Rust Hover Preview

A Windows 11 tray app inspired by QTTabBar. Hover a file in File Explorer — or move with the arrow keys — and a preview appears beside it. It works with mouse and keyboard, and you configure it from the tray icon or a simple config.ini.

Showcase.webm

Highlights

• Mouse-hover and keyboard-navigation previews in Explorer.
• Previews appear beside the cursor or focused item and are kept on screen.
• Supports previews for images, design documents, camera raw, vector drawings, fonts, videos, PDFs, ebooks, comics, text/code, archives, Office documents, and more.
• A file’s preview depends on what’s really inside it—not its name—so renamed files still show correctly, unreadable content gets no preview, and ambiguous types are resolved by extension or content.
• Scaling from 25% to 400%, or fit-to-screen. Separate scaling for images and videos, and for vector drawings, PDFs, documents, fonts, and design documents.
• Tray menu and hand-editable config.ini.
• DPI aware, single-instance, sleep/resume resilient, and light on idle CPU.

Supported Formats

You can add or remove formats in config.ini. Unsupported formats show no preview, except text, which the app will try to force-read.

Almost everything is previewed by Windows 11 and this app alone — a codec Windows ships, WebView2, the drawing layer that plays metafiles, the Windows PDF engine, or a reader written into the app. Six things are not, and they are the app’s largest optional dependencies:

Runs on Windows 11 alone

Kind	Extensions
Pictures	jpg jpeg jfif jpe png apng gif bmp ico tif tiff tga hdr exr ff qoi pnm pam pbm pgm ppm dds webp
Pictures through a Windows codec extension	heic heif avif avci jxl
Videos Windows 11 plays itself	mp4 m4v mov qt avi wmv asf dvr-ms mkv webm ts m2ts mts m2t mpg mpeg mpe m2v m1v vob 3gp 3g2 3gpp
Sounds Windows 11 plays itself	mp3 wav wave m4a m4b aac wma aif aifc aiff amr awb flac dsf
Drawings	svg svgz (WebView2) · wmf emf (the drawing layer) · eps epsi epsf epi ept ept2 ept3 (the preview the file carries)
Design documents	psd psb ai kra ora procreate sketch fig xd
Fonts	ttf otf ttc woff woff2 (WebView2)
Ebook	pdf pdfa epdf (the Windows PDF engine) · cbz cbr cbc
Text and code	adb adoc ads asciidoc asm asp aspx astro awk bash bat bib bzl c cc cfg cg cjs clj cljc cljs cmake cmd comp conf cpp cs csh cshtml css csv csx cts cxx d dart diff diz edn ejs el elm env erb erl ex exs f f03 f77 f90 f95 fish for frag fs fsi fsx ftn fx geom glsl go gql gradle graphql groovy h haml hbs hcl hh hlsl hpp hrl hs htm html hxx inc ini ipynb java jl js json json5 jsonc jsonl jsp jsx ksh kt kts latex less lhs liquid lisp ll lock log lsp lua m mak man markdown md mdown metal mjs mk mkd ml mli mm mts mustache nasm nfo nim ninja nix njk org pas patch php phtml pl plist pm properties proto ps1 psd1 psm1 py pyi pyw r rake rb rkt rmd rs rst rtf s sass scala scm scss sh slim sol sql srt ss styl sv svelte svh swift tcl tex text tf tfvars toml ts tsv tsx twig txt v vbs vert vhd vhdl vtt vue wat wgsl xhtml xml xsd xsl xslt yaml yml zig zshExtensionless / Specific Files:authors .babelrc brewfile caddyfile changelog changes .clang-format .clang-tidy cmakelists.txt code_of_conduct containerfile contributing contributors copying copyright dockerfile .dockerignore .editorconfig .env .env.example .env.local .eslintignore .eslintrc gemfile .gitattributes .gitconfig .gitignore .gitkeep .gitmodules gnumakefile .golangci.yml history .htaccess install jenkinsfile justfile licence license .mailmap makefile makefile.am makefile.in notice .npmignore .prettierignore .prettierrc procfile rakefile readme .rustfmt.toml security .stylelintrc unlicense vagrantfile
Archives	7z apk jar rar tar tar.gz tgz xpi zip zipx

Notes on the table

Animated GIF, APNG and WebP play. hdr and exr are tone-mapped for preview. dds previews BC1–BC7, both BC6H variants and uncompressed textures — including packed HDR and depth — at the first face and the nearest-size mip.

Needs FFmpeg

Videos the table does not already cover need FFmpeg, and these are all of them: 264 265 266 apv av1 avc avs avs2 avs3 bik bk2 c93 cavs cdg cdxl cin cpk dav dif divx drc dv evc f4v flm flv gxf h261 h263 h264 h265 h266 h26l hevc ifv imx ismv ivf ivr kux m2p mj2 mjpeg mjpg mk3d moflex mpv mve mvi mxf mxg nsv nut obu ogm ogv pmp psp rcv rm rmvb roq rsd smk str swf thp tod tp tr ty ty+ usm vc1 vc2 viv vro vvc vw wtv xl xmv y4m yop.

The containers and codecs the table above lists are the ones Windows plays on its own, and they play better with FFmpeg installed — more codecs inside the same container, and seeking rather than a still frame. The tray's Codecs menu shows what this machine can play.

Sounds Windows does not decode need FFmpeg as well, and these are all of them: ac3 ape au caf dff dts dtshd eac3 mka mp2 mpa mpc oga ogg ofr ofs opus ra shn snd spx tak tta voc wv

Needs Microsoft Office, or LibreOffice

Office documents — doc docm docx dot dotm dotx xls xlsb xlsm xlsx xlt xltm xltx ppt pptm pptx pps ppsm ppsx pot potm potx — are drawn in the background by an installed Office so previews appear quickly after the first hover. Excel needs a print queue to export a page — Microsoft Print to PDF is enough, and the Print Spooler service must be enabled; without one, Excel falls back to the sheet’s top-left corner. Where no Office is installed, an installed LibreOffice draws them instead. To have LibreOffice draw them all — with Microsoft Office installed as well — use Engine → Select Engine → Office and pick LibreOffice.

Needs LibreOffice

The documents this app has no reader of its own for, drawn by an installed LibreOffice and sharp at any size, all of them: 123 602 abw cdr cgm cmx cwk dbf dif dxf fodg fodp fodt gnm gnumeric hwp key lwp mcw met mw numbers odb odc odf odg odm odp ods odt oth otg otm otp ots ott pages pcd pct pcx pdb pm6 pmd psw pub ras sda sdc sdd sdw slk stc std sti stw svm sxd sxg sxi sxm sxw vdx vsd vsdm vsdx vstx wb2 wk1 wk3 wk4 wks wpg wq1 wq2 wpd wps wri xlw zabw zmf.

Needs ImageMagick

ImageMagick previews otherwise-unopenable files—especially camera raws—at display size, rotated, decoded from memory. Raws/own-coder: 3fr arw cr2 cr3 crw cur dcm dcr dcx dng dpx erf fff fit fits fts iiq j2c j2k jng jp2 jpc jpm jpt k25 kdc mdc mef miff mng mos mrw nef nrw orf pef pfm raf raw rmf rw2 rwl sgi sr2 srf srw vicar wbmp x3f xbm xcf xpm. Alternates/other engine names: pict (pct), sun (ras), pcds (pcd), dxt1/dxt5 (dds), icb vda vst, picon, group4; Raw sample dumps: rgb rgba gray cmyk ycbcr mono group4 and the rest; dimensions inferred by trying aspect ratios against file length—first exact divisor wins, else none; transpose ambiguity can make portrait landscape.

Needs PeaZip

The archives this app has no reader of its own for, listed by an installed PeaZip and shown as the same page of contents a .zip is shown as, all of them: 001 apfs ar arc arj bcm br bz2 bzip2 cab chm cpio cramfs deb dmg esd gz gzip hfs hfsx hxs iso lha lit lpaq8 lzh lzma msi msp pkg ppkg qcow qcow2 rpm squashfs swm taz tbz tbz2 tpz txz tzst udf udeb vdi vhd vhdx vmdk wim xar xip xz z zpaq zst. A .tar.gz and a .tgz are the archive list’s above and stay this app’s own.

Needs Calibre

The ebooks this app has no reader of its own for, converted by an installed Calibre and drawn as a page of the PDF it wrote — the same kind, scale and backdrop a PDF this app reads itself gets, all of them: azw azw3 azw4 djvu epub fb2 htmlz lit lrf mobi pml prc snb tcr.

A book with DRM — an .azw, .azw3 or .azw4 bought from Amazon — cannot be converted by anything here and shows nothing. See TODO.md for the formats the engine reads that are not in the list, and why.

Themes

Text, code, and archive listings use Atom One Light by default, One Dark Pro, or any .tmTheme file placed in:

%APPDATA%\rust-hover-preview\theme

Installation

Each release provides two options:

• rust-hover-preview_<version>_x64-setup.exe — NSIS installer. Installs to %LOCALAPPDATA%\rust-hover-preview with an optional startup entry.
• rust-hover-preview.exe — portable standalone binary. Run it from any folder.

Steps:

1. Open Releases.
2. Download your preferred asset.
3. Run the installer, or place the portable binary wherever you like.
4. Launch Rust Hover Preview.

No Rust toolchain is needed. If upgrading from an earlier version, the installer cleans up the old %LOCALAPPDATA%\Rust Hover Preview folder automatically.

Optional: Enable Video Preview with FFmpeg

Videos preview without FFmpeg through the media engine Windows ships with. FFmpeg adds far more formats and codecs. Install it if you want formats Windows does not decode. ffplay and ffprobe need to be in your PATH.

Option A: winget

winget install --id Gyan.FFmpeg -e

Option B: manual

1. Download a Windows build from https://ffmpeg.org/download.html
2. Extract it, for example to C:\ffmpeg
3. Add C:\ffmpeg\bin to your user PATH

Verify either way:

ffplay -version
ffprobe -version

Optional: Enable More Video Codecs (Windows Codecs) — They are not needed while FFmpeg is installed.

The media engine decodes H.264, MPEG-4, and WMV out of the box. Each codec below is a separate free extension from the Microsoft Store:

Codec	Needs
HEVC (H.265)	HEVC Video Extensions
VP9	VP9 Video Extensions
AV1	AV1 Video Extension
MPEG-1 and MPEG-2	MPEG-2 Video Extension
Theora, Vorbis and Opus in an Ogg file	Web Media Extensions

All are free. Windows 11 usually has HEVC, VP9, and AV1 already. Installing one takes effect the next time the tray’s Codecs menu is opened — no restart, nothing to configure.

Optional: Enable HEIC, AVIF, JPEG XL and WebP Preview (Windows Codecs)

heic, heif, avif, jxl, and still webp are decoded by a codec Windows provides rather than one shipped with the app. Each needs its extension installed once from the Microsoft Store:

Format	Needs
heic, heif	HEIF Image Extension + HEVC Video Extensions
avif	HEIF Image Extension + AV1 Video Extension
jxl	JPEG XL Image Extension, or the JXL support optional feature on Windows 11 24H2
webp	WebP Image Extension — optional: the app decodes WebP without it

All are free. Windows 11 often has HEIF, AV1, and WebP already. Where one is missing, hovering such a file shows no preview rather than an error, and a multi-image file — a HEIC burst, an animated AVIF, an animated JPEG XL — shows its first frame. A .webp is the exception: it needs none of them, because the app carries its own libwebp decoder, so WebP previews even on Windows 10.

Optional: Enable CorelDRAW and Other Documents (LibreOffice)

cdr and everything else in the [libre] list is drawn by LibreOffice, which this app drives where it finds it — nothing is bundled with the app and there is nothing to configure. Install it once:

winget install -e --id TheDocumentFoundation.LibreOffice

Or download the official installer from https://www.libreoffice.org/download/ and run the suggested file (LibreOffice_*_Win_x86-64.msi; LibreOffice ships an .msi, not an .exe).

Optional: Enable Camera Raw and More Pictures (ImageMagick)

nef and everything else in the [magick] list is developed by ImageMagick, which this app runs where it finds it — nothing is bundled with the app and there is nothing to configure. Install it once:

winget install -e --id ImageMagick.ImageMagick

Or download the official installer from https://imagemagick.org/download/ and run the suggested file (ImageMagick-*-Q16-HDRI-x64-dll.exe).

Optional: Enable Niche Archives (PeaZip)

cab and everything else in the [peazip] list is listed by PeaZip, which this app runs where it finds it — nothing is bundled with the app and there is nothing to configure. Install it once:

winget install -e --id Giorgiotani.Peazip

Or download the official installer from https://peazip.github.io/peazip-64bit.html and run the suggested file (peazip-*.WIN64.exe).

Optional: Enable Ebooks (Calibre)

mobi and everything else in the [calibre] list is converted by Calibre, which this app runs where it finds it — nothing is bundled with the app and there is nothing to configure. Install it once:

winget install -e --id calibre.calibre

Or download the official installer from https://calibre-ebook.com/download_windows and run the suggested file (calibre-*-64bit.msi).

Warning

If winget reports an error, the package sources are usually why: run winget source reset --force.

If that is refused as well, open Terminal as administrator (right-click the Start button → Terminal (Admin)) and run the same command from there.

Usage

1. Start the app — a tray icon appears.
2. Hover media files in Explorer to preview them.
3. Or navigate with the keyboard — arrow keys, Tab, or a file's name typed to jump to it — to preview the focused item.
4. Right-click the tray icon to configure behavior.

Here is a concise, plain-language version:

System Tray Menu

A setting marked (Default) is what an untouched setting would be. The check or radio mark shows what is set now.

• Enable Preview — Turn previews on or off.
• Preview Types — Choose which file kinds can preview: Images, Videos, Audio, Text, Ebook, Archives, Document, Vector, Fonts, Design. One switch covers both the original file and the engine-drawn preview. Examples: camera raw uses Images; LibreOffice document uses Document; PeaZip archive uses Archives; Calibre book uses Ebook — also the app-drawn PDF and comic pages.
• Text Preview
  • Full Mode — Adds scrolling, selection, and copy. Off by default.
  • Theme — Atom One Light, One Dark Pro, or any .tmTheme in the theme folder.
  • Font Size — 400% at the top down to 70% at the bottom.
  • Markdown — Rendered or Source.
• Timing
  • Prioritize Keyboard — On by default. The file under a pointer that has not been moved does not preview of its own while the keyboard is driving Explorer, so pressing a key onto a file with no preview of its own behaves like pressing one onto a file that has a preview. The pointer takes the screen back when it is moved, when the wheel is turned, or when a folder change hands it over. Off, the pointer's own hover always wins.
  • Trigger Key (Alt) — The key is named in the item.
    • Enable Trigger Key — Whether the key is watched.
    • Hold to Disable Preview / Hold to Enable Preview — What holding the key does.
  • Delay — How long the pointer rests before a preview opens: 0 ms at the top down to 1000 ms at the bottom. Default 0 ms.
  • Rehover Delay — Wait before the same file can preview again. Default 200 ms.
  • Settling Delay — How still the pointer must be before previewing what it is on. Default 0 ms means a new file can preview while the hand is still moving. Keyboard previews ignore this.
• Placement
  • Position — Follow Cursor or Best Position. Default Best Position.
  • Avoid — Avoid Nothing, Avoid Filename (default), Avoid Filename Column, or Avoid Details. Keeps a preview off the item it is about. Keyboard previews have no cursor, so Avoid Nothing acts like Avoid Filename.
• Scaling
  • Image Scaling — Fit to Screen or 25%–400% of the image’s own size.
  • Video Scaling — Same shares for a video. Default 100%.
  • Animated Scaling — Same shares for an animated GIF, WebP, or PNG. A still GIF or PNG uses Image Scaling. Default 100%.
  • Vector Scaling — Fit to Screen (default), or 75%, 50%, 25%, 10% of the display.
  • Ebook Scaling — Fit to Screen (default), or the same display shares for a PDF page, a comic’s first page, and a Calibre-converted book.
  • Document Scaling — Same display shares for a document drawn as a page, whether by its own Office app or by LibreOffice. A workbook’s fallback bitmap is never enlarged.
  • Font Scaling — Same shares for a font specimen. Default 50%.
  • Design Scaling — Same display shares for design documents: Photoshop, Illustrator, Krita, OpenRaster, Procreate. Default Fit to Screen.
• Background
  • Image Background — Transparent, Black, White, or Checkerboard. Default Checkerboard.
  • Vector Background — Same backdrops for an SVG document or metafile. Default Checkerboard.
  • Font Background — Same backdrops for a font specimen. Default White.
  • DDS Background — Black or White for .dds textures. Default White. The two see-through backdrops are not offered.
  • Design Background — Same as picture backdrops for a design document. Default Checkerboard.
• Volume — Video and Audio, each offering 0%, 1%, 5%, 10%, 20%, 35%, 50%, 65%, 80% and 100%. A video's soundtrack starts at 0% — silent, so a hover never makes a sound the pointer did not ask for — and a sound file at 10%: a video is looked at and a song is listened to, so the two are settings of their own. A sound at 0% still shows its card, silently.
  • Audio Seek — Where in a file a hovered sound starts playing: Remember (default) picks it up where the last hover left it, From the Start always begins at the beginning, From the Middle drops it half way in, and Random anywhere at all. The remembered positions are kept in a small file under %TEMP%\rust-hover-preview\audio, so they survive a restart; nothing is remembered while another mode is chosen. Whatever a sound is started at, it goes back to the beginning of the file when it reaches the end of it and loops from there for as long as the hover lasts. A video is always played from its beginning.
• Performance
  • Cache — What a preview may cost between hovers: 2 GB down to 0 MB. Image (RAM) = decoded frames kept in memory. Document (Disk) = engine-drawn pages kept as temp files. Image (Disk) = the pictures ImageMagick developed, kept as temp files.
  • Decode Budget — 16 GB down to 512 MB; default 1 GB. A file past it gets no preview.
  • Tick — How often the app checks Explorer while a folder window is focused: 15 ms (default), 31, 47, 63, or 78 ms. Lower answers a move sooner; higher is lighter on CPU and Explorer.
• Engine
  • AFK Timer — How long Explorer may be unreachable before a non-Persistent engine is let go: 1 hour, 30 minutes, 10 minutes, 5 minutes, 1 minute (default), 30 seconds, 15 seconds. Counts time when no Explorer window is reachable on any monitor. A second Explorer window keeps engines warm. Each … TTL submenu has a Persistent toggle at the top.
  • Select Engine → Office — Which engine draws Office documents: Microsoft Office (default) uses the format’s own app and falls back to LibreOffice; LibreOffice draws every Office document. LibreOffice is greyed out if not installed.
  • Microsoft Office TTL — With Persistent on: how long a family’s Office app stays warm: Indefinitely, 1 hour, 30 minutes, 10 minutes (default), 5 minutes, 1 minute, 0 seconds. Off: kept while Explorer is reachable, then let go by AFK Timer.
  • LibreOffice TTL — Same for the engine that draws CorelDRAW and nearby formats. A kept engine converts the next document faster: 1.2 s cold vs 0.2 s, but uses a few hundred MB. 0 seconds means one engine per document. Both TTLs apply to Persistent engines; non-persistent ones use AFK Timer. Greyed out if LibreOffice is not installed.
  • WebView2 TTL — With Persistent on: how long the SVG browser stays warm. Off: let go by AFK Timer. Greyed out if WebView2 is missing.
  • No ImageMagick TTL, PeaZip TTL, or Calibre TTL: those tools run once and exit, so idle time cannot bound them. A second hover is a cache hit.
• Codecs — What this machine has: Videos, Audio, Images, Engines. A missing one carries a cross, and where the README names a page for it, picking the row offers to open that page — nothing is installed or downloaded by the app itself.
• Run at Startup — Add or remove the Windows startup entry.
• Config.ini — Open the configuration file; named for the running version.
• Exit — Close the app.

Configuration

Settings are stored at:

%APPDATA%\rust-hover-preview\config.ini

The file is watched, and changes apply without a restart.

Example, trimmed:

[settings]
; General
preview_enabled=true
run_at_startup=true

; Preview Types
archive_preview_enabled=true
design_preview_enabled=true
document_preview_enabled=true
ebook_preview_enabled=true
font_preview_enabled=true
image_preview_enabled=true
text_preview_enabled=true
vector_preview_enabled=true
video_preview_enabled=true

; Text Preview
markdown_mode=rendered
text_font_scale=125
text_preview_full_mode=false
theme=light

; Timing
hover_delay_ms=0
prioritize_keyboard=true
same_file_rehover_delay_ms=200
settling_delay_ms=0
trigger_key=alt
trigger_key_enabled=true
trigger_key_mode=disable

; Placement
avoid_mode=filename
follow_cursor=false

; Scaling
animated_scale=100
design_scale=fit
document_scale=fit
ebook_scale=fit
font_scale=50
preview_scale=100
vector_scale=fit
video_scale=100

; Background
dds_background=white
design_background=checkerboard
font_background=white
image_background=checkerboard
vector_background=checkerboard

; Volume
audio_seek=remember
audio_volume=10
video_volume=0

; Performance
decode_budget_gb=1
document_cache_mb=256
image_cache_mb=64
image_disk_cache_mb=512
tick_ms=15

; Engine
afk_timer_seconds=60
libreoffice_idle=600
libreoffice_persistent=false
office_engine=microsoft_office
office_engine_idle=600
office_engine_persistent=false
webview_idle=600
webview_persistent=false

; Advanced
hdr_exposure=0
hdr_tone_map=reinhard
spinner_delay_ms=250

Here’s what this .INI does:

Look and text

• theme: light, dark, or custom:<name>.
• markdown_mode: show Markdown as rendered or source.
• text_preview_full_mode: true adds scrolling, selection, and copy.
• text_font_scale: 1–1000%, default 125; archive lists follow it too.

What can preview

• *_preview_enabled: turn each preview type on or off. File lists stay normal.
• extensions / names: which files get text previews. Extensions have no dots. names matches files with no extension.
• image_extensions, video_extensions, archive_extensions, office_extensions, font_extensions, design_extensions, vector_extensions: per-type preview filters. No dots. An entry with a dot, like tar.gz, matches the end of the file name.
• audio_extensions: which files are previewed as sounds. One list rather than two, because which engine plays a file is the machine's answer and not a setting: Windows' own decoders are asked first and an installed FFmpeg second.
• ebook_extensions, libre_extensions, magick_extensions, peazip_extensions, calibre_extensions: pages this app draws itself — PDFs, comic covers, LibreOffice documents, ImageMagick pictures, PeaZip archives, and Calibre books.

Memory and cache

• image_cache_mb: memory for decoded image frames. Default 64, max 2048; 0 holds nothing.
• document_cache_mb: disk cache for rendered document pages. Default 256, max 2048; 0 keeps nothing between hovers but still draws the current one. Pages live under %TEMP%\rust-hover-preview\document; the least recently read page is removed first.
• image_disk_cache_mb: disk cache for the pictures ImageMagick developed. Default 512, max 2048; 0 keeps nothing between hovers but still develops the current one. Pictures live under %TEMP%\rust-hover-preview\image; the least recently read one is removed first, and they survive a restart.
• decode_budget_gb: most memory one hover may use. Default 1, range 0.25–64. A file over the limit shows no preview.

HDR

• hdr_tone_map: how HDR/EXR light becomes screen values: reinhard default, aces, srgb, or off. PNG/JPEG are not affected.
• hdr_exposure: stops shifted before that curve. Default 0, range -10 to 10.

Waiting and engines

• spinner_delay_ms: wait before showing the loading spinner. Default 250; 0 shows it immediately. One delay covers all preview types.
• office_engine: microsoft_office default, falls back to LibreOffice when needed; or libreoffice, which always uses LibreOffice. If LibreOffice is missing, it falls back and the tray row is greyed out.
• libreoffice_idle: seconds LibreOffice is kept after its last page, or indefinitely. Default 600; 0 launches it per document.
• office_engine_idle: same idea for the Office engine. Default 600; 0 lets it go after drawing a page.
• afk_timer_seconds: seconds with no Explorer window before a non-persistent engine is released. Default 60, max one day. 0 releases immediately.
• office_engine_persistent, libreoffice_persistent, webview_persistent: true keeps that engine always, bounded only by its …_idle time. false default keeps it while Explorer is reachable, bounded by afk_timer_seconds.

Trigger and position

• trigger_key / trigger_key_mode / trigger_key_enabled: the key (alt, ctrl, shift, win), what it does (disable or enable), and whether it is watched. Default true.
• follow_cursor: true = Follow Cursor; false = Best Position.
• avoid_mode: filename default, filename_column, details, or off — what the preview avoids.

Scaling

• preview_scale: percentage or fit, based on the picture’s own size.
• video_scale: same for video. Default 100.
• animated_scale: same for animated GIF, WebP, or PNG. Default 100. Still GIF/PNG follow preview_scale.
• vector_scale: percentage or fit, based on the screen. Default fit; 100 or more reads as fit. Covers all Vector drawings. Old svg_scale is ignored and removed.
• ebook_scale: PDF page scale against the screen. Default fit; 100 or more reads as fit.
• document_scale: document page scale against the screen. Default fit. A workbook’s fallback bitmap keeps its own size and is never enlarged.
• font_scale: font preview scale against the screen. Default 50; fit means all of it; 100 or more reads as fit.
• design_scale: design document scale against the screen. Default fit.

Fonts

• ttc_face: which face of a .ttc is drawn. 1 is first, max 10. The heading shows which face came out.

Backgrounds

• image_background: checkerboard default, black, white, or transparent. Also used for PDF pages, painted text frames, and document pages. Old transparent_background is ignored and removed.
• font_background: white default, black, checkerboard, or transparent.
• dds_background: white default or black, and only those two. Any other value reads as white.
• vector_background: checkerboard default, white, black, or transparent. Used for SVG pages and metafiles. Old svg_background is ignored and removed.
• design_background: checkerboard default, white, black, or transparent.

Old or removed names

• magick_preview_enabled and peazip_preview_enabled: not read. ImageMagick pictures use image_preview_enabled; PeaZip archives use archive_preview_enabled.
• libre_preview_enabled and libre_scale: gone. Use document_preview_enabled and document_scale.
• office_cache_mb and libre_cache_mb: gone. Use document_cache_mb. If both old ones exist, the larger is read once, then both are removed.
• No magick_idle, peazip_idle, or calibre_idle. ImageMagick, PeaZip, and Calibre are converters, not engines kept open. A second hover usually costs only a cache hit.

Extension list behavior

• A deleted extensions= line or whole section comes back with built-in entries.
• An extensions= line left empty stays empty.

Build from Source

Requirements: Windows 11, Rust 1.98.1+, Visual Studio Build Tools (MSVC / C++), and the Windows SDK.

cargo build            # debug
cargo build --release  # release

The release binary is written to target/release/rust-hover-preview.exe. A release build ends a running copy first, since Windows will not let the linker replace an open binary. Debug builds are left alone.

Architecture

See ARCHITECTURE.md for the full system overview. In short: Windows accessibility APIs and Shell COM identify the hovered or focused Explorer item. GDI paints the preview into a topmost layered window. Text and code are highlighted with TextMate-style themes, Markdown is rendered, archive contents are listed from the archives’ own tables of contents — or from the listing an installed PeaZip produces for the formats no reader here has — Office documents are drawn from a page Office renders in the background, WebView2 draws SVG documents and font specimens, camera raw and the pictures beside it are developed by ImageMagick, and video is played by FFmpeg where installed and by Windows’ own media engine where it is not.

TODO

See TODO.md for planned work, known bugs, and other issues.

Privacy

Rust Hover Preview is local-first, previews work without an internet connection, and the only network request is an update check, which runs only when you open the tray menu and at most once an hour. There is no telemetry, analytics, ads, accounts, or crash reporting. It reads only the item you hover or focus in Explorer, locally and only for enabled preview types. Cloud-only placeholders are skipped on purpose; password-protected files are never bypassed. Settings and themes live under %APPDATA%\rust-hover-preview; optional previews use locally installed FFmpeg, LibreOffice, or ImageMagick when available, plus Microsoft Office, Windows' own media engine, and the Windows PDF engine. Caches are bounded by config.ini: decoded images stay in memory, while the page an engine drew for a document — an Office export, a converted PDF — is kept as a file under the temp folder, where Windows is free to clear it. See PRIVACY.md for full details.

License

MIT. See LICENSE.

The app is built out of other people’s code as much as its own — the Windows bindings, the image decoders, the syntax highlighter, the archive readers, the browser bindings — and each of those carries its own licence, with the notices MIT and BSD ask to be reproduced. THIRD-PARTY.md lists every dependency grouped by licence, with the copyright holders beside it, and the full texts are in LICENSES/. Both are generated from the dependency tree rather than kept by hand; generate-attribution.ps1 refreshes them.