dsnts

dsnts is a TypeScript-first toolkit for reading, editing, and generating Specctra DSN (Design) and SES (Session) S-expression documents. Every DSN token is modeled as a class, so you can compose PCB designs, routing data, and component placements entirely in TypeScript and emit Specctra-compatible files with deterministic formatting.

What is Specctra DSN?

Specctra DSN is an industry-standard file format for PCB design and autorouting. DSN files (.dsn) contain board structure, component placement, nets, and design rules. SES files (.ses) contain routing session data with wire paths and via placements. These files are commonly used by:

• FreeRouting - Open-source autorouter
• KiCad - Exports DSN files for external routing
• Altium Designer - Supports DSN import/export
• Commercial autorouters - Specctra, TopoR, etc.

Local Setup

This repository uses Bun for scripts and testing.

• bun install
• bun test — optional, but handy to confirm we still round-trip DSN demo files

Status

⚠️ Work in Progress: This project is currently being converted from kicadts to dsnts. Core DSN parsing and generation functionality is under active development. See TODO.md for the implementation roadmap.

Planned Features

Load Existing DSN Files

Use the specialized parse functions to load and validate DSN or SES files:

import { promises as fs } from "node:fs"
import { parseSpectraDsn, parseSpectraSes } from "dsnts"

// Load and modify a DSN file
const dsn = parseSpectraDsn(await fs.readFile("board.dsn", "utf8"))
dsn.parser = "dsnts"
await fs.writeFile("board.dsn", dsn.getString())

// Load a routing session file
const ses = parseSpectraSes(await fs.readFile("board.ses", "utf8"))
console.log(`Found ${ses.routes?.length || 0} routes`)

Build DSN Files Programmatically

Compose DSN files with structure, placement, library, network, and wiring sections:

import { promises as fs } from "node:fs"
import {
  SpectraDsn,
  Structure,
  Boundary,
  Network,
  Net,
  Library,
  Padstack,
} from "dsnts"

const dsn = new SpectraDsn({
  parser: "dsnts",
  resolution: { unit: "mil", value: 10 },
  structure: new Structure({
    boundary: new Boundary({
      // Board outline
      path: [[0, 0], [100, 0], [100, 80], [0, 80], [0, 0]],
    }),
  }),
  network: new Network({
    nets: [
      new Net({ name: "GND", pins: ["U1-1", "R1-1"] }),
      new Net({ name: "VCC", pins: ["U1-2", "C1-1"] }),
    ],
  }),
})

await fs.writeFile("board.dsn", dsn.getString())

Extract Routing Information

Parse SES files to analyze routing results:

import { promises as fs } from "node:fs"
import { parseSpectraSes } from "dsnts"

const ses = parseSpectraSes(await fs.readFile("board.ses", "utf8"))

// Analyze wire segments
for (const wire of ses.wiring?.wires || []) {
  console.log(`Net: ${wire.net}, Layer: ${wire.layer}`)
  console.log(`Path: ${wire.path.join(" -> ")}`)
}

// Analyze vias
for (const via of ses.wiring?.vias || []) {
  console.log(`Via at ${via.position}, Padstack: ${via.padstack}`)
}

Architecture

dsnts follows the same proven architecture as kicadts:

• S-expression base classes - SxClass handles parsing and serialization
• Token-based class system - Each DSN element (pcb, structure, network, etc.) is a class
• Type-safe constructors - Full TypeScript support with getters/setters
• Round-trip testing - Output matches input formatting exactly
• Flexible syntax - Use objects, arrays, or class instances in constructors

For generic S-expression parsing, use parseSpectraSexpr which returns an array of SxClass instances. Any class exposes getChildren() if you need to walk the tree manually.

Resources

• Specctra DSN Specification (PDF)
• FreeRouting Project - Open-source autorouter
• KiCad DSN Export - How KiCad generates DSN files
• Layout Editor DSN Format - Format overview

Contributing

This project is under active development. Check TODO.md for the current implementation status and roadmap. Contributions are welcome!

License

See LICENSE file for details.