What Is a .dll File? .dll Format, MIME & How to Open

Quick facts

Extension.dll

File typeDynamic Link Library

MIME typeapplication/octet-stream

CategoryData & Text

Charset—

CompressibleYes

Format familyexe

What is .dll

What is a .dll file?

A .dll file is a Dynamic Link Library — Windows shared library of executable code.

In the mime-db registry it maps to application/octet-stream, and it is marked as compressible. When serving .dll over HTTP, set the Content-Type header as shown in Developer info below.

Related entities: it maps to application/octet-stream — and is delivered over HTTP via the Content-Type header.

How to open .dll files

Use Windows or Dependency Walker to open and edit .dll files.
Any text editor (Notepad, VS Code) can inspect the raw content as text.

Developer info

When served over HTTP, responses should set the following header:

Content-Type: application/octet-stream

Common software that reads/writes .dll:

WindowsDependency Walker

Relation chain

.dllextension of

format

exeserved as

mime type

application/octet-streamsent via header

http header

Related extensions

Windows Installer Package

Related MIME types

application/octet-stream

.bin .dms .lrf

application/x-msdownload

.exe .dll .com

Common uses

Configuration files
Data interchange between systems
API request and response payloads
Logs and data exports

How to edit .dll files

Open the file with Windows, make your changes and save.
Most editors preserve the original formatting and encoding — avoid changing the charset.

How to create .dll files

Create a new file and save it with the .dll extension, or export this format from Windows.

Frequently asked questions

What programs can open .dll files?

Common options include Windows, Dependency Walker. You can also open many of these files with built-in viewers or a browser.

How do I create a .dll file?

Create a new file in any text editor or the app that owns the format and save it with the .dll extension.

What is the relationship between .dll and the application/octet-stream MIME type?

application/octet-stream is the media type identifier used for .dll files during network transfer (for example in the HTTP Content-Type header).

Sources & standards

Updated 2026-09-13

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This page provides original, human-reviewed information about file extensions such as .dll, the File Extension Reference and related concepts. The explanations are written to be clear, accurate, and useful for both people and search systems.

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