.SD file extension
To open .SD files on Windows, install a tool that supports MDL SD/SDF, such as Open Babel (the command-line tool is often named "obabel").
To open a .sd file, use a chemistry/cheminformatics program that supports MDL SD/SDF (for example, Open Babel). If you don’t have a compatible app, the file is plain text, so you can also inspect it with a text editor, but that won’t render the chemical structure visually.
Last updated: June 10, 2026
Open on your device
Choose your operating system for a dedicated step-by-step opening guide.
How to open .SD files
Use these platform-specific instructions to open .SD files safely.
Windows
- Install a tool that supports MDL SD/SDF, such as Open Babel (the command-line tool is often named "obabel").
- Open/convert the file: use Open Babel to read .sd and (optionally) convert it to another format (e.g., SDF, MOL, SMILES) if needed.
- If you only need to inspect content, open the .sd file in a plain text editor to view records and property tags.
Mac
- Install a tool that supports MDL SD/SDF, such as Open Babel (command-line "obabel").
- Use Open Babel to open/convert the .sd file into another format your workflow expects (e.g., .sdf, .mol, .smi).
- For quick troubleshooting, open it in a text editor to confirm it looks like an SDfile (structure block plus tagged data fields).
Linux
- Install a tool that supports MDL SD/SDF, such as Open Babel (command-line "obabel").
- Open or convert the file with Open Babel; Linux desktops may also identify it via the shared MIME database depending on your environment.
- If you just need to validate the contents, view it as text to check record delimiters and property fields.
iOS
- iOS typically won’t provide a native preview for SDfile chemistry data; transfer the .sd file to a desktop cheminformatics tool (for example, Open Babel) to view/convert it.
Android
- Android typically won’t provide a native viewer for SDfile chemistry data; transfer the .sd file to a desktop cheminformatics tool (for example, Open Babel) to view/convert it.
Security notes
- An SDfile is data (text) and normally not executable, but it can still be risky if opened in vulnerable chemistry parsers; only open SDfiles from trusted sources in up-to-date tools.
- Be cautious with very large SDfiles (many records or huge property blocks): they can cause high memory/CPU usage or application crashes when imported.
- If you receive an .sd file that doesn’t look like chemistry data when opened as text, treat it as suspicious or misnamed and verify the source before proceeding.
Can't open this file?
These are the most common causes and fixes when .SD files fail to open.
Common reasons
- The .SD file opens as unreadable text or in the wrong app
- Import fails or only some molecules load
- File type identification (MIME) is inconsistent across systems
Fix steps
- Open it with a cheminformatics tool that supports MDL SD/SDF (for example, Open Babel).
- If your workflow expects .sdf, convert the file to .sdf using a proper converter rather than renaming the extension.
OS-specific troubleshooting
What is a .SD file?
.sd (SDfile) is a Structure-Data Format (SDF) chemical table file used to represent one or more molecules along with key–value property data. It is a text format originally associated with MDL formats (MOL/SD/SDF) and is commonly used for exchanging compound libraries and annotations. Many tools treat .sd and .sdf as the same underlying format.
Background
An SDfile (often seen as .sdf, but sometimes .sd) is a standard way to bundle molecular structures with metadata such as identifiers, measured properties, and other annotations. Each record typically contains a structure block (MDL MOL-style) followed by tagged data fields, making it convenient for storing datasets of many compounds in a single file.
This format is widely used in chemistry and bioinformatics workflows, for example when moving compound collections between databases, modeling tools, and screening pipelines. Because it is plain text, it is also easy to generate and parse, and can be inspected with any text editor for troubleshooting.
In practice, users open .sd files with cheminformatics tools that can interpret MDL MOL/SD/SDF. Open Babel specifically documents read/write support for MDL MOL/SD/SDF and recognizes extensions including .sd and .sdf.
Common MIME types: chemical/x-mdl-sdfile
Other meanings of .SD
The extension .SD is used by several programs. Besides the file type described on this page, it can also stand for:
- ESPS Sampled Data
- Sound Designer Audio File
Further reading
Authoritative resources for more details on the .SD format.
Common .SD issues
The .SD file opens as unreadable text or in the wrong app
An SDfile is plain text, so the OS may default to a text editor instead of a chemistry tool, and a text editor won’t visualize structures.
- Open it with a cheminformatics tool that supports MDL SD/SDF (for example, Open Babel).
- If your workflow expects .sdf, convert the file to .sdf using a proper converter rather than renaming the extension.
Import fails or only some molecules load
SDfiles can contain multiple records; importers may stop on a malformed record, unexpected tags, or nonstandard variations.
- Try reading/converting the file with Open Babel, which supports MDL MOL/SD/SDF and can often handle variations.
- Inspect the file as text around the point of failure to look for truncated records or missing separators, then re-download or re-export the dataset.
File type identification (MIME) is inconsistent across systems
MIME type mapping can vary by platform and desktop environment; Linux often relies on the freedesktop shared MIME database and local overrides.
- On Linux, update or check your shared-mime-info database and file associations if your desktop misidentifies .sd files.
- When sharing files, consider using the more explicit .sdf extension if your collaborators’ tools expect it.
FAQ
Is .sd the same as .sdf?
Often, yes. In chemistry, “SD file” refers to the SDF/SDfile Structure-Data Format, and many tools treat .sd and .sdf as the same format.
How can I tell if my .sd file is an SDfile (SDF) in practice?
Open it in a text editor: SDfiles are plain text and typically contain a MOL-style structure block followed by tagged property fields (common in SDF/SDfile datasets).
Can I convert an .sd file by renaming it to .sdf (or another extension)?
No. Renaming only changes the filename; use a converter such as Open Babel to convert between SD/SDF and other chemical formats.
What MIME type is commonly associated with SDfile/SDF?
A commonly used MIME type for SDF/SDfile is chemical/x-mdl-sdfile, though MIME handling can vary by platform and may not be formally consistent everywhere.
Similar file extensions
Compare related formats in the same category to find the right tool faster.