Ambigram Generator

How this works

A rotational ambigram reads correctly the right way up and again after a half turn. Turn the design and slot 1 lands where the last slot was, upside down, so slot i has to read as letter A[i] upright and as letter B[n-1-i] turned. For a single word, B is the same word.

Every letter is drawn as a few strokes on a small grid: 4 units wide, 8 tall, built from straight segments and quarter circles. The x-height band (where a, e, n, o and friends live) sits exactly in the middle, with the ascender zone above it and the descender zone below. That one decision does most of the work, because a 180 degree turn maps the grid onto itself and swaps ascenders for descenders. A d turned over lands on the p strokes exactly. So do b and q, n and u, m and a rounded w, h and a straight-tailed y, and a double-storey a and e.

For each slot the glyph is the union of the upright letter’s strokes and the turned strokes of the other letter. Where the two sets coincide, nothing extra is drawn. Where they do not, both letters’ strokes are drawn on top of each other and the reader has to pick out the one they want. Tick Show stroke sources to see which strokes belong to which reading.

How the score works

Each slot gets a score from 0 to 100%:

1. Overlap. Shared stroke length divided by total stroke length (a weighted Jaccard index). A stroke that only one reading needs is noise for the other, and it costs 1.5x if it cuts through the inside of the letter rather than running along its outline.
2. Confusion check. The finished glyph is compared against every letterform in the table. If it looks more like a different letter than the one intended, the slot is discounted by that margin and the verdict says what it may be misread as. This catches cases like an n whose partner adds an ascender, which overlaps well but reads as h.

The optimiser tries every allowed combination for each slot - lowercase and uppercase, plus alternates such as single- and double-storey a, plain and tailed l, pointed and rounded w, hooked and straight y - and keeps the best. In Auto mode it only switches away from the case you typed when that gains more than 3 points. Uppercase is drawn as small caps in the x-height band, so mixed cases share a baseline.

A short table of hand-designed glyphs covers pairs where the plain union is worse than a deliberate drawing: an r whose terminal stops at the midline so it can sit over a u without reading as n, and a centred stroke for l over l. Designed glyphs are scored with exactly the same metric and are only used when they score at least as well as the best union, so they never inflate a number.

Tiers: 75% and up is clean, 50 to 74% is readable, below 50% is weak. The overall number is the mean across slots.

Inputs explained

• Word A - reads upright. Letters a-z only, up to 16; accents are folded to the base letter and anything else is dropped.
• Word B - optional second word that appears when the design is turned. If the two lengths differ by one or two letters, the shorter word is padded with gaps. Every gap position is tried and the best-scoring one is kept; a padded slot shows its letter in one orientation only and scores zero, because in the other reading it is a stray mark. Larger differences are refused rather than faked.
• Case - Auto picks per slot; lower and UPPER force one case throughout.
• Style - Rounded draws true arcs with round caps; Sharp chamfers the corners and uses square caps. Scores are identical.
• Stroke weight and letter spacing - visual only, in SVG pixels.
• Colour and download background - design-token colours. Downloads embed the resolved colour values, so the file looks the same outside this site.

Examples that score well with this engine: swims (100%), NOON (100%), wow turning into mom (100%), dad into pep (100%) and dollop (83%, held back by the two l’s). For contrast, gekro manages 39%: k over k shares no strokes at all.

Limitations

• Some pairs are inherently weak. k over k, r over r, t over t and v over v share almost nothing once turned, and no amount of optimising fixes that. The tool tells you so instead of hiding it.
• The score measures stroke overlap, not beauty. It cannot see that a glyph is elegant, only that its strokes line up. A lettering artist drawing by hand will beat any algorithm, especially on the weak pairs, by bending letterforms in ways a fixed grid cannot.
• One glyph style. Everything is built from one geometric segment alphabet. Script, serif and blackletter ambigrams are out of scope.
• Rotational only. Mirror (reflection) ambigrams, chain ambigrams and figure-ground designs are different problems.
• Letters only. Digits, punctuation and spaces are not drawn.

Everything runs locally in your browser. No word you type is uploaded, and the SVG and PNG files are built on your device.