# sketch URL: https://tuios.dev/docs/libraries/sketch > Mermaid diagrams as SVG, PNG and box-drawing text, in pure Go. A port of pele by kepano. `tuios.dev/sketch` draws Mermaid diagrams in pure Go. It writes SVG, and its two packages turn a diagram into a picture (`sketch/raster`) or into box-drawing text for a terminal (`sketch/text`). It needs no browser, no JavaScript runtime and no cgo. ```bash go get tuios.dev/sketch ``` The API reference is on [pkg.go.dev](https://pkg.go.dev/tuios.dev/sketch). *[An interactive figure goes here. Open the page to use it.](https://tuios.dev/docs/libraries/sketch)* ## Credit sketch is a port of [pele](https://github.com/obsidianmd/pele), the Mermaid renderer by [kepano](https://github.com/kepano) of [Obsidian](https://obsidian.md/). pele is under the MIT licence, and so is the port. The port follows pele v1.6.0 (commit `458322a`). Each Go file is the port of one pele file and keeps its names and comments, so a change upstream maps to a change in sketch. The pele layout, the shapes, the themes and the timing of the typing demo are pele's work. The pictures use subsets of [Arimo](https://github.com/googlefonts/Arimo) (SIL Open Font License 1.1) and Go Mono. The licence notices are in `sketch/LICENSE` and `sketch/raster/fonts/NOTICE`. ## Diagram types | Type | pele's own SVG, byte for byte | | --------- | ----------------------------: | | flowchart | 114 of 114 | | sequence | 38 of 38 | | state | 22 of 22 | | class | 38 of 38 | | ER | 25 of 25 | | pie | 2 of 2 | | mindmap | 13 of 13 | | gantt | 11 of 11 | The test suite draws each source of the pele documentation corpus and compares the result with the SVG that pele drew from it. Every diagram of these eight types matches. Another type gives an error with the code `unsupported-diagram`. `sketch/text` draws flowcharts and sequence diagrams. ## Draw a diagram ```go svg, err := sketch.Render("flowchart LR\n A --> B\n", sketch.RenderOptions{}) if err != nil { // err is a *sketch.Error with a code: syntax, semantic, limit or unsupported-diagram. } os.WriteFile("out.svg", []byte(svg.Data), 0o644) ``` A picture: ```go th, _ := sketch.ThemeNamed("flexoki") img, err := raster.Draw(svg.Data, raster.Options{Scale: 2, Theme: th, Background: true}) ``` Text, for a terminal with no pictures: ```go d, _ := sketch.Parse(src, sketch.ParseOptions{}) lines, err := text.Draw(d, text.Options{Cols: 100}) ``` `text.ErrTooWide` says that the drawing does not fit in the columns. Before it gives up, the package asks for a narrower layout, which turns a flowchart that runs across into one that runs down. ## Themes pele takes its colours from the page. sketch keeps that in `--pele-*` tokens, and `sketch.Themes()` lists named sets of them: | Theme | From | | ----------------------------------------------------------------------------------------------- | --------------------------------- | | `pele` | pele's own colours | | `flexoki`, `flexoki-dark` | The pele.run site, light and dark | | `nord`, `everforest`, `gruvbox`, `rose-pine` | pele's launch video | | `catppuccin-mocha`, `catppuccin-latte`, `tokyo-night`, `dracula`, `solarized-light`, `kanagawa` | Those terminal themes | *[An interactive figure goes here. Open the page to use it.](https://tuios.dev/docs/libraries/sketch)* *[An interactive figure goes here. Open the page to use it.](https://tuios.dev/docs/libraries/sketch)* *[An interactive figure goes here. Open the page to use it.](https://tuios.dev/docs/libraries/sketch)* With `raster.Options.Readable`, text in a theme colour that sits on a fill the diagram sets itself changes to the theme's text or background colour, where that reads better. ## Limits The limits of pele apply. A source can have 50,000 characters, a flowchart 5,000 edges, and the SVG 4,000,000 characters. A host can set lower limits in `RenderOptions`. `sketch/raster` has its own pixel and work budgets, so hostile markup cannot run for long. Each package has fuzz targets. ## Speed Measured on one machine against pele under Node 24, warm, on the 152 flowchart and sequence sources of the corpus: the median render takes 21.8 µs in sketch and 43.6 µs in pele. A new process that draws one diagram takes about 2 ms with sketch and about 60 ms with pele. ## tuios mermaid *[An interactive figure goes here. Open the page to use it.](https://tuios.dev/docs/libraries/sketch)* `tuios mermaid` draws the Mermaid diagrams of a file with sketch. ```bash tuios mermaid flow.mmd # draw it here tuios mermaid README.md # every mermaid block of a Markdown file tuios mermaid flow.mmd -o flow.png # save a picture (or .svg) tuios mermaid flow.mmd --theme nord tuios mermaid flow.mmd --watch --split # draw again on every save, source beside it tuios mermaid --demo --theme flexoki # type a diagram, for a recording ``` - In a terminal with kitty graphics (kitty, Ghostty, or tuios on such a terminal), the diagram is a picture that fits the terminal. - In any other terminal, it is drawn with box-drawing characters, and the labels stay text. A type with no text drawing, or a drawing too wide for the terminal, is written as its source. - When the output is not a terminal, the command writes SVG. The colours come from your tuios theme by default. `--theme NAME`, or `theme` in the `[mermaid]` table, picks a named theme. `--watch` fills the terminal with the diagram and draws it again each time the file is saved. With kitty graphics, the diagram moves to its new layout: boxes slide and grow, new parts fade in and removed parts fade out. `--split` shows the source beside the diagram, or above it on a tall terminal. `--demo` types a diagram one character at a time: the diagram of FILE, or a built-in flowchart. Press r to start again and q to quit. The live view sends no frames while nothing moves. The [CLI reference](https://tuios.dev/docs/cli-reference#mermaid) lists every flag.