Bitcoin Script Online Debugger

Bitcoin Script Online Debugger Review: Stop Guessing, Start Stepping Through Your Stack

Ever tried to read a Script error and thought, “Okay… but what actually broke?”

If you’ve ever wished you could run Bitcoin Script right in your browser, step through each opcode, and watch the stack change in real time, you’re in the right place. The Bitcoin Script Online Debugger promises exactly that. No node setup, no scary CLIs—just a clean window into what Script is doing and why it fails or passes.

I test Script tools so you don’t waste hours chasing ghost bugs. Whether you’re learning the basics, prototyping a custom spend, or sanity-checking stack logic, this one can save you serious time.

Where Script debugging hurts (and why people give up)

Bitcoin Script isn’t hard because it’s huge—it’s hard because it’s precise. Small mistakes ruin everything, and the feedback can be maddeningly vague. Here are the common pain points I see over and over:

• Vague or contextless errors: You get “script failed” with no helpful breadcrumb trail.


• Strict stack rules: Misordered pushes or off-by-one items are easy to miss and hard to fix without a live stack view.


• Overkill setups: Spinning up test transactions just to check OP_DUP + OP_HASH160 logic is a lot of unnecessary friction.


• Intimidating tooling: Local CLIs are powerful but unfriendly, especially when you’re still learning.

Quick note: research on programming education shows that instant, visual feedback shortens learning curves and reduces errors. A step-through stack view hits that sweet spot for Script.

The simple fix you actually need

Open your browser, paste or write a script, and click Step. That’s it. The Bitcoin Script Online Debugger gives you:

• Run/Step controls: Execute the whole script or move opcode-by-opcode.


• Live stack view: See exactly how each opcode changes the stack (and alt stack).


• Immediate feedback: Spot where it fails and which item is wrong—fast.

It’s not trying to be a full node or a wallet. It’s a focused Script sandbox, which is exactly why it’s useful.

Who will get the most out of this

• Beginners: Learn how pushes, comparisons, and control flow actually behave.


• Developers: Prototype custom spend conditions and verify stack order quickly.


• Auditors/Reviewers: Do rapid sanity checks on redeem scripts and common patterns.


• Educators: Show students what OP_DUP, OP_HASH160, and VERIFY ops really do—live.

Quick verdict upfront

Simple, fast, and surprisingly helpful for learning and quick script checks. It shines when you need to:

• Confirm stack order for P2PKH/P2SH-style patterns


• Check control flow and pushdata correctness


• Explain opcodes visually without spinning up a node

But keep your hygiene: don’t paste private keys or real signatures you care about, and don’t treat a green pass here as full on-chain validation. Think of it as an educational, high-signal sandbox for catching logic and ordering mistakes.

Want to know exactly what this tool is—and what it isn’t—before you try it? In the next section, I’ll break that down and show you how to avoid false confidence while still moving faster. Ready?

What the Bitcoin Script Online Debugger is (and isn’t)

A browser-based Script runner where you paste/write a script, run it step-by-step, and watch the stack, alt stack, and error states change

Open the debugger, type or paste a Script, and hit run or step. That’s the experience. No installs, no node sync, just instant feedback on how each opcode reshapes the stack. The interface highlights the current opcode, shows the main stack and alt stack, and flags errors as soon as something invalid happens.

I love tools that make invisible state visible. Script is notoriously terse, and one wrong push or VERIFY can leave you guessing. Here, you literally see:

• Live stack updates after every opcode (top-of-stack clearly indicated)


• Alt stack to track moves with OP_TOALTSTACK/OP_FROMALTSTACK


• Error state when an opcode fails (e.g., empty stack pop, VERIFY fail)


• Execution pointer to know which opcode just ran and what’s next

Here’s a tiny sanity-check example you can try:

Script: OP_1 OP_1 OP_EQUAL
What you’ll see: push 1 → push 1 → compare → true on the stack.

With a classic template like:

Script: OP_DUP OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG
Expectation: you’ll watch the stack grow with your pushes, then shrink as VERIFY and CHECKSIG evaluate. The value isn’t just “pass or fail”—it’s the sequence that teaches you what went wrong or right.

“The stack never lies—it only repeats what you told it to do.”

A quick note: public documentation on Script behavior is excellent for cross-checking how things should behave—see the Bitcoin.org Developer Guide on Scripts and relevant BIPs (like minimal push rules in BIP62 and opcode changes since BIP66/141). I keep these open when I’m exploring edge cases.

What it’s not: a transaction builder, a wallet, or a full node

This is a Script simulator, not a wallet or broadcaster. It doesn’t talk to the Bitcoin network, it won’t assemble or sign transactions for you, and it isn’t aware of full transaction context unless you simulate that via pushes.

• No broadcast: you’re not spending coins here—pure local logic checks.


• No wallet connection: no seed phrases, no UTXO selection.


• Crypto checks may be simplified: OP_CHECKSIG/OP_CHECKMULTISIG are often stubbed or rely on placeholder data. If a signature “passes” in the browser with a dummy, don’t mistake that for on-chain validity.

If you need full transaction-aware validation (sighashes, script path conditions, Taproot annex behavior, etc.), this tool is a learning and prototyping ally—not the final judge. That final judge is still your local, reproducible test setup.

Key things I look for

A Script debugger lives or dies on clarity and predictability. When I open a page like this, I check for:

• Clear stack visualization: top-of-stack orientation, hex vs numeric clarity, alt stack visibility


• Run/Step controls: instant full run plus opcode-by-opcode control


• Helpful error hints: point to the failing opcode, not just “false” at the end


• Example scripts: P2PKH, P2SH-style redeem scripts, and small control-flow samples


• Opcode coverage: the common set used in today’s standard templates


• Consistency: deterministic behavior that matches Script rules you’d expect from references and BIPs

A small real-world check I run: pushdata rigor. Minimal push rules (popularized in standardness policies like BIP62) trip people up. If the debugger highlights a non-minimal push or weird ScriptNum encoding (like negative zero), that’s gold for learning and QA.

Who should use it

If you’ve ever stared at a Script and wondered why it fails, this saves your weekend:

• Students of Script: understand each opcode by watching it mutate the stack in real time


• Developers: sanity-check pushdata, control flow branches, and redeem/witness script layouts before writing unit tests


• Reviewers/Auditors: quickly validate custom scripts or spending policies without wiring a full environment


• Educators: live demos that show “this is what OP_EQUALVERIFY just did” land so much better when the stack is visible

Want to see the quickest way to load a known-good sample, read the stack like a pro, and avoid the classic ordering mistakes that sink 80% of first attempts? Keep going—I’ll show you exactly how to use the debugger without getting stuck next.

Hands-on: how to use the debugger without getting stuck

"If you can’t see the stack, you’re not debugging—you’re guessing."

Start with a known-good sample

Open the tool in your browser: bitcoin-script-debugger.visvirial.com. Before attempting anything fancy, confirm that the UI behaves the way you expect. A simple “hash-lock” pattern is perfect because it avoids signature complexity and still teaches stack flow.

• Initial stack (witness/inputs): push a preimage like 68656c6c6f (hex for “hello”).


• Script:OP_SHA256 OP_EQUALVERIFY OP_TRUE

You can get the SHA-256 of “hello” (in ASCII) from any reputable hasher. It’s 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824. So the full example becomes:

• Inputs:68656c6c6f


• Script:OP_SHA256 2cf24d...b9824 OP_EQUALVERIFY OP_TRUE

Hit Step and watch it work: the preimage is hashed, compared to the expected value, verified, and finally leaves a true on the stack. This lets you confirm the UI and build confidence before moving to signature-based flows.

Why start this way? According to the worked-example effect in learning science, stepping through correct examples reduces cognitive load and speeds up skill-building. See: Worked-example effect and Cognitive Load Theory.

Input layout you’ll see

The interface is friendly once you know where to look:

• Script editor: where you type or paste Bitcoin Script opcodes and pushdata.


• Initial stack / witness: optional inputs that simulate what the unlocking data would push before the script runs.


• Controls:Run, Step, and Reset to control execution.


• Live stack view: shows the stack and alt stack updating after each opcode, along with program counter and any error state.

Run vs Step

Run executes everything and tells you pass/fail. It’s great once you’re confident.

Step moves one opcode at a time. This is where the learning happens—you’ll see exactly which opcode changes the stack in unexpected ways.

• Tip: When something breaks, Step back to the previous operation mentally and note what changed. You’ll fix issues faster than “Run and pray.”

Reading the stack

The top-of-stack rules your fate. Many Script bugs are just items in the wrong order, not bad logic.

• Example (P2PKH-like flow without signatures):
  
  
  
  • Initial stack:
  
  
  • Script:OP_DUP OP_HASH160 OP_EQUALVERIFY OP_TRUE
  
  
  • What you see while stepping:
    
    
    
    • OP_DUP: stack becomes 
    
    
    • OP_HASH160: stack becomes 
    
    
    • Push : stack becomes 
    
    
    • OP_EQUALVERIFY: compares the last two, fails if mismatched, otherwise removes both
    
    
    • OP_TRUE: leaves true on the stack
    
    
    
    
  
  
  
  


• Keep your eye on the top two items before a compare or verify—they’re the ones that get consumed.

Common errors to expect

• Empty stack: an opcode needs items but the stack’s short. For example, OP_EQUALVERIFY requires two items.


• Minimal encoding violations: pushdata isn’t minimally encoded. If the tool enforces standardness, how you push matters as much as what you push.


• Bad push sizes: a declared push length that doesn’t match actual bytes.


• VERIFY failures: OP_EQUALVERIFY or OP_CHECKSIGVERIFY consuming a false and halting execution.


• Disabled opcodes: using things like OP_CAT in non-Tapscript contexts can throw a disabled opcode error.

When an error occurs, look for two things:

• The failing opcode: the program counter usually highlights it.


• The last known good stack state: what were the top 2–3 items before the failure?

A quick workflow I use

• 1) Sketch the expected stack after each step on paper or comments. It sounds old-school, but it works fast.


• 2) Paste your script and add initial inputs (witness/stack) that represent real-world unlocking data.


• 3) Click Step and watch the live stack view after each opcode.


• 4) If it fails, fix push order or encoding first. Logic is rarely the culprit—order and encoding are.


• 5) Rerun with Step until you consistently end with true on the stack and no VERIFY errors.

Here are two practical patterns to practice:

• Hash preimage check (no signatures)
  
  
  
  • Inputs:
  
  
  • Script:OP_SHA256 OP_EQUAL
  
  
  • Goal: end with true.
  
  
  
  


• P2PKH-style logic without crypto (good for order practice)
  
  
  
  • Inputs:
  
  
  • Script:OP_DUP OP_HASH160 OP_EQUALVERIFY OP_TRUE
  
  
  • Goal: check you’re not mixing the compare order or mis-pushing the hash.
  
  
  
  

Want to layer in signatures later? Model the flow first, then replace OP_TRUE with OP_CHECKSIG and use placeholder data if the tool supports stubbing. If it doesn’t, you still learned the exact stack choreography you’ll need when you move to a full environment.

Curious which script families this approach nails and where it starts to bend—legacy, multisig, SegWit, even Taproot quirks? Let’s look at real coverage next and find the edges you should know before you trust the green checkmark.

Script coverage: what works well and where limits usually are

Legacy scripts

I get the best mileage with classic, non-SegWit logic. Think simple spends like P2PKH and the executed part of P2SH redeem scripts. If you paste something like OP_DUP OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG, the live stack view makes it obvious when you’ve misordered inputs or forgot a push. That’s where the tool shines—turning “Why is this false?” into “Oh, I see exactly where it flips.”

For P2SH-style flows, I often model the redeem script directly and simulate the pushes that would normally come from the scriptSig. Two quick wins you’ll notice:

• Ordering clarity: Put the redeem script at the end of the initial stack, then step through. You’ll catch off-by-one mistakes fast.


• Pushdata sanity: If a push is too long, short, or not minimally encoded, you’ll see the failure right where it happens (see BIP66/BIP62-style rules).

“The stack is brutally honest. It won’t do what you intended—only what you told it.”

Multisig

Yes, you can model OP_n OP_m OP_CHECKMULTISIG patterns and step through them to visualize how many signatures you’re accounting for. I like to set up a 2-of-3 redeem script and then play with the number and order of signatures in the initial stack. It’s a fast way to teach the infamous extra-dummy-element quirk of OP_CHECKMULTISIG.

• Remember the dummy: Traditional multisig requires a leading OP_0 (the “CHECKMULTISIG bug”). In SegWit contexts, BIP147 requires that dummy to be exactly zero.


• Reality check on sigs: Many browser debuggers simplify signature verification. A green check doesn’t mean a signature is valid on-chain. Treat it as structure validation, not crypto validation.


• Teaching tip: Try swapping the order of two signatures; watch how the script still passes if they match the right pubkeys. It’s a great way to internalize “signatures map to keys, not positions.”

SegWit notes

SegWit logic is still approachable: you can reason about what executes by modeling the witness pushes and the effective script.

• P2WPKH: The executed script mirrors legacy P2PKH; you simulate stack items as if they were witness data. You’ll understand control flow and stack shape, but not BIP143-style sighash details.


• P2WSH: Paste the witness script and set the witness stack like you would at spend time. Great for catching IF/ELSE paths and minimal push expectations.


• Context limitation: BIP143 transaction context and sighash construction won’t be complete in most web tools. Use this to get the logic right, then confirm signatures locally.

References worth bookmarking: BIP143 (SegWit sighash), Bitcoin Wiki: Script.

Taproot/Tapscript

Tapscript brought cleanups and new rules (BIP341/BIP342). Some online debuggers partially support it; others stub major parts. I treat Taproot tests here as educational unless the tool explicitly documents full support.

• No CHECKMULTISIG: Tapscript uses OP_CHECKSIGADD to build k-of-n. A 2-of-3 can look like:  CHECKSIG CHECKSIGADD CHECKSIGADD 2 NUMEQUAL.


• Different numeric rules: Tapscript moves to 64‑bit numeric semantics and enforces MINIMALIF (nonzero values for IF must be exactly 1). Many web tools miss these nuances.


• Annex and leaf versioning: Tapscript context (annex, leaf version, and signature hashing per BIP341/342) is tough to simulate in-browser. Don’t rely on it for production checks.

Dig deeper: BIP341 (Taproot) and BIP342 (Tapscript).

Crypto opcodes reality check

Here’s the honest truth: OP_CHECKSIG and OP_CHECKMULTISIG inside many browser debuggers are best treated as placeholders. They help you confirm stack positions and counts, not cryptographic truth.

• Use placeholders: Push mock signatures/pubkeys and confirm your control flow and stack cleanup are correct.


• Don’t over-trust green: A “true” result only tells you the logic passes under simplified checks. Real signatures require the exact transaction context and strict DER/Schnorr rules.


• Cross-check locally: For actual verification, switch to Bitcoin Core tests, btcdeb-style CLIs, or libraries that build sighashes per BIP66/143/341/342.

Encoding and ScriptNum quirks

Most “it should work!” moments die here. Encoding details are where scripts fail in the wild.

• Minimal pushes: Small integers should use dedicated opcodes (e.g., OP_1), not long pushdata. Minimal encoding is expected in many standard contexts (see BIP62-type policies).


• DER signatures (legacy/SegWit v0): BIP66 tightened DER rules; anything non-canonical is out. A simulator may skip this—mainnet won’t.


• Negative zero trap: 0x80 is “-0” and compares differently in some checks. If an IF branch misbehaves, make sure your “true” is actually 0x01, not some non-minimal nonzero.


• ScriptNum size limits: Pre-Tapscript numeric operations use a 4‑byte limit in consensus. Tapscript moves to 64‑bit. If your web tool doesn’t model this, you might see false positives.

Practical example you can try right now:

• Minimal IF: Push 0x02 before OP_IF in a Tapscript-style check. A correct Tapscript engine fails it because nonzero must be exactly 0x01. Many web tools won’t. That gap matters.


• Zero semantics: Compare pushing OP_0 vs pushing an empty vector via PUSHDATA(0). They’re equivalent “false,” but non-minimal encodings can fail policy checks.

If you’re thinking, “All right, this looks powerful—but how smooth is it to use under pressure, and can I trust it with real snippets without risking leaks?” Great questions. Let’s talk speed, stability, and safety next—because those details decide whether it becomes your daily tool or just a weekend toy.

UX, performance, and safety

Speed and stability

For short, bread‑and‑butter scripts, the Bitcoin Script Online Debugger feels snappy. Stepping through a P2PKH or a small P2SH redeem script is smooth, and the stack view keeps up with you without lag.

Things get sluggish when you stress the UI, not so much the Script VM rules. Visualizing the stack after every opcode is where browsers sweat a bit. Here’s what I noticed that can slow it down:

• Large hex pushes: Massive hex blobs force the DOM to update big chunks of text. If the tool enforces the standard 520‑byte element rule, you’ll hit that limit fast; if not, the UI can chug while painting huge items.


• Very long scripts: Dozens of opcodes are fine; hundreds start to feel heavy, especially with repeated stack mutations like OP_DUP and OP_TOALTSTACK back and forth.


• Constant step spam: Rapid‑fire clicking on “Step” can stack up UI work. Pause a beat and let the view settle, especially in mobile browsers.

“Fast is fun—until it hides a bug. The sweet spot is fast enough to flow, slow enough to see.”

Quick tip: if you’re modeling bigger constructions (e.g., multisig with many pubkeys), collapse data in your head and only expand when you need to inspect the exact bytes. You’ll keep the visual noise—and the browser—under control.

Desktop vs mobile

You can use this on a phone, but it’s night‑and‑day better on a laptop or a large monitor. Script is a stack language; seeing more of the stack and more of the code at once helps you spot ordering mistakes instantly.

• On mobile: rotate to landscape, reduce font size a touch, and consider a Bluetooth keyboard. Thumb‑typing long hex pushes is pain.


• On desktop: keep the editor and stack panel visible together. If the tool lets you undock or resize panes, do it. A wide view cuts your error rate.

Privacy and security

Assume anything typed into a web tool can be logged—by design or by accident. That’s not paranoia; the Princeton Web Transparency team showed how “session replay” scripts can capture full form inputs across the web. Treat this debugger the same way you’d treat a pastebin: no secrets, no private keys, no real signatures you care about.

• Never paste: private keys, seed phrases, internal xprv paths, real customer data.


• Use placeholders: swap a real DER signature for a same‑length dummy (e.g., 71 bytes of non‑sense), and label it clearly.


• Watch your clipboard: cloud‑synced clipboards and browser extensions can leak data. Keep sensitive material offline.


• Treat logs as public: anything you share via link or screenshot should be safe to publish.

If you want to practice “realistic” flows without risk, craft mock artifacts: a 33‑byte compressed pubkey filled with 02ffffffff…, a 20‑byte hash as 0000…deadbeef, etc. Your stack behavior stays realistic, your secrets stay yours.

No broadcast, no wallet connection

This is a pure simulator/visualizer. It won’t connect to your wallet, it won’t sign, and it won’t broadcast. That’s a feature for safety. You can experiment freely without worrying about bumping a UTXO or leaking wallet metadata.

That said, don’t confuse a green “pass” here with an on‑chain guarantee. Crypto checks may be simplified or stubbed. Think of it as a microscope for stack logic, not a notary for transactions.

Exporting and reproducibility

When you finally nail a tricky stack dance, lock it in so future‑you (or a teammate) can replay it exactly. If the tool offers shareable links or export, use them. If not, keep a compact “test case card” with the essentials:

• Script: the exact bytes or assembly you ran.


• Initial stack/witness: every push, in order, with byte lengths noted.


• Assumptions: any flags or rules you relied on (e.g., minimal pushes, NULLDUMMY, ScriptNum limits).


• Expected checkpoints: what the stack should look like after key opcodes (not just at the end).


• Tool/version/date: web tools evolve; lock the context to avoid “it worked last month” mysteries.

I like to store these alongside code in version control, and I stick to stable placeholders so a screenshot or a shared link still makes sense six months from now.

Want your scripts to feel fast, readable, and safe at the same time? Up next, I’m sharing the power workflow I use to build scripts incrementally, label pushes so they teach themselves, and catch ordering mistakes before they bite. Ready for a few field‑tested tricks that cut debugging time in half?

Power tips, teaching tricks, and when to choose another tool

Build scripts incrementally

I build scripts the same way I build unit tests: tiny change, immediate feedback. It slashes debugging time because you always know which exact step introduced the break.

• Start with pushes only. Confirm your inputs are what you think they are.


• Add one opcode. Step once. Check the stack. Repeat.


• If it fails, you’ve located the problem opcode without guesswork.

Example flow I use for a P2PKH-style check (educational, not a real tx context):

Step 1 (pushes only):

Goal: verify the debugger shows exactly these three items, in this order.

Step 2 (add OP_DUP):
OP_DUP
Expected stack after OP_DUP: [, , , ]

Step 3 (add OP_HASH160):
OP_DUP OP_HASH160
Expected: [, , , ]

Step 4 (add OP_EQUALVERIFY):
Expected: [, ] if hashes match; error if they don’t.

Step 5 (add OP_CHECKSIG):
Expect true if signature checks out under the tool’s rules; remember many web tools stub/relax crypto.

This “one opcode at a time” method isn’t just practical—it matches what learning science calls the worked-example effect and subgoal labeling. You reduce cognitive load by isolating each transformation on the stack (Sweller, 1988; Catrambone, 1998).

Name your pushes in comments

Labels stop you from mixing up hex blobs. If the editor supports comments, annotate each push so your future self (or a student) knows what’s what. If comments aren’t supported, keep a notes pane or a side list with labels.

With comments (if supported):
// signature for msg X (SIGHASH_ALL)
// 33-byte compressed key (02.../03...)
// RIPEMD160(SHA256(pubkey))

For multisig sketches, I’ll label counts too:

OP_2 // need 2 signatures
// Alice
// Bob
// Carol
OP_3 // three total keys
OP_CHECKMULTISIG

Teaching tip: I also assign short aliases in a legend, like A=Alice pubkey, S_A=Alice sig. Then I use those aliases in stack expectations so a group can follow the logic at a glance.

Compare expected vs actual stack

Before stepping, I write what I expect the stack to look like after each opcode. Then I step and compare. It’s a simple trick, but it catches most “oops, wrong order” issues that eat an afternoon.

• Write a two-column “ledger”: Opcode → Expected stack (top on the right).


• Run one step, check debugger’s stack vs your expected line.


• Mismatch? You just found a push order or hashing target mistake.

Here’s a compact P2SH-style sanity check:

Given stack (witness-like): [, ]
ScriptSig:  OP_HASH160 OP_EQUALVERIFY [then run redeemScript]

Expectations:
After push : [, , ]
After OP_HASH160: [, , h160(redeem)]
After push : [, , h160(redeem), h160(redeem)]
After OP_EQUALVERIFY: [, ]

Why this works: externalizing your mental model reduces working-memory load and improves error detection (cognitive load theory; testing effect, Bjork & Bjork). In plain English—you think clearer when the steps are written out.

When you need deeper checks

Some questions the browser can’t answer with certainty:

• Are signatures truly valid under the right SIGHASH and script version?


• Does this pass consensus rules in context (nLockTime, annex, Taproot leaf version, minimal encoding under Tapscript)?


• Are there malleability or policy edges (NULLFAIL, CLEANSTACK, MINIMALIF) that the web tool doesn’t model?

That’s when I switch to local, context-aware tools:

• Bitcoin Core regtest + script tests to evaluate real consensus behavior.


• btcdeb-style CLIs for opcode-by-opcode stepping with full Script semantics.


• Unit tests in rust-bitcoin/bitcoinlib/bitcoinjs-lib to lock behavior with fixtures.

Practical path I use: sketch logic online, then move to a local test where I produce real signatures with the exact transaction preimage, enforce minimal encoding, and assert final stack and error codes. The web tool gets me to “probably correct” fast; local checks get me to “production safe.”

Alternatives and complements

If you want a workflow that scales from napkin idea to production-ready:

• Sketch: Use the online debugger to shape the control flow and stack order.


• Transcribe: Copy the final script and pushes into a unit test. Hardcode expected stacks after key steps.


• Verify: Run the script in a local interpreter with realistic sighashes and flags (CLEANSTACK, VERIFYMINIMALIF, NULLFAIL).


• Stress: Add edge cases: empty sigs, non-minimal integers, negative zero, off-by-one key counts in multisig.


• Context: If using SegWit/Taproot, test with real witness construction and leaf versions.

Educator trick: set “gotcha drills.” For example, give students a script that fails because an item needs a SWAP before OP_CHECKSIG, or a multisig with OP_2/OP_3 reversed. Have them predict the stack, step through, spot the mismatch, and propose the smallest fix. This targets common real-world mistakes while building confidence.

Want a rapid-fire set of answers to the questions I get all the time—Is it free? Can I step opcode-by-opcode? What about Taproot and privacy? I’ll hit those next. Any specific question you want covered in the FAQ?

FAQ: quick answers people usually ask

Is the Bitcoin Script Online Debugger free to use?

Yes. It runs in your browser and doesn’t touch your wallet. You can open it here: bitcoin-script-debugger.visvirial.com.

There’s no broadcast, no node connection, and no login. Just write a script, hit Run or Step, and watch the stack.

Can I test P2PKH, P2SH, and multisig?

Absolutely—at the “executed script” level. You can model what runs on-chain after all the wrapping is peeled away and see the stack change opcode by opcode.

Example (P2PKH-like pattern):

Witness/stack you provide:

Script you run:OP_DUP OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG

Use placeholders for signatures and pubkeys and step through to confirm ordering and comparisons. For multisig, remember the historical quirk:

• OP_CHECKMULTISIG requires an extra dummy element (usually OP_0) before signatures due to the classic bug. A 2-of-3 layout looks like: OP_0 2 3 OP_CHECKMULTISIG

Heads-up: Signature validation in web tools is often stubbed. A “pass” in the UI doesn’t prove a real DER-encoded signature would verify on-chain.

Does it support Taproot/Tapscript?

Many web debuggers stop short of full Tapscript semantics (BIP340/341/342). If you need OP_CHECKSIGADD, annex handling, or precise sighash rules, double‑check the tool’s docs and then confirm locally.

For reference:

• BIP340 (Schnorr): Schnorr signatures for secp256k1


• BIP341 (Taproot): Taproot


• BIP342 (Tapscript): Tapscript

Practical approach: use the debugger to reason about stack logic, then replay the exact spend path with a local tool that enforces all Taproot rules.

Is my data private and secure?

Rule of thumb: act like anything you type could be logged.

Don’t paste real private keys, live signatures, or unreleased transaction data. Use dummy values like deadbeef for hashes and a 33‑byte or 65‑byte hex-looking placeholder for pubkeys. For teaching, I use fake DER-like blobs ending with a sighash byte 01 (SIGHASH_ALL) to illustrate structure without exposing secrets.

Can I step through opcodes one by one?

Yes—and that’s where the tool shines. Click Step to watch each opcode touch the stack and alt stack. A tiny example that helps students “get” alt stack:

• Initial stack: 2 3 4


• Script: OP_TOALTSTACK OP_ADD OP_FROMALTSTACK OP_ADD

Walkthrough:

• OP_TOALTSTACK: moves 4 to alt stack; main stack is 2 3


• OP_ADD: adds to 5; main stack is 5


• OP_FROMALTSTACK: brings back 4; main stack is 5 4


• OP_ADD: result 9

One step at a time makes ordering mistakes jump out.

What makes a script “pass” here?

In these tools, a “pass” usually means the script ran to completion and left a nonzero true on top of the stack without hitting VERIFY failures or runtime errors. That’s a simulation, not full network consensus validation.

Quick sanity example:

• Stack: 1 1


• Script: OP_EQUAL


• End state: true (nonzero) → pass

Contrast with encoding rules enforced on-chain (like strict DER per BIP66)—a web simulator might not catch those.

Will it broadcast transactions or spend coins?

No. It’s a visualizer. There’s no wallet connection and no broadcast. You’re just simulating how opcodes move data.

Where should I test for production-grade certainty?

Use battle-tested local tools that enforce consensus rules and transaction context:

• btcdeb (step through scripts with full control and tx context)


• Bitcoin Core on regtest/testnet for end-to-end creation, signing, and validation


• For Taproot, libraries that implement BIP340/341/342 accurately (e.g., Core’s functional tests or reputable SDKs)

Pro tip: sketch logic in the browser for speed, then lock it down locally with full validation. That combo catches most gotchas—from ScriptNum bounds to strict DER and minimal push rules.

Conclusion

Bottom line: the Bitcoin Script Online Debugger is a friendly way to learn Script and sanity‑check stack logic without friction. Use it to spot ordering mistakes, understand control flow, and teach concepts clearly. For real signatures, Taproot paths, and on-chain guarantees, confirm everything with local tools. That workflow is fast, safe, and reliable.