How does it decide what is nested under what?

By indentation. A line indented one unit deeper than the line above it becomes that line's child, and a line at the same or a shallower indent closes the levels above it. Leading dashes or numbers are ignored when the depth is read.

Can a line skip a level?

No. An outline may only descend one level at a time, so a line indented far deeper than its parent becomes a grandchild rather than a level-three item with no level two. That keeps the tree valid no matter how the source was pasted.

Does it export to Word or OPML?

Not to those formats. It produces indented markdown, a numbered outline and plain indented text, any of which you can copy or download and paste into a word processor to apply your own styles.

Do the numbers stay correct when I reorder items?

Yes. Numbering is computed from the tree each time the outline changes, never stored, so moving or re-indenting a line renumbers everything below it consistently.

Outline Builder

Outline

parsed locally

Numbering

Indented outline (two spaces per level; leading - bullets are optional)Tab or spaces both work

Shape

Items

deepest level: 3

Level 1

Level 2

Level 3

Depth: 3

Numbered outline

1. Introduction
  1.1 Background
    1.1.1 Prior work
  1.2 Thesis
2. Body
  2.1 Argument one
  2.2 Argument two
3. Conclusion

Indented markdown

- Introduction
  - Background
    - Prior work
  - Thesis
- Body
  - Argument one
  - Argument two
- Conclusion

Plain indented text

Introduction
  Background
    Prior work
  Thesis
Body
  Argument one
  Argument two
Conclusion

Scope and limits

Levels are read from indentation: a line indented by one unit is a child of the line above it, and an outline can only descend one level at a time, so a double-indented line becomes a grandchild rather than skipping to level three.

This is a structural helper, not a document generator: it does not decide what your sections should be and it does not export to DOCX or OPML. The report can be copied or downloaded as plain text; paste it into your word processor and apply your own styles.

The outline builder reads an indented outline into a tree and renders it back as indented markdown, a numbered outline (1. / 1.1 or I. / A. / 1.) and plain indented text for a word processor.

What is Outline Builder?

The outline builder does the small, fiddly job of turning a loose list of headings into a clean, numbered structure. You type the outline as indented lines — a section on one line, its subsections indented beneath it — and the tool reads the indentation into a tree, reports the shape, and writes it back out three ways: as indented markdown, as a numbered outline, and as plain indented text you can paste into a word processor.

Indentation is the whole interface, and the tool is forgiving about it. Leading dashes or numbers are optional, a tab counts as one level, and the parser normalises spacing so a pasted block with inconsistent indents still resolves. Crucially, an outline can only descend one level at a time: a line indented twice as deep as the line above it becomes a grandchild, not a line that skips a level and leaves the tree full of holes. That single rule is what keeps a hurried outline usable after the fact.

Numbering comes in two schemes. Decimal numbers give the familiar 1., 1.1, 1.1.1 pattern that reads well in technical documents and specs. The classic scheme gives I., A., 1., a., i., the traditional outline form for essays and reports. In both, the numbers are computed from the tree rather than stored, so reordering or re-indenting a line renumbers everything below it with no cleanup. Level counts sit beside the numbering, so you can see how deep the deepest branch runs.

The shape summary is deliberately plain: how many items the outline holds in total, how deep it goes, and how many items sit at each level. Those three numbers catch the two common mistakes — a section that has quietly become a buried sub-sub-subsection, and a branch that has one lonely child. Copy or download the rendering you need; the plain indented form drops the bullets and numbers so your word processor can apply its own heading styles.

The reverse direction matters too. Because the tool reads indentation, you can paste a rough outline from a notes app or a chat thread and get back a clean tree with sensible numbering, rather than retyping it indent by indent. It is equally useful at the end of an outline's life: the plain indented rendering, stripped of bullets and numbers, is the form a word processor wants when you apply heading styles, and the numbered rendering is the form a spec or a report wants when readers will refer to sections by number. Either way the structure you settled in the editor is carried through unchanged.

Everything runs in the browser, with no account, no upload and no storage beyond the tab. The builder is a structural helper, not a document generator: it does not decide what your sections should be, cannot infer an outline from a paragraph of prose, and does not export to DOCX or OPML. It reads indentation, counts the tree and formats the result, and it says so on the page. Because the three renderings are pure functions of the tree, moving a line changes every number below it consistently, which is exactly the discipline a hand-numbered outline punishes you for missing.

How to use Outline Builder

Type or paste the outline with one section per line, indented by two spaces per level.
Pick the numbering scheme: decimal 1. / 1.1, or classic I. / A. / 1. / a.
Read the shape summary to check the depth and the items at each level.
Copy the numbered outline, the markdown, or the plain indented text.
Download the report and paste the outline into your word processor.

When to use Outline Builder vs related tools

Use the outline builder when a document's structure is the thing you are deciding and you want it numbered without hand-editing. When you need to see how the outline has moved since the last draft, the Document Diff Viewer compares the two versions, and for a plain item tally the Word Count Tool is the lighter check.

Once the outline is settled and you are drafting, the Markdown Editor shows the same headings rendered with an outline of its own.

Privacy & Security

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.