zbCAD Documentation

zbCAD is a 2D drafting tool modeled on the drawing conventions common to desktop CAD software: a typed command line that accepts abbreviations, keyboard shortcuts, and coordinate expressions like @3,2 or @5<45; object snap to precisely pick existing geometry; layers; and associative dimensions that stay attached to the geometry they measure. If you've used a traditional desktop CAD package before, most of this will already feel familiar.

Everything lives in your browser tab. Drawings are saved to a local .zbCAD.json file you download and re-open yourself, and an autosave copy is kept in the browser's own storage so an accidental tab close doesn't lose your work.

Your drawings never leave your computer. Nothing you draw or open is uploaded — there's no server to send it to, and everything the app does happens in your browser tab, using the files you open and the browser's own storage. The one thing the page sends is a visit count to GoatCounter, which records that the page was opened and nothing that's in it.

zbCAD is built for a mouse and keyboard on a wide display; it has no touch input handling or small-viewport layout. A narrow window or a touch device shows a dismissible warning to that effect rather than silently breaking — Continue anyway skips it for anyone who wants to try regardless.

A first drawing, from a blank page to a PDF at scale. Type the commands straight in: whatever you type goes to the command line at the bottom, and Enter runs it.

1. Draw a rectangle. Type REC and press Enter. Type 0,0 Enter for one corner, then @40',25' Enter for the other. That's a 40' × 25' rectangle; @ means “from the last point”.
2. Bring it into view. Click Zoom Extents to fit the drawing to the window. Scroll to zoom and middle-drag to pan from there.
3. Set the drawing scale. Type DST, set Drawing scale to 1/4" = 1'-0", and press Apply. Dimension text and ticks are sized for paper, and this sets how big they come out in the drawing. Without it, dimension text on a building-sized drawing is too small to see.
4. Dimension it. Type DLI, click the rectangle's bottom-left and bottom-right corners (the snap marker shows when you're on one), then click a little below the rectangle to place the dimension. Typing 0,0, 40',0 and 20',-6' does the same. It reads 40'-0" and stays attached to the corners if they move.
5. Save. Ctrl+S downloads the drawing as a .zbCAD.json file. It's also autosaved in the browser as you work.
6. Plot. Ctrl+P opens Plot to PDF. Pick a sheet size, set Scale to Exact scale and Drawing scale to 1/4" = 1'-0", check the preview, and press Plot for a PDF that measures true at that scale.

From here, the command line and object snap are the two things worth reading first.

The window is divided into a few fixed regions:

• Toolbar (top) — the File, Edit, View, and Inquiry groups sit in the always-visible top row beside the zbCAD logo; Select, Draw, Modify, and Annotate follow it, wrapping onto further rows as the window narrows. Buttons that start a command show its keyboard alias in parentheses, e.g. Line (L). The Auto-hide button next to the logo collapses those drawing groups away, freeing up canvas height; mouse over the bar (or Tab into it) to bring them back as an overlay without resizing the canvas underneath it. File, Edit, View, and Inquiry stay put either way, so opening a drawing or undoing never needs the overlay. This preference is remembered per browser.
• Canvas (center) — the drawing area. Left-click to pick points or select objects, scroll to zoom, middle-drag to pan, right-click or Enter to accept the current command's default action.
• Side panel (right) — a Properties section on top for editing the current selection, and a Layers section below listing every layer with its visibility, lock, and color controls, plus its linetype, lineweight, and printable toggle. Each section collapses independently with the ▸ / ◂ toggle on its own heading (an accordion within the panel). The whole panel can be resized by dragging the handle on its left edge, or collapsed entirely by clicking the handle; both the width and collapsed state are remembered per browser.
• Command line & status bar (bottom) — the text input where you type commands, coordinates, and keywords, plus toggle buttons for SNAP, ORTHO, POLAR, the active object-snap set, the drawing units, the current file name, and the live cursor coordinates.
• Inquiry panel — a small overlay that appears with the result of DIST, AREA, ID, or LIST; close it with the × button or Esc.

The command line

Click a toolbar button, or click the command-line input and type a command name (or its alias, e.g. L for LINE) and press Enter or Space. You don't need to click into the input first — typing any single character while the canvas has focus jumps into the command line automatically.

While a command is running, the same input accepts, in order of precedence:

1. A keyword the active command is listening for (its prompt tells you which letters are live, e.g. C to close a polyline, U to undo the last point).
2. A point, typed as x,y, @x,y (relative to the last point), or @distance<angle (polar, relative).
3. A command-specific value (an angle for ROTATE, a scale factor for SCALE, etc.).
4. A bare distance, applied along the direction from the last point toward the current cursor position — type a number right after picking a start point and dragging toward a direction to draw an exact length without doing the trigonometry yourself.

An unrecognized string that matches none of the above is looked up as a new command name.

Entering points & distances

A leading - negates a distance; a leading + is accepted and ignored.

Object snap

With SNAP on (the default), moving the cursor near existing geometry pulls the pick point onto a precise feature of it — essential for drawing connected geometry instead of eyeballing it. Click the snap-type readout in the status bar (next to the SNAP toggle) to choose which snap types are active:

When several snap points coincide on screen, the one listed first above wins, rather than whichever happens to be a pixel closer.

A polyline's curved segment counts as an arc for every snap above: its center, quadrants and tangent points are live, Midpoint lands halfway along the arc, and Nearest follows the curve rather than the straight chord across it.

Ortho & polar tracking

ORTHO (F8) constrains the next point to be exactly horizontal or vertical from the current base point. POLAR (F10) instead locks onto the nearest multiple of a chosen angle increment (45° by default — change it via the polar readout in the status bar) whenever the cursor comes close to that alignment ray; move further off the ray and the lock releases. The two are mutually exclusive — ORTHO is really polar tracking at a fixed 90° increment, so turning one on turns the other off. Both only apply to commands that opt into tracked point entry (drawing and most modify commands); commands that ask you to pick a location rather than a measured point (e.g. which side of a line to keep when trimming) ignore both.

Selection & grips

With no command running, click an object to select it, or drag a box: dragging left-to-right selects only objects fully enclosed by the box, dragging right-to-left selects anything the box touches. Hold Shift to add to the current selection instead of replacing it. Delete erases the current selection. Commands that operate on a selection (MOVE, COPY, ERASE, ...) use the same picking and box-selection behavior at their "select objects" prompt.

Selected objects show small square grips at their defining points (endpoints, center, etc.). Click and drag a grip to reshape or reposition that point directly, without starting a command; click a grip without dragging to leave the edit live and then type or pick a destination point.

The Properties section of the side panel reflects whatever is currently selected: a layer dropdown (change it to reassign every selected object, and images, to that layer at once), and, when the selection is a single entity type, editable fields for that type's plain scalar properties — radius for CIRCLE/ARC, height/rotation for TEXT, height/width/rotation for MTEXT, plus the text content itself for TEXT and MTEXT. A mixed selection just shows the summary and the layer field; geometry that would need reshaping a whole entity (line endpoints, polyline vertices) stays grip-only. Editing a field applies it to every selected entity of that type at once.

Layers

Every object lives on exactly one layer. The layers panel lists each with a radio-style "make current" marker, an editable name, a color swatch, a visibility toggle, a lock toggle, and a delete button, over a second row carrying the layer's linetype, lineweight, and printable toggle. New objects are drawn onto the current layer, chosen from the dropdown above the panel or by clicking a layer's marker. Locked layers can't be edited; hidden layers don't render and aren't picked by selection or snap.

Assign selection to current moves the selected objects onto whichever layer is current. Layer 0 can't be renamed or deleted, and the current layer can't be deleted while it's current.

A layer also carries three properties that decide how its objects are drawn rather than which of them exist:

Both linetype and lineweight are layer properties only; there is no per-object override. Drawings saved before these existed open as continuous, 0.25 mm, printable layers and look exactly as they did.

Units & dimension style

Open Units (UN) to set the drawing's physical unit (inches, feet, millimeters, centimeters, meters) and how lengths are displayed:

The units dialog offers to rescale existing geometry when you change the drawing unit, so switching from inches to millimeters mid-drawing doesn't silently change what your geometry means.

Dim Style (DST) controls how dimension objects are drawn: arrowhead style (tick or arrow), overall scale, text height, arrow size, and text precision (or "follow the document" to always match the current unit precision). New drawings default to arrows in metric units and ticks otherwise, matching common drafting convention.

Files & autosave

Save downloads the current drawing as a <name>.zbCAD.json file through the browser's normal download mechanism. Open loads a .zbCAD.json file back in. New clears the canvas (with a confirmation if it isn't already empty).

Every change is also autosaved into the browser's own database (IndexedDB, or ordinary local storage where the browser doesn't allow a database) after a short delay, and the previous autosave is kept as a backup slot. Closing the tab during that delay writes one last snapshot on the way out, so what you're offered back is the drawing you actually last had. If a drawing is still open in browser storage when you return — a crash, an accidental tab close, forgetting to Save — zbCAD offers to recover it. Recover Backup in the toolbar explicitly restores the older, previously-autosaved slot (rather than the most recent one) if you need to step back one version, and replaces the current drawing when used, so Save first if you want to keep a copy of what's currently open.

Autosave and manual Save are a convenience, not a substitute for keeping your own backups — both live only in this browser's storage or wherever you chose to save the downloaded file.

Plotting to PDF

Plot (PLT) writes the drawing to a PDF as real vector geometry — not a screenshot of the canvas. Lines stay lines, so the sheet can be measured, marked up, and printed at any resolution. Ctrl/Cmd+P opens the same dialog.

The dialog previews the sheet live as sheet size, area and scale are chosen, drawn from the same plot plan the PDF is serialised from, so there is nothing between choosing options and seeing what lands on paper. Anything that falls outside the printable border is shown in amber rather than left off the preview, since a line half on the sheet and half clipped is exactly the mistake this is meant to catch before the file is written. Text too small to read at preview scale is greeked into a bar instead of vanishing — annotation that is really on the sheet shouldn't look absent in the picture of it. The dialog widens to two columns to fit the preview, collapsing back to one on a narrow window.

Sheet size offers the ANSI, ARCH and ISO sizes, in either orientation, with a half-inch margin the plot is fitted inside and clipped to. Plot area is the drawing extents, the current view, or a rectangle you pick on the drawing with Pick window (the dialog steps aside for the two corners and comes back with the window filled in).

Scale is the part that has to be exact. Fit to the sheet works out whatever scale makes the plot area fill the page; Exact scale takes a drawing scale — 1/4" = 1'-0", 1" = 20', 1:100 — and plots at precisely that, so a hundred-foot wall at 1" = 20' measures five inches on the sheet. If an exact scale is too large for the sheet the plot still runs, clipped at the margin, and says so before you commit to it.

Color plots monochrome by default: layer colors are chosen to read on the dark drawing area and several of them are nearly invisible on white paper. Plot layer lineweights uses each layer's millimetre lineweight; turned off, everything plots thin. Objects on hidden layers and on layers marked non-printable are left off the sheet entirely — that is what the layer panel's printable toggle is for.

Images & underlays

Image places a raster image — a scan, a photo, an exported PDF page — as an underlay to trace over. Pick a file, then either click a bottom-left corner to place it at a provisional scale of one drawing unit per pixel, or type a width first to place it at that width instead. The image is re-encoded to JPEG and capped at 2400px on the long side on import, which keeps it small enough to travel inline in the saved drawing and every autosave.

An image imported this way carries no real-world scale until you set one. Calibrate does that: click two points on the image a known distance apart, then type (or click to measure) that true distance, and the image is rescaled about the first point so the second lands exactly that far away. Recalibrating is not a one-time step — do it again whenever a better-known dimension turns up.

PDF places a page of a PDF the same way, with two differences that come from what a PDF is. First, a drawing that was plotted or exported from CAD is line work, and it is kept as line work: the page stays sharp however far you zoom in, and object snap finds the ends, midpoints and crossings of its lines, so what you trace lands exactly on the original rather than near it. Second, a PDF knows the size of its sheet, so the page comes in at true paper size and the number to type before placing it is the scale the sheet was drawn at — 48, 1:100 or 1/4"=1' (no spaces) — after which the building is full size and nothing needs calibrating. A file with several pages asks which one first, and stays open afterwards: type PDF again to place the next sheet of the same set.

The page is shown in its own colours turned over for the dark drawing area — black ink draws white, coloured lines keep their colour — and plots in the colours it came with. Its text is real text, in the right place at the right size, set in a stand-in typeface stretched to the width the original occupied; the fonts themselves are not read, so lettering will not look identical. Pictures on the page (logos, shaded views, photographs) are left out, as are pattern and gradient fills, and the prompt says how many when it places the page. A page that is nothing but a scan comes in as an image instead, and is then subject to the same 2400px cap as any other image; a scan stored as fax-compressed black and white (CCITT or JBIG2, the usual output of a large-format scanner) cannot be read and has to be saved as a PNG or JPEG first. Password-protected PDFs are refused.

An underlay lives on a layer like any other object, so its visibility, lock, and printable state come from the ordinary layer controls rather than a separate system — hide, lock, or leave a traced-over image off the plotted sheet the same way you would a layer of construction lines. A printable underlay's image does appear on a plotted PDF, not just on screen. Selecting an image shows fade, lock and layer controls in the Image Props dialog (also opened by the UNDERLAY command); it also participates in MOVE, COPY, ROTATE, SCALE, MIRROR and ERASE like any selected object, and shows up in the Properties panel's selection summary.

DXF import & export

Import DXF (DXFIN) and Export DXF (DXFOUT) read and write the AutoCAD DXF format (R2000/AC1015 ASCII), for moving drawings to and from other CAD software. Importing replaces the current drawing rather than inserting into it — save first if you want to keep what's currently open. The drawing's unit is read from (and written to) the file's $INSUNITS header, so geometry round-trips at the same real-world size.

Export writes real ARCs, symbolic layer names (with their color, linetype, lineweight and printable state), and live DIMENSION entities — not lines standing in for them — so a dimension opened in another application still reads as a dimension. Import understands both the older R12 POLYLINE/VERTEX form and the modern LWPOLYLINE, and flattens block references (INSERT), including nested and arrayed ones, into plain geometry. Ellipses and splines have no exact zbCAD equivalent and are approximated; angular and ordinate dimensions likewise have no matching zbCAD entity, so their block geometry is imported as exploded lines rather than a live dimension. Every skip or approximation made during import is reported to the inquiry panel rather than happening silently.

Image underlays have no DXF equivalent (that would need a separate IMAGEDEF reference to an external file) and are left out of an export, which warns that it did so rather than silently dropping them.

Draw

Modify

Transform

Annotate

Inquiry

Inquiry commands are read-only: they never modify the drawing or create an undo entry.

Other commands