MDS Files

MDS is the native project file format for MIDAS. The file extension is .mds. An MDS file stores datasets, models, reports, workspace layouts, and other project state in a single file.

Saving and Exporting

There are two ways to save an MDS file. Saving to the browser is for frequent saves while you work; exporting as a file is for sharing with other users and keeping backups.

Save to Browser

File > Save to Browser (Cmd+S / Ctrl+S) saves the project to the browser's storage (OPFS). Saved projects appear in the launcher's Quick Access section and can be reopened with a click.

Because this uses browser storage, saved projects are only accessible from the same browser and profile. They do not appear in other browsers or on other devices. Clearing browser data will delete saved projects. When saving, MIDAS requests persistent storage from the browser. If the request is granted, the data is excluded from automatic eviction under storage pressure. Whether to grant the request is up to the browser, so depending on browser settings and available storage capacity, the browser may still evict this data automatically. Export important projects as files for safekeeping.

Export as File

File > Export Project... (Cmd+Shift+S / Ctrl+Shift+S) downloads an .mds file.

Exported MDS files can be shared with other users or kept as backups. To open a received MDS file, use Open File on the launcher screen. On the recipient's side, the signer appears as Unknown by default. If you exchange public keys in advance, the file will be recognized as Trusted. See Managing Signing Keys for details.

About Auto-Save

MIDAS does not perform real-time auto-save. To preserve your work, save explicitly using either method above. When you close a project or open another project within MIDAS, a confirmation dialog appears if there are unsaved changes. Closing the browser tab shows no confirmation dialog and discards any unsaved changes.

If you set up a backup folder, an MDS file is also written to that folder every time you save. See Storage Management > Backup Folder for setup instructions.

Data Excluded from Saving

Primary Dataset row data (the original datasets imported from CSV or similar sources) is included in the MDS file. Derived Datasets (datasets produced by queries or transformations) are saved as definitions only; their row data is not saved by default. After opening a project, data is recomputed from the parent dataset in the MDS file on demand.

This keeps MDS files small. For Derived Datasets with expensive queries, enable Materialized View to persist the computed data. See Datasets > Materialized View for details.

Digital Signatures

When you save or export an MDS file, it is automatically signed with your signing key. The signing key is generated automatically on first save, so no prior setup is required. Signatures use ECDSA P-256 via the Web Crypto API. A signature lets you confirm who created the file (which key signed it) and also detects tampering that occurs after signing. Signatures do not encrypt the file contents; anyone who obtains the MDS file can read its contents.

When opening an MDS file, its signature integrity is verified first. Files that fail verification due to tampering or corruption during transfer cannot be opened. See Managing Signing Keys for how to handle verification failures.

If verification passes, the signer's trust level determines how the file is handled:

By default, an MDS file from an unknown signer opens without a confirmation dialog. This is safe because paths from unknown-signed files to external servers are blocked at load time. See Privacy and Security for details. The signature badge at the top-right of the menu bar shows the unknown trust level, so you can check the fingerprint and decide whether to trust the signer before running further analysis. To require explicit confirmation for every unknown signature, open Help > Settings... and enable Require confirmation for unknown signers on the Security tab.

For managing signing keys, exporting public keys, and registering others' keys, see Managing Signing Keys.

Data Locality

All data processing in MIDAS happens entirely within the browser. Project data is never sent to any external server. Data is stored in the browser's local storage areas (OPFS and IndexedDB), and exported MDS files are simply downloaded to the user's device. For details on how each storage is used, see Storage Management.

The signing key is also stored in the browser and never sent to any external server. Clearing browser data destroys the signing key, and MDS files you previously signed will be treated as Unknown. For key backup, see Managing Signing Keys.

Version Compatibility

MDS files carry a MIDAS version number. When you open an older MDS file in a newer version of MIDAS, migrations are automatically applied. However, MDS files saved before version 2025.12.19 have no digital signature and cannot be opened in the current version.

When you open an MDS file saved by a newer version of MIDAS in an older version, a warning is shown. The file still opens, but some features may not work correctly. Because MIDAS is a web app, this situation mainly occurs when the browser has cached an older version of MIDAS. Reloading the page updates it to the latest version.

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