Analyze PSBTs Privately Before You Sign
A Partially Signed Bitcoin Transaction encodes everything about a spend — where the funds come from, where they go, and what fee you're paying. If you sign without reading it, you're trusting whoever constructed it. This tool decodes any PSBT server-side into structured, human-readable output so you can verify before your key touches the transaction. After the AI analysis, you get 5 free follow-up questions to ask about anything in the transaction.
Why This Matters
Never sign what you don't understand. A PSBT can send your entire UTXO set to an attacker's address with a single signature. Hardware wallets show limited information — often just the output addresses and amounts without context about change outputs, fee rates, or script conditions. Decoding the full PSBT before signing is the only way to know exactly what you're authorizing.
Most online PSBT decoders require you to paste sensitive transaction data into a website that logs requests, tracks sessions, or requires an account. That creates a permanent link between your IP address and your Bitcoin transaction graph. This tool decodes your PSBT without storing it, without cookies, and without accounts.
What the Decoder Shows You
Inputs & UTXOs
Every input with its previous transaction ID, output index, and value. You see exactly which UTXOs are being spent and their total value.
Outputs & Destinations
Every output address and amount, clearly labeled. Identify the payment destination vs. change output so you know where your sats are actually going.
Fee Calculation
Total fee in sats and the effective fee rate in sat/vB. Catch fee overpayment before you sign — a misconfigured transaction can burn thousands of sats unnecessarily.
Script Types & Signing Status
Identify P2PKH, P2SH, P2WPKH, P2WSH, P2TR scripts. See which inputs already have signatures and which still need signing — critical for multisig coordination.
How the Analysis Works Under the Hood
Your raw PSBT never reaches the AI model. The server decodes the PSBT first, extracting structured data — inputs, outputs, fees, script types, signing status. Only this structured representation is sent to the AI for analysis. This means the model works with clean, typed fields instead of opaque base64, producing more accurate and faster results.
Server-side decode. The PSBT is parsed on the server using a Bitcoin library. Raw base64 or hex is converted into structured JSON with typed fields for every input, output, fee, and script.
Date injection. The current date is injected into the analysis context so the model doesn't incorrectly flag future-dated timelocks or nLockTime values as suspicious. Without this, models hallucinate warnings about timestamps that are perfectly valid.
Fast, focused analysis. The AI runs on the Budget model with reasoning disabled. This is the cheapest and fastest configuration — no chain-of-thought overhead, just a direct plain-English explanation of what the transaction does and what to watch for.
5 Free Follow-up Questions
After the paid analysis, you get 5 free follow-up questions to dig deeper into the transaction. Questions and answers appear in a chat bubble format below the analysis, so you can have a back-and-forth conversation about what the PSBT contains.
Example follow-up conversation
3 of 5 follow-up questions remaining
For Humans
Real scenarios where PSBT analysis prevents costly mistakes
Multisig wallet verification
You receive a PSBT from a co-signer in a 2-of-3 multisig. Before adding your signature, decode it to confirm the destination address and amount match what was agreed. A compromised co-signer could swap the output address — you'd never know without decoding. Use your follow-up questions to ask about signing status and which keys have already signed.
Hardware wallet cross-check
Your hardware wallet shows "Send 0.05 BTC to bc1q..." but you want to verify the change output, fee rate, and that no extra outputs were added. Decode the PSBT independently before confirming on the device. Then ask follow-ups about whether the change derivation path matches your wallet.
CoinJoin participant review
Before signing your inputs into a collaborative transaction, verify that your output amount matches your input minus the expected fee. Confirm no unexpected outputs were added that would drain your funds.
Fee sanity check
Wallet software sometimes miscalculates fees during high-fee environments. Decode the PSBT to see the exact sat/vB rate before signing — especially important for large transactions where a 10x fee overpayment means real money. Ask a follow-up to compare against typical mempool rates.
How It Works
For Agents
Use cases for AI agents, automation pipelines, and developers
No API key needed. PSBT analysis uses L402 — the raw decode is free, and the AI analysis is 5 sats per request via Lightning. Each paid analysis includes 5 free follow-up questions. Agents send a PSBT string, receive structured JSON back. No quota, no rate limits on the free tier.
Automated transaction review
Before an agent co-signs a multisig transaction, it decodes the PSBT to verify outputs match expected parameters. If the destination or amount is wrong, the agent refuses to sign and alerts the operator. Follow-up questions let the agent drill into specific concerns programmatically.
Fee monitoring pipelines
Batch-decode PSBTs from a wallet's pending queue and flag any with fee rates above a threshold. Useful for treasury operations where overpaying fees at scale adds up quickly.
Wallet software testing
During development, decode PSBTs generated by your wallet to verify correct construction — right script types, proper change derivation paths, and accurate fee calculation.
Compliance & audit trail
Decode and log PSBT details before every signing operation. Creates a structured audit record of what was authorized, when, and by which signers — without exposing raw transaction data to third parties.
L402 Authentication Flow
# Decode a PSBT (free)
curl -X POST https://sats4ai.com/api/l402/bitcoin/psbt \
-H "Content-Type: application/json" \
-d '{"psbt":"cHNidP8BAH0CAAAAAQ..."}'
# Request AI analysis (returns 402 + 5-sat invoice)
curl -X POST https://sats4ai.com/api/l402/bitcoin/psbt \
-H "Content-Type: application/json" \
-d '{"psbt":"cHNidP8BAH0CAAAAAQ...","explain":true}'
# Pay the 5-sat invoice, then resend with proof
curl -X POST https://sats4ai.com/api/l402/bitcoin/psbt \
-H "Content-Type: application/json" \
-H "Authorization: L402 <token>:<preimage>" \
-d '{"psbt":"cHNidP8BAH0CAAAAAQ...","explain":true}'MCP & OpenClaw
Privacy by Design
- No accounts. No email, no username, no session tokens. Nothing links your PSBT to an identity.
- No storage. PSBTs are decoded server-side in memory and discarded. Nothing is written to disk or database.
- No raw data to AI. The AI model receives structured fields (addresses, amounts, script types) — not your raw PSBT bytes.
- No analytics on transaction data. We don't log addresses, amounts, or transaction IDs.
- Lightning payment. Pay with sats — no credit card or bank account that ties your identity to the request.
Chain with Other Services
Decode a PSBT, then ask an AI model to explain the implications — ideal for complex multisig or timelocked transactions.
Decode a PSBT and email the structured breakdown to co-signers for review before the signing round.
Decode a Lightning invoice to verify payment details, then analyze the underlying PSBT if you need on-chain settlement.
FAQ
What is a PSBT?
A Partially Signed Bitcoin Transaction (BIP 174) is a standard format for passing unsigned or partially signed transactions between wallets, hardware signers, and coordinators. It encodes all the information needed to sign and finalize a transaction.
Why should I decode a PSBT before signing?
Signing a PSBT authorizes spending your bitcoin. Without verifying the outputs, fee, and script conditions, you could send funds to the wrong address, overpay fees, or authorize an unintended spend path in a complex script.
Is my PSBT data stored?
No. The PSBT is decoded server-side in memory and discarded immediately. The AI model receives structured fields, not the raw PSBT. No transaction data is written to disk, logged, or associated with any identity.
What does the AI analysis add?
The free decode gives you raw structured data. The 5-sat AI analysis translates that into plain English — summarizing what the transaction does, flagging unusual patterns like high fees or uncommon script types. The current date is injected so timelocks and nLockTime values are evaluated correctly.
What are the 5 free follow-up questions?
After the paid analysis, you can ask 5 additional questions about the PSBT at no extra cost. These appear as chat bubbles below the analysis. Ask about specific outputs, fee rates, signing status, script conditions — anything about the transaction you want to understand better.
Decode Your PSBT — No Signup Required
Free structural decode. AI analysis for 5 sats + 5 free follow-up questions. All you need is a PSBT string and a Lightning wallet.