Signal K is a JSON-based format for storing and sharing marine data from different sources (e.g. nmea 0183, 2000, seatalk, etc)
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Signal K Specification

This repository contains the (working) specification for Signal K, defined in JSON Schema files, tests for the schema files and assorted JavaScript utilities for working with Signal K delta and full JSON data as well as validation utilities.

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Signal K

The Free and Open Source universal marine data exchange

Signal K is about publishing a common modern and open data format for marine use. A format for the modern boat, compatible with NMEA, friendly to WiFi, cellphones, tablets, and the Internet. A format available to everyone, where anyone can contribute.

Find out more at Then join the mailinglist by sending an email to or follow the discussion via the Signal K Google Groups forum.


The master branch contains the latest version of the Schema. When making changes, please clone this repo to your local machine and set up a new branch (git checkout -b branch_name). Send in a pull request for every change, put it up for discussion in the mailing list and then (when a consensus has been reached) merge it into master.

The gh-pages branch contains the currently published version of the schema and specification. Documentation is generated with Gitbook and published at Documentation is published on the web with a single npm command:

$ npm run docs:publish

See below for details.

Gitbook Documentation

The documentation .md sources are at

Requires separate installation of ebook-convert, see

  • npm run docs:serve for local preview
  • npm run docs:all to generate locally
  • npm run docs:publish to publish in gh-pages.

The changelog in the documentation is generated based on Github Pull Requests. For things to show up in the changelog you MUST USE PRs! Rewording is possible by rewriting PR titles.


Validation against Signal K schema can be done

  • with a command line validator accepting JSON from stdin
  • by explicitly calling validate packaged as an npm module
  • by using a Chai assertion, available in the npm module

As you can see in the example below the current implementation assumes that the input is a subtree under vessels.mmsi path.

echo '{"navigation":{"courseOverGroundTru":{"value":70.1,"source":{"label":"","type":"NMEA2000","pgn":"130577","src":"160"},"timestamp":"2014-08-15-10:01:35.236"},"speedOverGround":{"value":0.01,"source":{"label":"","type":"NMEA2000","pgn":"130577","src":"160"},"timestamp":"2014-08-15-10:01:35.236"}}}' | bin/validate.js
Unknown property (not in schema):/vessels/230099999/navigation/courseOverGroundTru
var validate = require('signalk-schema').validate;
var result = validate(msg);
  result.errors.forEach(function(error) {
    console.error(error.message + ':' + error.dataPath);