Cheatsheet: Graphviz

dot is the default and best for directed graphs with a clear hierarchy (trees, flowcharts, dependency graphs) -- it lays nodes out in ranks. neato and fdp use force-directed (spring-model) layouts that work better for undirected graphs without a natural hierarchy, like network diagrams; fdp is faster on large graphs. circo arranges nodes in a circular layout, useful for showing cyclic structures. twopi produces a radial layout from a chosen root node. Pick the engine with -K<engine> on the command line or by setting layout=<engine> in the graph.

Use the -T flag with the dot CLI: dot -Tpng graph.dot -o graph.png, dot -Tsvg graph.dot -o graph.svg, or dot -Tpdf graph.dot -o graph.pdf. SVG is usually the best choice for the web since it stays crisp at any zoom level and lets you inspect/edit the markup directly; PNG is fine for a fixed-size raster embed.

A subgraph is only rendered as a bordered cluster if its name starts with the literal prefix cluster_ (e.g. subgraph cluster_backend { ... }) -- any other name is just a grouping construct with no visual box. Inside the cluster you also need at least one style attribute (like style=filled or style=rounded) plus a color for the border/fill to actually show up, and a label if you want a cluster title.

Set splines on the graph: splines=ortho draws edges as right-angle (orthogonal) lines, splines=curved or splines=spline draws smooth curved paths that route around nodes, and splines=polyline draws straight-segment paths. splines=line/false disables curve fitting and can produce cleaner results on dense graphs at the cost of edges crossing through node boxes more often -- pair it with more nodesep/ranksep spacing if that happens.

By default DOT treats repeated edges (like A -> B declared twice) as distinct parallel edges and draws both. Wrap the whole graph in strict mode (strict digraph G { ... } or strict graph G { ... }) to automatically merge duplicate edges into one -- note strict also merges same-endpoint edges even if they have different attributes, keeping only the first declaration's attributes.