Build notes from a solo office suite.
Technical posts from the work in Casual Sheets, Casual Editor, and Casual Slides. Yjs CRDT bridges, Hocuspocus production patterns, .xlsx + .pptx round-trip lessons, capacity modelling, and the production-readiness work behind each release. No marketing — just what shipped and why.
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Measuring the WebSocket broadcast ceiling of a single Node process
We modelled the broadcast ceiling of a Hocuspocus + Yjs CRDT backend at ~500 active docs per Node process. Then we measured it. The model was 10× too conservative — the real bottleneck is somewhere else entirely.
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Load testing without k6: a 190-line Node-only HTTP harness
Before you reach for k6 or artillery, try a Node script. Built-in fetch + perf_hooks gives you p50/p95/p99 in 190 lines, zero new dependencies, and runs anywhere Node runs. Real numbers from the Casual Sheets v0.2.0 production-readiness pass.
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Yjs replay retry: classifying transient vs permanent failures in a CRDT bridge
When a Yjs CRDT bridge fails to apply a remote mutation, the difference between "network blip during chunk-load" and "malformed mutation params" matters a lot. We added a 50-line classifier and a 4-second retry budget. Silent divergences became user-visible recoverable state.
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Rate limiting and room caps for a Hocuspocus + Fastify backend
A production-readiness pass on a Yjs realtime backend: per-route token-bucket rate limiting via @fastify/rate-limit, a MAX_ROOMS cap with two-pass LRU eviction, and a 503 capacity_full envelope. Three small pieces that turn "denial-of-service-by-loop" into "tight-but-bounded write surface."
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When deepRewriteUnitId isn't deep enough: a Yjs CRDT bridge bug
A cross-peer drawing sync bug in a Yjs + Hocuspocus collaborative spreadsheet. The fix wasn't where we expected. A story about positional arrays, json1 op paths, and why "the skipped test header explains the bug" is a comforting lie.
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