Browser CoreNot another PDF editor.A browser-native runtime engine.
Local-first. Realtime. Deterministic. The document engine that renders, edits and replays entirely in the browser.
Contract Agreement
Pointer (1024, 768)
Local-first by design
No white-mask hacks
Every operation tracked
WebGL → WebGPU roadmap
45/45 tests passing
The browser runtime, end to end
Every edit flows through a deterministic, local-first pipeline.
Zero roundtrips for preview. Full fidelity. Realtime.
01PDF bytesActive source bytes enter local runtime.Source⌄
Active PDF bytes enter the browser runtime as the source of truth.
What this solvesFeeds PDFium, workers and textless rendering from the same byte source.
Restored documents can rehydrate bytes from backend export into local cache.
✓Active PDF bytes helper returns memory-hit / indexeddb-hit / indexeddb-miss
✓Restored documents can hydrate bytes from backend export into browser cache
✓Worker requests receive a transferable ArrayBuffer copy
✓Debug exposes pdfBytesAvailable and pdfByteLength
02IndexedDB cacheLocal stores keep sessions warm.Persistence⌄
Document bytes, session metadata, rasters, textless tiles and operation logs persist locally.
What this solvesRefresh can restore page raster and operation replay without waiting for backend preview.
Cache misses are visible instead of silently degrading the runtime.
✓Document/session metadata opens during browser core bootstrap
✓pageRasterBitmaps persists PNG Blob page rasters for refresh restore
✓textlessTileBitmaps persists dirty tile PNG Blobs
✓documentOperationLogs stores replayable local edits
03PDFium WASMWASM rasterizes pages in browser.Renderer⌄
PDFium renders page rasters in-browser through the provider pipeline.
What this solvesMoves page raster production into the browser runtime.
Keeps Python core and preview-image as explicit fallbacks.
✓WASM asset served locally from /vendor/pdfium/pdfium.wasm
✓Renderer URL can be npm:pdfium using @embedpdf/pdfium
✓Lifecycle states: disabled, missing-url, loading, loaded, load-failed
✓PdfPageRasterRenderer.renderPageRaster(input) is the binding boundary
04Text indexWorker maps chars and objects.Index⌄
Worker opens PDFium page/textPage and builds char and text object indexes.
What this solvesTextless tiles can match dirty rects to actual PDF text objects.
Warm page/text cache avoids rescanning the same page on later tiles.
✓Progress waits for PDFium runtime, document, page and text page readiness
✓Char index and text object index are counted in toolbar status
✓Worker keeps PDFium document/page/textPage session warm per PDF fingerprint and page
✓Provider debug reports matched chars and matched text objects
05Render graphDirty nodes compile into buffers.Structure⌄
Operations compile into dirty nodes, dirty regions and command buffers.
What this solvesReact sends commands; Browser Core decides what invalidates and redraws.
Debug snapshots expose dirty/final buffers instead of hiding render state.
✓Render graph forms dirty nodes and dirty regions from setTextStyle/moveLayer ops
✓Dirty command buffer is separate from graph command buffer
✓Final composite command buffer is the production draw path
✓Frame Debug exports status, operation log, render graph and command buffers
06Textless tileClean tiles remove source text.Raster⌄
Worker renders dirty tiles without original PDF text using the provider fallback policy.
What this solvesRemoves original PDF text without white-mask overlays.
Fallback reasons and quality metadata stay visible in debug.
✓Worker request type is render:textless-tile
✓Fallback policy: pdfium-wasm -> pdf-layer -> synthetic-background
✓PDFium toggles matched text objects inactive before rasterizing the tile
✓Quality metadata includes provider, method, attempts, timings and matched char count
07Final compositeLayers merge into final preview.Composite⌄
Production preview composites base raster tiles and replacement text into the final frame.
What this solvesSuccessful preview path no longer depends on drawRect masking.
Operation replay rebuilds the same final composite after refresh.
✓Final composite uses drawBaseRasterTile and drawTextRun
✓drawSelection stays out of production composite
✓drawRect remains graph/dirty debug only, not final output
✓Replay rebuilds render graph, pending textless tile requests and final composite
PDF bytes
SourceActive PDF bytes enter the browser runtime as the source of truth.
What this solvesFeeds PDFium, workers and textless rendering from the same byte source.
Restored documents can rehydrate bytes from backend export into local cache.
Technical details
type ActivePdfBytesResult = {
status: 'memory-hit' | 'indexeddb-hit' | 'indexeddb-miss';
pdfBytes?: ArrayBuffer;
byteLength?: number;
}IndexedDB session cache
PersistenceDocument bytes, session metadata, rasters, textless tiles and operation logs persist locally.
What this solvesRefresh can restore page raster and operation replay without waiting for backend preview.
Cache misses are visible instead of silently degrading the runtime.
Technical details
IndexedDB stores: documentSessions pageRasterBitmaps textlessTileBitmaps documentOperationLogs
PDFium WASM raster
RendererPDFium renders page rasters in-browser through the provider pipeline.
What this solvesMoves page raster production into the browser runtime.
Keeps Python core and preview-image as explicit fallbacks.
Technical details
resolvePageRaster(input) -> memory -> indexeddb -> pdfium-wasm -> python-core -> worker -> preview-image
Text page index
IndexWorker opens PDFium page/textPage and builds char and text object indexes.
What this solvesTextless tiles can match dirty rects to actual PDF text objects.
Warm page/text cache avoids rescanning the same page on later tiles.
Technical details
PDFium text layer readiness: runtime loaded document opened page loaded text page loaded char index built text object index counted
Render graph
StructureOperations compile into dirty nodes, dirty regions and command buffers.
What this solvesReact sends commands; Browser Core decides what invalidates and redraws.
Debug snapshots expose dirty/final buffers instead of hiding render state.
Technical details
Render Graph -> Render Nodes -> Render Commands -> Command Buffer -> Canvas/WebGL/WebGPU Surface
Textless tile worker
RasterWorker renders dirty tiles without original PDF text using the provider fallback policy.
What this solvesRemoves original PDF text without white-mask overlays.
Fallback reasons and quality metadata stay visible in debug.
Technical details
type BrowserCoreWorkerRequest =
| { type: 'render:textless-tile';
tileId: string;
rect: RenderRect;
}Final composite
CompositeProduction preview composites base raster tiles and replacement text into the final frame.
What this solvesSuccessful preview path no longer depends on drawRect masking.
Operation replay rebuilds the same final composite after refresh.
Technical details
finalCompositeBuffer = [ drawBaseRasterTile(tileBitmap), drawTextRun(replacementSpan) ];
No backend roundtrips for preview or edits.
Same inputs, same outputs. Every time.
60 FPS target with predictable frame times.
Source-level text suppression for perfect selection.
Every edit is logged and replayable.
Your documents never leave your device.
No backend roundtrip for every edit
The local runtime previews text style and move operations before authoritative save/export.
No white-mask replacement story
The core is moving toward real textless tile composition with PDFium WASM and provider fallbacks.
State is replayable
Operation replay, compaction and committed state make the preview feel recoverable instead of temporary.
Deep tech. Built different.
Purpose-built runtime technology, not legacy editor layers. Engineered for performance, determinism and full control in the browser.
Render graph
Core runtimeLayer and node based rendering with deterministic dirty invalidations.
Textless tiles
RenderingPDFium-powered source suppression instead of error-prone overlay hacks.
Operation replay
ReliabilityLocal edits can survive refresh and compact into committed state.
Interaction runtime
PerformanceLayer focus, spatial index, ownership and worker resolve path.
GPU-first target
AccelerationCanvas now, WebGL compositor next, WebGPU-ready structure.
SDK potential
PlatformA possible runtime layer for document SaaS, legal tools and e-signature products.
Local-first by design
Preview locally. Commit authoritatively.
Operation replay
Honest roadmap
Make the unfinished parts visible. That is stronger than pretending this is a finished generic SaaS.
Show operation log, compacted ops, committed ops and replay source in a dedicated view.
Measure warm-cache PDFium textless rendering and optimize matching / encode path.
Move final composite toward GPU layer pipeline and texture cache.
Better text rendering path for speed, clarity and consistent previews.
Compare optimistic preview against final authoritative PDF export.
Built for teams building the future of documents
SaaS platforms
Embed low-latency PDF interaction into web products.
Legal tech
Contract editing, review and annotation workflows.
eSignature
Faster flows with realtime visual feedback.
Automation
Document transformations with deterministic operations.
Developers
Potential SDK/runtime layer for custom tools.
Show the engine before it is “finished”.
Position it honestly as an early technology preview and collect serious interest from people who understand document runtimes.