Dagre is a JavaScript library for laying out directed graphs. It computes optimal node positions for hierarchical/tree layouts. React Flow handles rendering; dagre handles positioning.

Quick Start

pnpm add @dagrejs/dagre

import dagre from '@dagrejs/dagre';
import { Node, Edge } from '@xyflow/react';
const getLayoutedElements = (
  nodes: Node[],
  edges: Edge[],
  direction: 'TB' | 'LR' = 'TB'
) => {
  const g = new dagre.graphlib.Graph();
  g.setGraph({ rankdir: direction });
  g.setDefaultEdgeLabel(() => ({}));
  nodes.forEach((node) => {
    g.setNode(node.id, { width: 172, height: 36 });
  });
  edges.forEach((edge) => {
    g.setEdge(edge.source, edge.target);
  });
  dagre.layout(g);
  const layoutedNodes = nodes.map((node) => {
    const pos = g.node(node.id);
    return {
      ...node,
      position: { x: pos.x - 86, y: pos.y - 18 }, // Center to top-left
    };
  });
  return { nodes: layoutedNodes, edges };
};

Core Concepts

Coordinate System Difference

Critical: Dagre returns center coordinates; React Flow uses top-left.

// Dagre output: center of node
const dagrePos = g.node(nodeId); // { x: 100, y: 50 } = center
// React Flow expects: top-left corner
const rfPosition = {
  x: dagrePos.x - nodeWidth / 2,
  y: dagrePos.y - nodeHeight / 2,
};

Node Dimensions

Dagre requires explicit dimensions. Three approaches:

1. Fixed dimensions (simplest):

g.setNode(node.id, { width: 172, height: 36 });

2. Per-node dimensions from data:

g.setNode(node.id, {
  width: node.data.width ?? 172,
  height: node.data.height ?? 36,
});

3. Measured dimensions (most accurate):

// After React Flow measures nodes
g.setNode(node.id, {
  width: node.measured?.width ?? 172,
  height: node.measured?.height ?? 36,
});

Layout Directions

g.setGraph({ rankdir: 'LR' }); // Horizontal layout

Complete Implementation

Basic Layout Function

import dagre from '@dagrejs/dagre';
import type { Node, Edge } from '@xyflow/react';
interface LayoutOptions {
  direction?: 'TB' | 'BT' | 'LR' | 'RL';
  nodeWidth?: number;
  nodeHeight?: number;
  nodesep?: number;  // Horizontal spacing
  ranksep?: number;  // Vertical spacing (between ranks)
}
export function getLayoutedElements(
  nodes: Node[],
  edges: Edge[],
  options: LayoutOptions = {}
): { nodes: Node[]; edges: Edge[] } {
  const {
    direction = 'TB',
    nodeWidth = 172,
    nodeHeight = 36,
    nodesep = 50,
    ranksep = 50,
  } = options;
  const g = new dagre.graphlib.Graph();
  g.setGraph({ rankdir: direction, nodesep, ranksep });
  g.setDefaultEdgeLabel(() => ({}));
  nodes.forEach((node) => {
    const width = node.measured?.width ?? nodeWidth;
    const height = node.measured?.height ?? nodeHeight;
    g.setNode(node.id, { width, height });
  });
  edges.forEach((edge) => {
    g.setEdge(edge.source, edge.target);
  });
  dagre.layout(g);
  const layoutedNodes = nodes.map((node) => {
    const pos = g.node(node.id);
    const width = node.measured?.width ?? nodeWidth;
    const height = node.measured?.height ?? nodeHeight;
    return {
      ...node,
      position: {
        x: pos.x - width / 2,
        y: pos.y - height / 2,
      },
    };
  });
  return { nodes: layoutedNodes, edges };
}

React Flow Integration

import { useCallback } from 'react';
import {
  ReactFlow,
  useNodesState,
  useEdgesState,
  useReactFlow,
  ReactFlowProvider,
} from '@xyflow/react';
import { getLayoutedElements } from './layout';
const initialNodes = [
  { id: '1', data: { label: 'Start' }, position: { x: 0, y: 0 } },
  { id: '2', data: { label: 'Process' }, position: { x: 0, y: 0 } },
  { id: '3', data: { label: 'End' }, position: { x: 0, y: 0 } },
];
const initialEdges = [
  { id: 'e1-2', source: '1', target: '2' },
  { id: 'e2-3', source: '2', target: '3' },
];
// Apply initial layout
const { nodes: layoutedNodes, edges: layoutedEdges } = getLayoutedElements(
  initialNodes,
  initialEdges,
  { direction: 'TB' }
);
function Flow() {
  const [nodes, setNodes, onNodesChange] = useNodesState(layoutedNodes);
  const [edges, setEdges, onEdgesChange] = useEdgesState(layoutedEdges);
  const { fitView } = useReactFlow();
  const onLayout = useCallback((direction: 'TB' | 'LR') => {
    const { nodes: newNodes, edges: newEdges } = getLayoutedElements(
      nodes,
      edges,
      { direction }
    );
    setNodes([...newNodes]);
    setEdges([...newEdges]);
    // Fit view after layout with animation
    window.requestAnimationFrame(() => {
      fitView({ duration: 300 });
    });
  }, [nodes, edges, setNodes, setEdges, fitView]);
  return (
    

      

         onLayout('TB')}>Vertical
         onLayout('LR')}>Horizontal
      
      
    
  );
}
export default function App() {
  return (
    
      
    
  );
}

useAutoLayout Hook

Reusable hook for automatic layout:

import { useCallback, useEffect, useRef } from 'react';
import {
  useReactFlow,
  useNodesInitialized,
  type Node,
  type Edge,
} from '@xyflow/react';
import dagre from '@dagrejs/dagre';
interface UseAutoLayoutOptions {
  direction?: 'TB' | 'BT' | 'LR' | 'RL';
  nodesep?: number;
  ranksep?: number;
}
export function useAutoLayout(options: UseAutoLayoutOptions = {}) {
  const { direction = 'TB', nodesep = 50, ranksep = 50 } = options;
  const { getNodes, getEdges, setNodes, fitView } = useReactFlow();
  const nodesInitialized = useNodesInitialized();
  const layoutApplied = useRef(false);
  const runLayout = useCallback(() => {
    const nodes = getNodes();
    const edges = getEdges();
    const g = new dagre.graphlib.Graph();
    g.setGraph({ rankdir: direction, nodesep, ranksep });
    g.setDefaultEdgeLabel(() => ({}));
    nodes.forEach((node) => {
      g.setNode(node.id, {
        width: node.measured?.width ?? 172,
        height: node.measured?.height ?? 36,
      });
    });
    edges.forEach((edge) => {
      g.setEdge(edge.source, edge.target);
    });
    dagre.layout(g);
    const layouted = nodes.map((node) => {
      const pos = g.node(node.id);
      const width = node.measured?.width ?? 172;
      const height = node.measured?.height ?? 36;
      return {
        ...node,
        position: { x: pos.x - width / 2, y: pos.y - height / 2 },
      };
    });
    setNodes(layouted);
    window.requestAnimationFrame(() => fitView({ duration: 200 }));
  }, [direction, nodesep, ranksep, getNodes, getEdges, setNodes, fitView]);
  // Auto-layout on initialization
  useEffect(() => {
    if (nodesInitialized && !layoutApplied.current) {
      runLayout();
      layoutApplied.current = true;
    }
  }, [nodesInitialized, runLayout]);
  return { runLayout };
}

Usage:

function Flow() {
  const { runLayout } = useAutoLayout({ direction: 'LR', ranksep: 100 });
  return (
    <>
      Re-layout
      
    
  );
}

Edge Options

Control edge routing with weight and minlen:

edges.forEach((edge) => {
  g.setEdge(edge.source, edge.target, {
    weight: edge.data?.priority ?? 1,  // Higher = more direct path
    minlen: edge.data?.minRanks ?? 1,  // Minimum ranks between nodes
  });
});

weight: Higher weight edges are prioritized for shorter, more direct paths.

minlen: Forces minimum rank separation between connected nodes.

// Force 2 ranks between nodes
g.setEdge('a', 'b', { minlen: 2 });

Common Patterns

Handle Position Based on Direction

Adjust handles for horizontal vs vertical layouts:

function CustomNode({ data }: NodeProps) {
  const isHorizontal = data.direction === 'LR' || data.direction === 'RL';
  return (
    

      
      
{data.label}
      
    
  );
}

Animated Layout Transitions

Smooth position changes using CSS transitions:

.react-flow__node {
  transition: transform 300ms ease-out;
}

For programmatic animation, see reference.md.

Layout with Node Groups

Exclude group nodes from dagre layout:

const layoutWithGroups = (nodes: Node[], edges: Edge[]) => {
  // Separate regular nodes from groups
  const regularNodes = nodes.filter((n) => n.type !== 'group');
  const groupNodes = nodes.filter((n) => n.type === 'group');
  // Layout only regular nodes
  const { nodes: layouted } = getLayoutedElements(regularNodes, edges);
  // Combine back
  return { nodes: [...groupNodes, ...layouted], edges };
};

Troubleshooting

Nodes Overlapping

Increase spacing:

g.setGraph({
  rankdir: 'TB',
  nodesep: 100,  // Increase horizontal spacing
  ranksep: 100,  // Increase vertical spacing
});

Layout Not Updating

Ensure new array references:

// Wrong - same reference
setNodes(layoutedNodes);
// Correct - new reference
setNodes([...layoutedNodes]);

Nodes at Wrong Position

Check coordinate conversion:

// Dagre returns center, React Flow needs top-left
position: {
  x: pos.x - width / 2,   // Not just pos.x
  y: pos.y - height / 2,  // Not just pos.y
}

Performance with Large Graphs

• Layout in a Web Worker
• Debounce layout calls
• Use useMemo for layout function
• Only re-layout changed portions

Configuration Reference

See reference.md for complete dagre configuration options.