build pipeline

TxBuilder::build() walks this fixed order, mirroring what CSL needs:

1. Inputs (regular + Plutus + native-script).
2. Reference inputs (explicit + implicit from ScriptSource::Reference).
3. Outputs.
4. Collateral inputs / return / total.
5. Required signers.
6. Mint.
7. Certificates.
8. Withdrawals.
9. Voting & proposals.
10. Validity range.
11. Metadata + auxiliary scripts.
12. Script-data hash (only if Plutus witnesses present).
13. add_change_if_needed(change).
14. build_tx().

Known sharp edges

• Ex-units are placeholders. Pass the csl::ExUnits you get from an evaluator (Ogmios evaluateTransaction, Blockfrost tx/evaluate, your own aiken simulate, etc.). The values you give to SpendingInput::plutus / MintAction::plutus are used verbatim — there's no on-the-fly evaluation in this crate.
• Redeemer indices. CSL fixes the index after sorting inputs / mints — the 0 placeholders inside the builder are intentional.
• CSL method-name drift. CSL is in active development; if a method like set_collateral_return_and_total or add_with_plutus_witness has been renamed between minor versions, you'll get a clear compile error and a one-line fix.
• Cost models. Pass all cost models you might need (PlutusV1/V2/V3) in ProtocolParameters::cost_models. CSL hashes only the ones referenced, so over-supplying is safe.

Alternatives worth knowing

• cardano-multiplatform-lib — dcSpark's fork of CSL with a different design.
• pallas-txbuilder — Rust-native (no WASM lineage), part of the broader Pallas stack.

For pure-Rust environments (no JS interop) pallas-txbuilder is often cleaner; this crate is the right pick when you're already locked to CSL.