This is a Dart implementation of the Ebisu quiz scheduling algorithm, originally developed in Python by Ahmed Fasih.

In a nutshell, Ebisu works by modelling the probability that a fact will be remembered correctly at any arbitrary moment since the last time the fact was last quizzed. For more information, refer to the excellent literate document describing the original implementation.

This ebisu_dart package is unrelated to the similarly named ebisu package.


import 'package:ebisu_dart/ebisu.dart';

// Assume an inital halflife of 10 units (interpreted as minutes here).
const initialHalflife = 10.0;
var model = EbisuModel(initialHalflife);

// Predict recall after 30 minutes have elapsed.
final predictedRecall = model.predictRecall(30.0);

// Update model after a correct answer.
model = model.updateRecall(1, 1, 30.0);

// Calculate new halflife.

Porting notes

This Dart implementation is a fairly literal port of the Java implementation, but converted into idiomatic Dart: object oriented, no separation of interface/class, named and optional method arguments, and so on. To keep the excellent documentation of the original version relevant, method names have not been changed, even though this results in slightly worse naming.

Documentation comments have been ported and updated from the Java version, but for an in-depth explanation of the algorithm, refer to the original.


The major version number follows that of the Python implementation while also obeying semantic versioning; thus, API-breaking changes can only happen if a new major version of the Python implementation is released.


All unit tests of the original Python implementation have been ported. To run them:

pub test

To run the linter (configured with the rules from the pedantic package):

dartanalyzer .

To publish a new version:

  • Update the version number in pubspec.yaml.
  • Update CHANGELOG.md.
  • Commit the changes with a message of the form vX.Y.Z: Brief summary.
  • Add a tag of the form vX.Y.Z.
  • Run git push && git push --tags to push the code and tag to GitHub.
  • Run pub publish --dry-run to check if everything is okay.
  • Run pub publish to publish.


Public domain (see the LICENSE file).


Implementation of the Ebisu quiz scheduling algorithm: https://fasiha.github.io/ebisu/