15Five vs Fastmail

15Five and Fastmail (Open-source software developed at Fastmail.) both appear on the Smoower Developer Ecosystem Index.

Fastmail (rank #430) holds a modest lead over 15Five (rank #693) on the overall Smoower ecosystem score (40 vs 31). The gap of 9 points reflects composite signals across code, docs, community and reach.

On code quality (the state of repositories, tests, releases and polish), 15Five is slightly ahead of Fastmail. On education (docs, guides and learning material for developers), Fastmail is ahead of 15Five. On community (issue response, PR reviews and discussion health), Fastmail is slightly ahead of 15Five. On reach (how visible the ecosystem is beyond its own repos), Fastmail is clearly ahead of 15Five. On momentum (release cadence and how fast the ecosystem moves), Fastmail is ahead of 15Five.

15Five carries 141 GitHub stars across 29 public repos, with 2 repositories active in the last 90 days and 5 external contributors on record. Fastmail shows 6,316 stars across 38 public repos, 12 active in the last 90 days and 2 external contributors. The star gap on its own does not decide the comparison, but Fastmail's footprint is roughly 44.8x larger, which usually shows up in downstream signals like inbound issues and third party integrations.

15Five is the stronger read for anyone weighting code quality. Fastmail looks better where reach is the deciding factor. The table below breaks the scores down pillar by pillar; the linked profiles cover the underlying repos, docs and community signals in full.