Drawing and style

How pencilmark draws puzzles, and the conventions most sudoku software shares. None of this is part of a format: a sudoku-puzzle file says what each rule means, and a renderer may draw it any way that shows that meaning. The per-puzzle style and decorations keys (Puzzle format, section 7) carry a setter's own choices.

The line colours below are the community defaults, as measured on 6,217 published puzzles drawn in SudokuPad. All values, with a dark theme, are in palette.json; tools/render_svg.py is a reference renderer that follows this page.

A renderer needs nothing beyond the rules. Sizes are in cell units (1 = a cell's side); colours are defaults that style may override, and the Palette page shows every one in both themes. Grid lines 0.031, box borders and frame 0.07 (0.09 in the dark theme, where light lines on dark read thinner). Draw order, bottom to top: cell shading, lines, cage outlines, grid lines and box borders, edge / corner clues, digits, outside clues.

Rule	Default drawing
grid	Thin lines between existing cells only; nothing at null positions.
boxes (box_grid, box)	Thick line wherever two adjacent existing cells lie in different boxes, and around the outside of the existing cells.
rows / columns	Nothing beyond the grid lines.
region diagonal	Thin grey line through the cell centres, extended to the outer corners of the end cells.
region window / extra	Light grey shading (#d8d8d8).
region colour	Shading by a palette colour per rule, in rule order (#f4cccc #fce5cd #fff2cc #d9ead3 #d0e0e3 #c9daf8 #d9d2e9 #ead1dc #e6e6e6, repeating).
region disjoint / region	Nothing (listed in the legend).
cage	Dashed outline inset 0.08 from the cell edges; sum in small type (0.25) in the top-left corner of the first cell in reading order.
sum group	Like a cage, dotted.
sum corner	Small white circle (0.3) with the sum at the shared corner.
line thermo	Grey (#cccccc) line, width 0.3; filled bulb, diameter 0.75, at cells[0].
line slow_thermo	As thermo, bulb hollow.
line whisper	Green (#67f067), width 0.15; Dutch whisper (value 4) orange (#ffa600).
line renban	Pink (#f067f0), width 0.15.
line region_sum	Blue (#2ecbff), width 0.15.
line palindrome	Grey (#aaaaaa), width 0.15.
line entropic	Peach (#ffccaa), width 0.15.
line modular	Teal (#33bbaa), width 0.15.
line parity	Red (#ff6666), width 0.15.
line zipper	Lavender (#c8adeb), width 0.15, small dot at the centre.
line between	Grey line, width 0.1; hollow circles (0.75) at both ends.
line lockout	Grey line, width 0.05; hollow diamonds at both ends.
line double_arrow	Grey line, width 0.05; hollow circles at both ends.
closed lines	The segment from the last cell back to the first is drawn too.
arrow	Hollow circle (0.75) on a 1-cell bulb, rounded pill over a longer bulb; each shaft a thin grey line from the bulb's edge with an open arrowhead at its last cell.
edge kropki	Dot (0.25) at the midpoint: white with a black outline, or black.
edge xv	The letter X or V (height 0.3) on a white chip.
edge difference / sum / product / ratio	Small white circle (0.3) with the number; ratio shows k:1, product ×p.
edge greater	Chevron at the midpoint pointing at the smaller digit, cells[1].
corner battenburg	Small 2×2 checker square (0.3) at the corner.
corner mathrax	Small white circle at the corner with value and op (10+), or E / O.
corner exclude	Small white circle at the corner with the digit.
contains	On a 2×2 block: white circle (0.45) at the corner with the digits. Otherwise the digits in small type in the top-left corner of the first cell.
appears	A small arrow in the source cell pointing along cells.
sum little_killer	Small number outside cells[0] on side, with a short arrow pointing along cells[0] → cells[1].
sum frame, sandwich, skyscraper, first_seen, distinct_count with side	Plain number outside cells[0] on side. When kinds are mixed on one side: xsum in angle brackets ⟨n⟩, skyscraper in a small square, first_seen in a small circle.
xsum	Plain number outside cells[0] (⟨n⟩ when mixed).
rossini	Arrow glyph outside cells[0] on side, pointing into the grid (in) or out of it (out).
cell odd / even	Grey circle / grey square (0.8) behind the digit.
cell low / high	Light / dark grey diamond behind the digit.
cell set / exclude	The values in small type along the bottom of the cell; exclude struck through.
clone	The same light shading colour for all regions of one rule (palette as for colour regions).
vudoku	A grey right-angle corner: the elbow inside the vertex cell cells[0], near the corner the three cells share, the arms reaching into the arm cells. Cells that are not an L get a V through their centres.
equal_sum	Thin dashed outline around each segment.
isomorphic, count, global_entropy, neighbours, negative	Nothing in the grid (listed in the legend).
relation	Thin grey connector between the two cell centres.
Vendor rules	Light highlight of the cells plus the label text in the first cell.
givens	Large digit.
candidates	Small digits in a 3×3 keypad layout (centred for D > 9).