NKESSLING@TERMINALRTM 18:16:33 · UTC 16:16
FERN ~/work/fern EXPERIMENTAL
FERN★ 612▼ 0.14 commits/day, 40 wkZIG · 2025–26
A small config language with types
Compiles to JSON, checks types, and fails the build before a bad config reaches production.
COMMIT RATE · 40 WEEKS · FERN
0.4 mscompile a 2k-line config
31type errors caught in the first month
48 KBWASM build
README.md · CASE STUDY
Compiles to JSON, checks types, and fails the build before a bad config reaches production.
Compiles to JSON, checks types, and fails the build before a bad config reaches production.
Two outages in one quarter came from a config value with the wrong type. fern is a tiny language with records, unions and exhaustive match that compiles to plain JSON.
Where it runs
A 48 KB WebAssembly build runs in CI and in the editor, so the error shows up where the typo was made.
SCRN WORK · SCREENER6 OF 8 SHOWN
More projects.
Every project opens the same way: problem, fix, numbers.
ROLEKEY RESULT
TIDEA write-ahead log that survives the power cordtidewaterAuthor · maintainerRust2024–264,8121.92 GB/s append, one coreKILNA build cache that made CI six times fasterkilnAuthorGo2023–262,2076.1x faster CI, medianLOOMA Postgres job queue that stays fair under loadloom-queueAuthor · 3 contributorsTypeScript2024–251,39012k/s jobs on one nodeWRENRelease notes that write themselves from commitswrenAuthorTypeScript2025–261,04511 min saved per releasePRSMRead traces in the terminal and diff two runsprism-traceAuthorRust2025961O(n log n) trace diff, was O(n²)FERNA small config language with typesfernAuthorZig2025–266120.4 ms compile a 2k-line configNOTE WRITING · RESEARCH NOTES8 NOTES
Notes from the work.
Short write-ups of things that broke and how they got fixed. Plain language, real numbers.