Straight Arrows

Straight arrows are the workhorse annotation for pointing at structures, labeling steps, and marking simple relationships. You draw them with a single drag, adjust either endpoint afterward, and optionally anchor an endpoint to an atom, bond, or another annotation so the arrow follows its target. This page covers the straight variants only. Curved arrows, mechanism arrows, and shape cleanup have their own pages.

Picking an arrow variant

Click the arrow button in the toolbar to open its flyout. The straight variants are:

Straight Arrow: plain shaft with a filled head at the end
Double-headed: filled heads on both ends
Harpoon Up and Harpoon Down: single-barbed heads, used in pairs for equilibria or radical chemistry

The same flyout also holds curved, reaction, equilibrium, and retrosynthesis arrows; see the linked pages for those.

Press A to activate the arrow tool from the keyboard. While the tool is active, number keys switch variants: 1 straight, 2 double-headed, 4 harpoon up, 5 harpoon down.

Drawing

With the arrow tool active, press down where the arrow should start and drag to where it should end. Release to place the arrow. A short click without a drag places a default-length arrow. After the arrow is placed, Molkit switches back to the Select tool; hold Alt while releasing to stay in the arrow tool and draw several arrows in a row.

Angle snapping

While you drag, the arrow snaps to 15 degree angle increments. Hold Shift to draw at a free angle. Shift also suppresses snapping to nearby attach targets, so use it whenever the arrow keeps grabbing something you do not want.

Adjusting endpoints

Select an arrow with the Select tool and white square handles appear at both endpoints. Drag a handle to move that endpoint; the other end stays put. Endpoint drags snap to 15 degree increments by default; hold Shift to constrain to 45 degree increments instead, or Alt to drag at a free angle.

Anchoring endpoints

Arrows anchor to nearby targets as you draw them with the arrow tool. To attach or re-attach an endpoint afterward, hold Ctrl while dragging it (see below). Anchored endpoints track their target: move the molecule and the arrow follows. Targets include, in priority order: lone pairs, radicals, bond midpoints, annotation edges, and atoms. While you draw near a target, the candidate highlights with a dashed ring, and small dots mark the available anchor points on nearby atom labels.

An anchored endpoint shows a small accent-colored dot inside its white square handle, so you can tell pinned from free endpoints at a glance.

Adjust the standoff gap: drag the anchored endpoint’s white square to slide the tip toward or away from its target. While you drag, a readout near the cursor shows the current contact position and gap. The Shape Properties panel also has Gap 1 and Gap 2 sliders (0 to 10 px) for precise values. The panel’s Anchor section adds Start and End position sliders (0 to 100% along the attached bond or label edge) and, for edge attachments, head-angle sliders.
Attach or re-anchor: hold Ctrl while dragging any endpoint to snap it onto a target (or move it from its current target to a different one). Dropping it in empty space clears the anchor entirely.

Cycling arrowhead styles

Press H to cycle the end arrowhead through filled, harpoon up, harpoon down, and back to filled. It applies to all selected arrows, or to the arrow tool’s current setting when nothing is selected.

The H cycle covers the three common styles; the full set lives in the Shape Properties Panel, which offers 12 head styles per end (None, Filled, Stealth, two harpoon families, Diamond, Rotated Square, Circle, Square, and Open) plus head size sliders and a sharp-points option.

Color and width

Select an arrow and open the Shape Properties panel on the right. Stroke color, opacity, and stroke width live there, along with head size controls and the Anchor gap sliders described above.