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Version	Package	Description
	ManagedCode.MimeTypes	Core library

MIME (Multipurpose Internet Mail Extensions) values describe the media type of a payload. They appear in HTTP headers, file uploadworkflows, messaging protocols and countless integrations. Unfortunately the canonical values are long strings, which makes codeprone to typos and hard to validate.

ManagedCode.MimeTypes ships a generated helper with more than1,200 extensions sourced from thejshttp/mime-dbproject,Apache's canonicalmime.types list and curated overrides, smart heuristics for multi-part extensions (such as.tar.gz), runtime registration APIs and rich helpers for detecting andcategorising data by content.

• Generated extension → MIME map based on the latest mime-db dataset (plus curated compound extensions such astar.gz,d.ts,ps1, …).
• Rich overrides for lightweight markup and diagram DSLs (AsciiDoc, BibTeX, Org-Mode, PlantUML, Mermaid, Typst, TikZ, …) tailored for AI/document pipelines.
• Reverse lookup API that returns the extensions known for a given MIME value.
• Runtime registration/unregistration so applications can plug in custom corporate formats.
• Content sniffing for common file signatures (PDF, PNG, JPEG, GIF, WebP, MP4, ZIP/OOXML, ODF, APK, etc.) with graceful handling of short or empty streams.
• Extended categorisation enum covering document, audio/video, script, binary, multipart and message families with convenience predicates.
• Safe-by-default mutation model powered by immutable dictionaries, configurable fallback MIME viaMimeHelper.SetDefaultMimeType, and anIMimeHelper abstraction (MimeHelper.Instance) for DI scenarios.
• CLI utility to refreshmimeTypes.json directly frommime-db or a custom source.

usingManagedCode.MimeTypes;// Extension based lookup (handles multi-part extensions automatically)vargzip=MimeHelper.GetMimeType("archive.tar.gz");// application/gzipvartypeScript=MimeHelper.GetMimeType("module.d.ts");// application/typescript// Content-based detectionusingvarstream=File.OpenRead("report.pdf");vardetected=MimeHelper.GetMimeTypeByContent(stream);// application/pdf// Categorisation helpersif(MimeHelper.IsDocument(detected)){// do something useful}// Reverse lookupvarjpegExtensions=MimeHelper.GetExtensions("image/jpeg");// .jpeg, .jpg, .jpe// Runtime registration (and clean-up)MimeHelper.RegisterMimeType("acme","application/x-acme");varcustom=MimeHelper.GetMimeType("invoice.acme");MimeHelper.UnregisterMimeType("acme");// Override the fallback MIME and use the DI-friendly adapterMimeHelper.SetDefaultMimeType(MimeHelper.JSON);IMimeHelperhelper=MimeHelper.Instance;varfallback=helper.GetMimeType("file.unknownext");// application/json (custom fallback)

A small console utility is included to synchronisemimeTypes.json with upstream datasets and our curated overrides. The repository alsoships a scheduled GitHub Actions workflow that runs the sync tool weekly and opens a pull request whenever new MIME definitions are published.

# Update the data file in-placedotnet run --project ManagedCode.MimeTypes.Sync# Provide custom sources or outputDOTNET_CLI_TELEMETRY_OPTOUT=1 dotnet run --project ManagedCode.MimeTypes.Sync -- \    --source https://example.com/primary-mime-db.json \    --add-source https://example.com/additional-mime-map.json \    --output ./artifacts/mimeTypes.json# Start with a clean slate and prefer local overridesdotnet run --project ManagedCode.MimeTypes.Sync -- --reset-sources --prefer-remote

Running the tool re-generates the JSON file, which in turn updates the generated helper during the next build.

dotnet add package ManagedCode.MimeTypes

Issues and PRs are welcome! Rundotnet test before sending a contribution, and feel free to use the sync utility to keep the MIMEcatalogue current.