# tumblr/colossus

I/O and Microservice library for Scala

Repository: https://github.com/tumblr/colossus
Canonical: https://ross.abutalabs.com/products/colossus
Language: Scala
License: Apache-2.0
License Family: permissive
Topics: scala, microservice-framework
Last push: 2021-08-14T08:40:07+00:00

## Health v2 (maintenance only)
Score: 23/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 0, release rhythm 8, longevity 100
- inputs: {"age_days": 4313, "days_push": 1845, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1129, forks 95 (observed 2026-08-28T04:03:42.119606+00:00)

## What it is
Colossus is a lightweight I/O framework for building high-performance Scala microservices, including an HTTP server/client and a standalone metrics library. It was developed by Tumblr and participates in the TechEmpower web framework benchmarks.

## Use cases
- build a scala microservice
- high-performance http server in scala
- non-blocking i/o service framework for jvm
- collect and report service metrics
- write scala http clients

## When to choose
- you are building Scala services on the JVM and want a lightweight, non-blocking I/O framework
- you need a simple HTTP server/client with built-in metrics support

## When to avoid
- your team primarily uses Java, Kotlin, or another non-Scala JVM language
- you need a framework with a large ecosystem and frequent updates, as the latest release dates to 2021

## Facets
- artifact type: framework
- maturity: maintenance
- function: http-server, http-client, microservices, monitoring, serialization, testing
- domain: backend, microservices, web-development, developer-tools
- platform: jvm
- tags: scala, nio, high-performance, service-framework, metrics, linux, macos

## Member repositories
- tumblr/colossus (main) score 23

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:03:42.119606+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T06:38:27.885420+00:00, confidence not recorded.
  - readme: https://github.com/tumblr/colossus (fetched 2026-08-28T04:03:42.119606+00:00, sha 060c3e372ef0)
- Data as of 2026-08-30T08:39:29.467469+00:00.