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This is a linkpost for https://usedagger.com/

18 March 2024: I've decided to split the two input formats after all, so Dagger has been replaced by Carlo (spreadsheet) and Probly (programming language). Old URLs  redirect to the appropriate place.

Dagger (usedagger.com) is a new tool for calculations with uncertainty. It uses Monte Carlo simulation.

There are two ways to specify your simulation model:

ℹ️  Each of the two links above has 4 interactive examples. You might want to start there.



In this 15-second video, we take a complex existing spreadsheet (100+ rows) from GiveWell and turn it into a Monte Carlo simulation

The sheet already gives us "optimistic/pessimistic" values, so it's as simple as adding one column to specify the distribution as (e.g.) uniform

(Longer version of this video)


Dependency graph

Intuitive and mathematically rigorous sensitivity analysis

Our sensitivity analysis uses Sobol’ global sensitivity indices. The approach and the intuition behind it are explained in more detail here.

ℹ️  You need to enable the sensitivity analysis under "Advanced options"

Summary table

This table exposes the structure of your model by showing the dependency graph as a tree. Similar to Workflowy, you can zoom to any variable, or expand/collapse


Probly feels very like Python, except that any number can also be a probability distribution:


Here's a fuller example of the syntax and resulting output. It's part of a GiveWell CEA of iron and folic acid supplementation.

Distribution support

Probly supports 9 probability distributions. Each can be constructed in multiple ways.

For example, you can construct a normal distribution in 5 ways:

This clickable table shows you everything that's supported, and includes example code:

ℹ️  Shortcut: probly.dev redirects to usedagger.com/probly


There are at the moment numerous limitations. A small selection of them:

  • Probly:
    • Doesn’t support the Sobol' sensitivity analysis
    • Doesn't show the dependency graph
  • Spreadsheet
    • There is no UI in Dagger to edit the model. All changes must go via the spreadsheet.
    • The spreadsheet must specify probability distributions in a specific format.
  • All models are public




Sorted by Click to highlight new comments since:

I've fully rewritten the spreadsheet tool, available at carlo.app:

The major improvements are:

  • More flexible input format
  • Interactive — histograms update as you edit the spreadsheet (this also means you can collaborate in real time)
  • Overhauled UI with dozens of new features

Other improvements include:

  • Simulations run many times faster — this is especially noticeable for the sensitivity analysis
  • You no longer need to manually type in the result cell coordinate
  • Multiple output variables are now supported
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