What BlockTracer is

A block explorer where a transaction is a debugging session. A transaction does the same thing every time it runs, so its whole execution can be recorded and replayed — not reduced to what went in and what came out. It is the deepest view into a transaction there is, built on CodeTracer, a time-travel debugger for ordinary software. Open source and free to use: a public good.

What you can do

Step and rewind: Move through a transaction one instruction at a time, forwards or backwards. Nothing re-runs — the whole execution is already recorded, so going back is as fast as going on.
See the values: Every line shows the values it touched, as they were at the point the session is stopped.
Read the call trace: The full tree of calls at a glance, with how much work each one did and where it went.
Read the source: Where the source is published, you step through the program as it was written. Where it is not, you step through the instructions instead.
Across chains and languages: The same session, whatever the chain, the VM or the language it was written in.
Go back as far as you like: Page through an address's entire history. Nothing is cut off at a row limit, and the oldest page is no slower to load than the newest.

What it costs you

No account: Reading is anonymous — every published trace opens without an account. You need one only to ask for a trace that does not exist yet, because generating it replays the transaction on our hardware. The result is then public for everyone.
No ads: There is no advertising and no market-data widget. Neither helps you understand a transaction.
No tracking: No third-party requests at all, so there is nothing here to track you with. This site keeps its own CDN logs and nothing else, and leaves nothing on your machine beyond the ordinary browser cache.

How it works

Every page here is a static file. Your browser downloads it and nothing else happens — no API, no database, no request to anyone else. That is why there is nothing here to track you with.

Chains published: 4
Third parties: None
Account: Not required to read anything

What it will not do

Guess: Where a fact is not published, the page says so instead of guessing at it. You are never shown a value that was not recorded.
Ask anyone else: No page calls out to a node or any other service to fill a gap. What you see is what was published, from one source.