Set up your config

MLabel cannot do anything without a config. It is the file that says what your data looks like and what you are being asked to record.

Getting one

If someone is running a labeling project for you, they will give you a .jsonc file. Save it somewhere you will find it again — next to the data you are labeling is a good default.

If you are setting up the project yourself, start from the annotated example in the repository, examples/config.jsonc, and read Anatomy of a config. Then check your work without launching the app:

pnpm validate path/to/your-config.jsonc

Loading one

There are four ways, in the order MLabel tries them:

1. A config next to the executable. On startup MLabel looks beside its own executable for a file named config.jsonc, mlabel.config.jsonc, or mlabel.jsonc, in that order. If it finds one, it loads it and you never see the config screen. This is how you ship the app and the config together.
2. The most recent config, if there was no adjacent one. MLabel remembers the last config you opened and reloads it on the next launch.
3. Drag and drop. Drop a .jsonc anywhere on the window.
4. The picker. Click Choose config and select the file.

Tip

Options 1 and 2 mean that in day-to-day use you normally launch MLabel and go straight to choosing a data file. The config screen is a first-run experience.

If the config is rejected

MLabel refuses to load a config it does not fully understand, and lists every problem at once rather than stopping at the first. Each one carries a line, a column and the path to the offending key.

The most common causes are a misspelled key (every object is strict — unknown keys are errors, not silently ignored) and a missing or wrong version. See Every error explained for the full catalogue.

Editor support

Point your config at the published JSON Schema and any editor that understands JSON Schema will autocomplete keys, offer only the values that are legal in context, and underline mistakes as you type:

{
  "$schema": "https://mlabel.vlad.gg/mlabel.schema.json",
  "version": 2,
  // …
}

This is worth doing even for a config someone else wrote — it turns “why won’t this load” into a squiggle under the exact character.

Next

Your first labeling run →