Scala Cats

Open-source Scala projects categorized as Cats

Top 23 Scala Cat Projects

  • Scala Exercises

    The easy way to learn Scala.

    Project mention: How to get started? | /r/scala | 2023-06-02
  • Http4s

    A minimal, idiomatic Scala interface for HTTP

    Project mention: How to get started? | /r/scala | 2023-06-02

    http4s is a Typelevel project, and therefore falls into the "program in Scala as if it were Haskell" category. Many people find this off-putting, but honestly, I think with the resources listed above, this is the option at the best intersection of "mature" and "well-documented" available in Scala. The reason it's off-putting to many people is that Haskell-style pure FP isn't mainstream, so it isn't so much a matter of learning a new technology as it is a matter of learning a new paradigm, which necessarily means surfacing and unlearning things you already know, and perhaps confronting the uncomfortable feeling that things you thought were "fundamental," "have to be that way," aren't, and don't. I personally found this process liberating. But not everyone does.

  • InfluxDB

    Collect and Analyze Billions of Data Points in Real Time. Manage all types of time series data in a single, purpose-built database. Run at any scale in any environment in the cloud, on-premises, or at the edge.

  • Monix

    Asynchronous, Reactive Programming for Scala and Scala.js.

    Project mention: Ask HN: What are some of the most elegant codebases in your favorite language? | | 2023-06-17
  • Monocle

    Optics library for Scala

  • skunk

    A data access library for Scala + Postgres.

  • sttp

    The Scala HTTP client you always wanted!

  • scala-pet-store

    An implementation of the java pet store using FP techniques in scala

    Project mention: Scala Resurrection | /r/scala | 2023-01-24

    Hello, you can try to look for pet store implementations on GitHub using Scala, like The "Pet Store" is usually an example repo demonstrating how to build a CRUD service. Since Scala is a language capable of expressing multiple design techniques, multiple ways of solving similar problems exist, which is neither good nor bad, just irritating for a beginner.

  • Onboard AI

    Learn any GitHub repo in 59 seconds. Onboard AI learns any GitHub repo in minutes and lets you chat with it to locate functionality, understand different parts, and generate new code. Use it for free at

  • guardrail

    Principled code generation from OpenAPI specifications

    Project mention: Ask HN: Why is there no specification for Command Line Interfaces? | | 2023-02-27

    What's the use case? I was thinking about this exact issue because my product ships several CLI tools, but I wasn't convinced it would be worth the effort.

    An OpenAPI specification describes an HTTP interface, and I see it as useful because it makes it easier to write code in language-of-choice to generate HTTP requests (by generating client libraries from the OpenAPI spec).

    For a CLI, the interface is the command-line. Usually people type these commands, or they end up in bash scripts, or sometimes they get called from programming language of choice by shelling out to the CLI. So I could see a use case for a CLI spec, which would make it easier to generate client libraries (which would shell out to the CLI)... but it seems a little niche.

    Or maybe, as input to a documentation tool (like Swagger docs). I would imagine if you're using a CLI library like Python's Click, most of that data is already there. Click Parameters documentation:

    Or maybe, you could start from the spec and then generate code which enforces it. So any changes pass through the spec, which would make it easy to write code (server and client-side) / documentation / changelogs. Some projects like this: Guardrail (Scala) , and Connexion (Python) .

    But without this ecosystem of tooling, documenting your CLI in a specification didn't really seem worth the effort. Of course, that's a bootstrapping problem.

  • pfps-shopping-cart

    :shopping_cart: The Shopping Cart application developed in the book "Practical FP in Scala: A hands-on approach"

    Project mention: Scala real world projects | /r/scala | 2023-07-03
  • mouse

    A small companion to cats (by typelevel)

    Project mention: Mouse 0.4.2 - Early release | /r/scala | 2023-11-01

    Not related to another scala lib called mouse?

  • Mockito Scala

    Mockito for Scala language

  • natchez

    functional tracing for cats

  • cats-mtl

    cats transformer type classes.

  • monadless

    Syntactic sugar for monad composition in Scala

    Project mention: "A New Library For Imperative ZIO Programming" by Alexander Ioffe at Functional Scala 2022 | /r/scala | 2023-01-10
  • Pulsar4s

    Idiomatic, typesafe, and reactive Scala client for Apache Pulsar

  • Iteratee

    Iteratees for Cats

  • pfps-examples

    :izakaya_lantern: Standalone examples shown in the book "Practical FP in Scala: A hands-on approach"

  • cats-effect-testing

    Integration between cats-effect and test frameworks

  • meow-mtl

    Next Level MTL for Scala

  • Octopus

    Scala library for boilerplate-free validation (by krzemin)

  • Scala Test-State

    Scala Test-State.

  • mongo4cats

    MongoDB client wrapper for Cats Effect & FS2

  • graalnative4s

    Employ Scala for serverless applications

    Project mention: [Scala] Iniziare con graalvm e http4s | /r/initaliano | 2023-04-21
  • SaaSHub

    SaaSHub - Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020). The latest post mention was on 2023-11-01.

Scala Cats related posts


What are some of the best open-source Cat projects in Scala? This list will help you:

Project Stars
1 Scala Exercises 2,608
2 Http4s 2,470
3 Monix 1,913
4 Monocle 1,616
5 skunk 1,505
6 sttp 1,393
7 scala-pet-store 1,047
8 guardrail 506
9 pfps-shopping-cart 495
10 mouse 344
11 Mockito Scala 332
12 natchez 310
13 cats-mtl 302
14 monadless 271
15 Pulsar4s 218
16 Iteratee 184
17 pfps-examples 182
18 cats-effect-testing 171
19 meow-mtl 163
20 Octopus 150
21 Scala Test-State 138
22 mongo4cats 84
23 graalnative4s 62
SaaSHub - Software Alternatives and Reviews
SaaSHub helps you find the best software and product alternatives