Adobe brackets: write spaces instead of tabs

In the lower-right of the status bar you should see an indicator saying "Tab Size." Click the label to toggle to spaces. To change the amount of indent, click the number next to it and type a new value.

Note: if the indicator already says "Spaces" then Brackets should be using spaces instead of tab characters already. But it might not feel that way because when you move the cursor or press Backspace, there's a "soft tabs" behavior: the cursor will smartly skips over contiguous spaces to line up evenly with the next tab stop. If that bothers you, there will be a preference in the next release of Brackets (Sprint 38) to disable that behavior, making the cursor never move more than one space at a time.

For language specific control, Brackets allows you to provide different tab and space indentation values in the brackets.json file. For example:

"language": {
    "html": {
        "spaceUnits": 4
    },
    "javascript": {
        "tabSize": 2
    }
}