Open Source on CodeInstances.com

CodeInstances Launches as an Open Source Tool That Keeps Program Runs and Replays Them

Sun, 18 Oct 2026 00:00:00 +0000

CodeInstances v0.1.0 is out. It’s a small command-line tool that keeps a run of any program as a file and replays it later, with the network replaced by what was recorded. It’s open source under the Apache License 2.0 and comes as a single static binary for Linux, macOS and Windows.

The problem it goes after is an old one. Code is kept with great care, in version control, reviewed and tagged. Runs are thrown away. A test fails in CI, someone hits rerun, it passes, and whatever went wrong is gone along with the evidence. An API answers something strange once and never again. A job breaks on Tuesday, and by Wednesday the data it read has moved on.

How a Bug Report Can Arrive as a Runnable CodeInstances File

Sun, 18 Oct 2026 00:00:00 +0000

You maintain a command-line tool that talks to an online service. An issue comes in: “sync breaks against our account”. You don’t have their account. You can’t see their data. You ask for logs, then a bigger log, then a screen share, and after a week of back and forth you still haven’t seen the failure happen.

The reporter could send the failure itself. If they run your tool under CodeInstances, the run is kept as a file with every request your tool made and every answer their account gave back:

The CodeInstances File Format Is Open JSON With a SHA-256 ID

Sun, 18 Oct 2026 00:00:00 +0000

The file is the product. A tool can be replaced, but a run you kept in a format only one tool reads is a run you’ll lose eventually. So the instance format is open JSON, written down in full in FORMAT.md for anyone who wants to read or write instances with their own tools.

Its name is codeinstances/0, and that string is the first member of every file. A reader that sees a format version it doesn’t know has to refuse the file, and readers ignore members they don’t recognise. A file that holds the same member twice, or a known member spelled in another case, is refused. That’s how the format can grow without breaking files that already exist.