Download for Windows · Specification · How it works · Decoder and test results

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What Heptapod L is

Heptapod L began with the circular writing of the heptapods in the film Arrival (2016) and went further. The film gives us an image: ink rings with organic tendrils, one ring per thought. It does not give us an alphabet. Heptapod L is an original writing system that keeps that look and adds what the film never provided:

• An alphabet. 26 letters, each a distinct tendril shape, plus digits, punctuation and an escape for any Unicode character.
• A grammar of position. The first unit of a sentence fixes where its logogram starts on the circle. Everything else follows clockwise.
• Compression. Letters fuse into two-letter dicasts and three-letter tricasts, with 18,278 distinct letter units in all, so sentences use fewer marks.
• Full reversibility. Every logogram can be read back to the exact text, from the drawing itself.

Heptapod L is a fan-inspired, independent project. It is not affiliated with or endorsed by the makers of Arrival and does not reproduce the film's glyphs.

The script in eight ideas

#	Idea	In one line
1	Tricast first	Letters are grouped three at a time (then two, then one): HUMANITY → HUM · ANI · TY. That's 3 units instead of 8 and a ring about 25% shorter.
2	Angled starts	The first unit sets the sentence's orientation: LARRY starts at 152.656° because it opens with the tricast LAR.
3	One glyph, four features	Every letter is a tendril defined by direction, curl, barbs and length. That gives 36 shapes, 26 of which are letters.
4	Five unit types	Letter, dicast, tricast, special (digits and punctuation) and escape (any other character).
5	Spacing and boundaries	Fixed gaps inside units, wider gaps between units, a short bar between words and a long bar at the start.
6	One sentence, one logogram	Long sentences continue on further rings outward.
7	Two layers of ink	The strokes carry the meaning; the pigment around them is decoration that a reader can strip away.
8	Read it back	Exact decoding from SVG, and shape-matching decoding from PNG or JPEG images.

Each idea is explained with examples in docs/HOW-IT-WORKS.md. The exact rules are in docs/SPECIFICATION.md.

Heptapod L Studio

The Studio is a local web application served by Windows PowerShell at http://localhost:8765/. It has three panels:

• Language input: type any text and see how it is normalised and segmented, plus a basic reading of its meaning (statement or question, intent, roles).
• Logogram output: the rendered logogram, its origin angle and a table of every unit. Each render is checked by decoding it again, both from the SVG and from its pixels. Export as SVG or PNG, in white-on-night or black-on-paper ink.
• Interpreter / decoder: drop in an SVG, PNG or JPEG. The Studio overlays what it detected (ring, start, units) and returns the text with a confidence score, or tells you it cannot read the image. It never guesses.

There is also a glyph lookup, an orthography reference and self-tests that run in the background.

Everything runs locally. There are no cloud services, no AI and no internet access at run time.

Install (Windows 10/11)

Option 1: setup program (recommended). Download HeptapodL-Setup.exe from the latest release and run it.

• It installs for your Windows account only, so no administrator rights are needed.
• It starts the Studio automatically at sign-in and opens it in your browser.
• It places the three infographics on your Desktop.
• It adds a Start-menu entry and an uninstaller in Settings → Apps.

The setup program is not code-signed, so Windows SmartScreen may warn on first run: choose More info → Run anyway.

Option 2: ZIP. Download HeptapodL-Package.zip, extract it and double-click Install.cmd. Use this if your organisation blocks unsigned programs.

Option 3: one script. Copy the contents of installer/HeptapodL-Install.ps1 and paste it into Windows PowerShell 5.1.

All three run the same verified install:

1. Back up any previous version.
2. Free port 8765, but only if the previous Studio holds it; the installer never stops other software or changes the port.
3. Write the files.
4. Compile the image decoder.
5. Start the server, then encode, decode and run a self-test.

If any step fails, the installer restores the previous version and reports why.

Infographics

	How the Script Works: the eight core ideas, with real renders and measured figures.
	Positional Map (night): all 26 letters, dicast and tricast samples, the full positional circle and the 36-symbol special register.
	Positional Map (paper): the letter, dicast and tricast registers with worked example positions and the special register.

Every symbol on these sheets is drawn by the Heptapod L engine itself; none is illustrated by hand.

How well it reads back

Test	Result
Every letter, dicast and tricast (18,278 units) plus all 36 specials, decoded from SVG	18,313 / 18,313 exact
100 random sentences rendered by Chrome, exported as PNG and JPEG at 0.7×, 1× and 2× in both ink styles, decoded from pixels	96 / 100 exact; all 4 misses were flagged as uncertain, with no confident wrong answers
Screenshots of the Studio page in both ink styles	Decoded
Images that are not Heptapod L (including AI-generated "heptapod" art)	Refused with an explanation

Details and method: docs/DECODER.md.

Repository layout

src/server.ps1          Engine, composer, SVG decoder, HTTP server (Windows PowerShell 5.1)
src/hsraster.cs         Image (PNG/JPEG) decoder, C# 5, compiled locally by PowerShell at start-up
src/index.html          Studio interface
installer/              Paste-in installer, Windows setup script (NSIS), ZIP launcher, uninstaller, icon
infographics/           The three infographics
docs/                   Specification, explanations, decoder notes, images

To build the setup program yourself: makensis installer/heptapodl.nsi, with the infographics and Install.ps1 placed next to it as listed in the script.

Limitations

• The Studio reads only logograms that Heptapod L itself produced. It does not translate hand-drawn or film heptapod writing, and it says so rather than inventing text.
• Image decoding becomes less reliable below about 500 px across. Use the SVG export for exact results.
• The meaning reading is rule-based and basic; the spelling, which is fully reversible, is the authoritative layer.
• Text is normalised to capitals.

Author

Heptapod L was created by Larry Dalton. © 2026 Larry Dalton. All rights reserved.