Is there an online simulator that would allow me to step through, debug, or simulate the execution of a Bitcoin script?
I know of these two:
The first one in particular I have found to be very useful.
Bitcoin Script debugging utilities.
This is a set of tools used to debug or construct scripts for use in Bitcoin.
btcdeb> help step Execute one instruction and iterate in the script. rewind Go back in time one instruction. stack Print stack content. altstack Print altstack content. vfexec Print vfexec content. exec Execute command. tf Transform a value using a given function. print Print script. help Show help information.
I've been looking for a tool to experiment with bitcoin script for a while now, and I finally finished developing one myself.
BitAuth IDE is an open source project for designing advanced scripts for bitcoin and bitcoin-like cryptocurrencies. It’s both a learning sandbox and a tool for designing new kinds of wallets.
It includes a live-updating, interactive, line-by-line debugger, which visualizes that state of the stack over the entire execution of the program. There's also an entity and variable system for automatically generating private keys, public keys, and correct signatures across locking and unlocking scripts.
You can use the online demo of BitAuth IDE.
And the source is on GitHub.
I've also assembled a much longer Bitcoin Script Reading List, which you might find useful. It includes links to several more related tools and script testing environments.
The github repository for the first link posted by StephenM347 can be found here
If you want to run it locally, clone the repo and then,
Launch a server from here. This will launch a server on port 8000.
python -m SimpleHTTPServer 8000
From the browser, visit localhost:8000, and select the file
There is a "Script Playground": http://www.crmarsh.com/script-playground/
I have a tool at http://www.bowmain.co.uk/BSV/ which may be use. Let me know what you think as I can make changes to it.