squiggle/packages/website/docs/Overview.mdx

---
sidebar_position: 1
title: Overview
---

import { SquiggleEditor } from "../src/components/SquiggleEditor";

Squiggle is a minimalist programming language for probabilistic estimation. It's meant for intuitively-driven quantitative estimation instead of data analysis or data-driven statistical techniques.

The basics of Squiggle are fairly straightforward. This can be enough for many models. The more advanced functionality can take some time to learn.

## Simple example

Say you're trying to estimate the number of piano tuners in New York City. You can build a simple model of this, like so.  
(Tip: This is interactive! Feel free to modify the code directly.)

<SquiggleEditor
  defaultCode={`
// Piano tuners in NYC over the next 5 years
populationOfNewYork2022 = 8.1M to 8.4M // This means that you're 90% confident the value is between 8.1 and 8.4 Million.\n
proportionOfPopulationWithPianos = {
    percentage = (.2 to 1)
    percentage * 0.01
} // We assume there are almost no people with multiple pianos\n
pianoTunersPerPiano = {
    pianosPerPianoTuner = 2k to 50k // This is artificially narrow, to help graphics later
    1 / pianosPerPianoTuner
} \n
totalTunersIn2022 = populationOfNewYork2022 * proportionOfPopulationWithPianos * pianoTunersPerPiano
totalTunersIn2022
`}
/>

---

Now let's take this a bit further. Let's imagine that you think that NYC will grow over time, and you'd like to estimate the number of piano tuners for every point in time for the next few years.

<SquiggleEditor
  defaultCode={`// Piano tuners in NYC over the next 5 years
populationOfNewYork2022 = 8.1M to 8.4M\n
proportionOfPopulationWithPianos = {
    percentage = (.2 to 1)
    percentage * 0.01
} // We assume there are almost no people with multiple pianos\n
pianoTunersPerPiano = {
    pianosPerPianoTuner = 2k to 50k // This is artificially narrow, to help graphics later
    1 / pianosPerPianoTuner
} \n
//Time in years after 2022
populationAtTime(t) = {
    averageYearlyPercentageChange = -0.01 to 0.05 // We're expecting NYC to continuously grow with an mean of roughly between -1% and +4% per year
    populationOfNewYork2022 * ((averageYearlyPercentageChange + 1) ^ t)
}\n
median(v) = quantile(v, .5)
totalTunersAtTime(t) = populationAtTime(t) * proportionOfPopulationWithPianos * pianoTunersPerPiano\n
{
    populationAtTime: populationAtTime,
    totalTunersAtTimeMedian: {|t| median(totalTunersAtTime(t))}
}`}
/>

If you haven't noticed yet, you can hover over the `populationAtTime` graph to see the distribution of population at different points in time.

## Using Squiggle

You can currently interact with Squiggle in a few ways:

**[Playground](/playground)**  
The [Squiggle Playground](/playground) is a nice tool for working with small models and making prototypes. You can make simple sharable links, but you can't save models that change over time.

**[Visual Studio Code Extension](https://marketplace.visualstudio.com/items?itemName=QURI.vscode-squiggle)**  
There's a simple [VS Code extension](https://marketplace.visualstudio.com/items?itemName=QURI.vscode-squiggle) for running and visualizing Squiggle code. We find that VS Code is a useful editor for managing larger Squiggle setups.

**[Typescript Library](https://www.npmjs.com/package/@quri/squiggle-lang)**  
Squiggle is built using [Rescript](https://rescript-lang.org/), and is accessible via a simple Typescript library. You can use this library to either run Squiggle code in full, or to call select specific functions within Squiggle (though this latter functionality is very minimal).

**[React Components Library](https://www.npmjs.com/package/@quri/squiggle-components)**  
All of the components used in the playground and documentation are available in a separate component NPM repo. You can see the full Storybook of components [here](https://squiggle-components.netlify.app).

**[Observable](https://observablehq.com/@hazelfire/squiggle)**  
You can use Squiggle Components in Observable notebooks. Sam Nolan put together an exportable [Observable Notebook](https://observablehq.com/@hazelfire/squiggle) of the key components that you can directly important and use in your Observable notebooks.

## Squiggle Vs. Other Tools

### What Squiggle Is

- A simple programming language for doing math with probability distributions.
- An embeddable language that can be used in Javascript applications.
- A tool to encode functions as forecasts that can be embedded in other applications.

### What Squiggle Is Not

- A complete replacement for enterprise Risk Analysis tools. (See [Crystal Ball](https://www.oracle.com/applications/crystalball/), [@Risk](https://www.palisade.com/risk/), [Lumina Analytica](https://lumina.com/))
- A [probabilistic programming language](https://en.wikipedia.org/wiki/Probabilistic_programming). Squiggle does not support Bayesian inference.
- A tool for substantial data analysis. (See programming languages like [Python](https://www.python.org/) or [Julia](https://julialang.org/))
- A programming language for anything other than estimation.
- A visually-driven tool. (See [Guesstimate](https://www.getguesstimate.com/) and [Causal](https://causal.app/))

### Strengths

- Simple and readable syntax, especially for dealing with probabilistic math.
- Fast for relatively small models. Strong for rapid prototyping.
- Optimized for using some numeric and symbolic approaches, not just Monte Carlo.
- Embeddable in Javascript.
- Free and open-source.

### Weaknesses

- Limited scientific capabilities.
- Much slower than serious probabilistic programming languages on sizeable models.
- Can't do Bayesian backwards inference.
- Essentially no support for libraries or modules (yet).
- Still very new, so a tiny ecosystem.
- Still very new, so there are likely math bugs.
- Generally not as easy to use as Guesstimate or Causal, especially for non programmers.

## Organization

Squiggle is one of the main projects of [The Quantified Uncertainty Research Institute](https://quantifieduncertainty.org/). QURI is a nonprofit funded primarily by [Effective Altruist](https://www.effectivealtruism.org/) donors.