The Pen Tool
Every path in Illustrator can be drawn with the Pen tool. It is worth learning correctly, because it is the most precise drawing instrument in the application.
Why this matters
The Pen tool is how you draw precisely in Illustrator. Unlike the Pencil or Brush tools, which follow the movement of your cursor, the Pen tool places anchor points deliberately and defines path segments between them. It is the tool for constructing accurate diagram boundaries, custom diagram symbols, annotation shapes, and any path that needs to follow specific geometry rather than free-form gesture.
How the Pen tool works
| Action | How to do it | What it produces |
|---|---|---|
| Place a corner anchor point | Click (do not drag) | A sharp corner — the path changes direction abruptly at this point |
| Place a smooth anchor point | Click and drag in the direction of the next curve | A smooth anchor with direction handles — the path curves through this point |
| Close a path | Click on the first anchor point | Connects the last point to the first, completing the closed shape |
| End an open path | Click on the last point while holding Alt, or press Escape | Ends the path without closing it |
| Continue an existing open path | Click the endpoint of the open path with the Pen tool active | Picks up from the endpoint and continues drawing |
| Add an anchor point to an existing path | Click on the path between existing anchor points | Adds a point without changing the path shape — for subsequent editing |
| Remove an anchor point | Click on an existing anchor point with the Pen tool | Removes the point and attempts to maintain the surrounding path shape |
| Convert a corner to smooth (or vice versa) | Alt+click an anchor point | Toggles between corner and smooth anchor types |
Pen tool modifiers
The Pen tool family includes four related tools accessible by holding the Pen tool icon in the toolbar:
| Tool | Keyboard | Use |
|---|---|---|
| Add Anchor Point | + (plus) | Add a point to any existing path |
| Delete Anchor Point | – (minus) | Remove a point from any existing path |
| Anchor Point | Shift+C | Convert between smooth and corner anchors, adjust direction handles |
| Curvature tool | Shift+˜ | Simplified curve drawing — less control than the Pen tool but faster for organic shapes |
Editing paths after drawing
Use the Direct Selection tool (A) — the white arrow — to select and move individual anchor points or segments after a path is drawn. The black arrow (Selection tool, V) selects the entire object. The white arrow edits its geometry. This distinction is critical — selecting a path with the black arrow and pressing Delete removes the whole object; selecting a point with the white arrow and pressing Delete removes only that point.
To move a path segment without moving its anchor points, use the Direct Selection tool to click on the segment (not a point) and drag.
Snapping in Illustrator
Illustrator has smart guides and snap-to-point capabilities that function similarly to AutoCAD's OSNAP. Enable them via View → Snap to Point and View → Smart Guides. With smart guides active, the cursor will snap to anchor points, path midpoints, and geometric relationships as you draw. This is essential for accurate diagram construction — connecting paths at shared boundaries, aligning diagram areas to the base plan, and building geometry that relates correctly to the imported CAD reference.
Try this
Draw a closed irregular shape with at least two straight edges and two curved edges using only the Pen tool — no shape tools. Close it precisely on the first anchor point. Then use the Direct Selection tool to adjust two anchor points and one direction handle. Then add an anchor point mid-segment and convert it from corner to smooth. This sequence covers every Pen tool operation you'll use in diagram construction.
What breaks
Dragging when you meant to click — accidentally dragging while placing an anchor point creates unwanted direction handles, producing curves where you wanted corners. If this happens, immediately undo (Cmd/Ctrl+Z) and re-click without dragging.
Not closing paths before filling — an unfilled open path looks similar to a closed one on screen, but it will fill incorrectly (Illustrator invents an edge between endpoints). Always close paths that are intended to be filled areas using the close-path click on the first anchor.