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.
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. Depending on browser settings and available storage capacity, the browser may 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, drag and drop it onto the launcher screen or use Open File.
About Auto-Save
MIDAS does not perform real-time auto-save. To preserve your work, save explicitly using either method above. Closing the browser tab discards any unsaved changes.
Data Excluded from Saving
Primary Dataset row data is included in the MDS file. Derived Datasets are saved as definitions (queries and transformation operations) 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. Signatures identify the signer and detect tampering that occurs after signing.
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.
If verification passes, the signer's trust level determines how the file is handled:
| Trust Level | Description |
|---|---|
| Official | Signed by the MIDAS operator's key |
| Trusted | Signed by your own key or a registered public key |
| Unknown | Signed by an unregistered signer |
By default, an MDS file from an unknown signer opens without a confirmation dialog. 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. Strict mode can be enabled under Settings > Security to require explicit confirmation for every unknown signature.
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 OPFS and IndexedDB, and exported MDS files are simply downloaded to the user's device. Digital signatures use the Web Crypto API (ECDSA P-256); signing keys are never sent to any external server. For this reason, clearing browser data also destroys the signing key, and MDS files you previously signed will be treated as Unknown. For key backup, see Managing Signing Keys.
For details on how each storage is used, see Storage Management.
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.
When you open an MDS file saved by a newer version of MIDAS in an older version, a warning is shown. Some features may not work correctly.