Space Script allows you to extend SilverBullet with JavaScript from within your space using space-script Blocks. It’s script... in (your) space. Get it?

warning Security
Space script allows for arbitrary JavaScript to be run in the client and server, there are security risks involved if malicious users get write access to your space (folder) or if you copy & paste random scripts from the Internet without understanding what they do.
If this makes you very queazy, you can disable Space Script by setting the SB_SPACE_SCRIPT environment variable to off

Creating scripts

Space scripts are defined by simply using space-script fenced code blocks in your space. This can happen on any Pages you like, but for organizational reasons it’s recommended you put them on Meta Pages.

You will get JavaScript Syntax Highlighting for these blocks.

Here is a trivial example:

silverbullet.registerFunction({name: "helloYeller"}, (name) => {
  return `Hello ${name}!`.toUpperCase();

You can now invoke this function in a template or query:


Upon client and server boot, all indexed scripts will be loaded and activated. To reload scripts on-demand, use the command (bound to Ctrl-Alt-r for convenience).

If you use things like console.log in your script, you will see this output either in your server’s logs or browser’s JavaScript console (depending on where the script will be invoked).

Runtime Environment & API

Space script is loaded directly in the browser environment on the client, and the Deno environment on the server.

Depending on where code is run (client or server), a slightly different JavaScript API will be available. However, code should ideally primarily rely on the following explicitly exposed APIs:

  • silverbullet.registerFunction(def, callback): registers a custom function (see #Custom functions).
  • silverbullet.registerCommand(def, callback): registers a custom command (see #Custom commands).
  • silverbullet.registerEventListener: registers an event listener (see #Custom event listeners).
  • silverbullet.registerAttributeExtractor(def, callback): registers a custom attribute extractor.
  • syscall(name, args...): invoke a syscall (see #Syscalls).

Many standard JavaScript APIs are available, such as:

  • fetch (making fetch calls directly from the browser on the client, and via Deno’s fetch implementation on the server)
  • Temporal (implemented via a polyfill)

Custom functions

SilverBullet offers a set of Functions you can use in its Template Language. You can extend this set of functions using space script using the silverbullet.registerFunction API.

Since template rendering happens on the server (except in Client Modes#Synced mode), this logic is typically executed on the server.

The silverbullet.registerFunction API takes two arguments:

  • def: with currently just one option:
    • name: the name of the function to register
  • callback: the callback function to invoke (can be async or not)


Even though a Functions#readPage(name) function already exist, you could implement it in space script as follows (let’s name it myReadPage) using the syscall API (detailed further in #Syscalls):

silverbullet.registerFunction({name: "myReadPage"}, async (name) => {
  const pageContent = await syscall("space.readPage", name);
  return pageContent;

Note: this could be written more succinctly, but this demonstrates how to use async and await in space script as well.

This function can be invoked as follows:

{{myReadPage("internal/test page")}}

Custom commands

You can also define custom commands using space script. Commands are always executed on the client.

Here is an example of defining a custom command using space script:

silverbullet.registerCommand({name: "My First Command"}, async () => {
  await syscall("editor.flashNotification", "Hello there!");

You can run it via the command palette, or by pushing this command link:

The silverbullet.registerCommand API takes two arguments:

  • def:
    • name: Name of the command
    • key (optional): Keyboard shortcut for the command (Windows/Linux)
    • mac (optional): Mac keyboard shortcut for the command
    • hide (optional): Do not show this command in the command palette
    • requireMode (optional): Only make this command available in ro or rw mode.
  • callback: the callback function to invoke (can be async or not)

Custom event listeners

Various interesting events are triggered on SilverBullet’s central event bus. Space script can listen to these events and do something with them.

The silverbullet.registerEventListener API takes two arguments:

  • def, currently just one option:
    • name: Name of the event. This name can contain * as a wildcard.
  • callback: the callback function to invoke (can be async or not). This callback is passed an object with two keys:
    • name: the name of the event triggered (useful if you use a wildcard event listener)
    • data: the event data

To discover what events exist, you can do something like the following to listen to all events and log them to the JavaScript console. Note that different events are triggered on the client and server, so watch both logs:

silverbullet.registerEventListener({name: "*"}, (event) => {
  // To avoid excessive logging this line comment it out, uncomment it in your code code to see the event stream
  // console.log("Received event in space script:", event);


Let’s say you want to automatically add a completion date to a task whenever you complete it, the Tasks plug emits a task:stateChange event you can listen to:

silverbullet.registerEventListener({name: "task:stateChange"}, async (event) => {
  const {from, to, newState} =;
  if(newState !== " ") {
    // Now dispatch an editor change to add the completion date at the end of the task
    await syscall("editor.dispatch", {
      changes: {
        from: to, // insert at the end of the task
        insert: " ✅ " + Temporal.Now.plainDateISO().toString(),

Custom attribute extractors

SilverBullet indexes various types of content as Objects. There are various ways to define Attributes for these objects, such as the syntax. However, using space script you can write your own code to extract attribute values not natively supported using the registerAttributeExtractor API.

The silverbullet.registerAttributeExtractor API takes two arguments:

  • def with currently just one option:
    • tags: Array of tags this extractor should be applied to, could be a built-in tag such as item, page, paragraph, header, or task, but also any custom tags you define.
  • callback: the callback function to invoke (can be async or not). This callback is passed the following arguments:
    • text: the text of the object to extract attributes for
    • return value: an object of attribute mappings, possibly overriding built-in ones.

Note that indexing happens on every page save. You have to run to have the new attribute extractor apply across changes in your entire space.


Let’s say you want to use the syntax ✅ 2024-02-27 in a task to signify when that task was completed and strip it from the task name. Here’s an example:

  • I’ve done this ✅ 2024-02-27

The following attribute extractor will accomplish this:

silverbullet.registerAttributeExtractor({tags: ["task"]}, (text) => {
  // Find the completion date using a regular expression
  const completionRegex = /✅\s*(\w{4}-\w{2}-\w{2})/;
  const match = completionRegex.exec(text);
  if (match) {
    // Let's patch the task name by stripping the completion date
    // First strip the checkbox bit from the text
    let taskName = text.replace(/\[[^\]]+\]\s*/, "");
    // Then remove the completion date and clean it up
    taskName = taskName.replace(completionRegex, "").trim();
    // That should be all
    return {
      name: taskName,
      completed: match[1]

{{{task where page = select name, completed}}}


The primary way to interact with the SilverBullet environment is using “syscalls”. Syscalls expose SilverBullet functionality largely available both on the client and server in a safe way.

In your space script, a syscall is invoked via syscall(name, arg1, arg2) and usually returns a Promise with the result.

Here are all available syscalls:

{{#each @module in {syscall select replace(name, /\.\w+$/, "") as name}}}
## {{}}
{{#each {syscall where = replace(name, /\.\w+$/, "")}}}
* `{{name}}`