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 files are always digitally signed. The first time you export, enter a signer name in the dialog to create your signing key.

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.

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 on demand by re-running the stored operation.

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 and Provenance

Exported MDS files are always digitally signed. Signatures use ECDSA P-256 via the Web Crypto API. A signature lets you confirm who ultimately 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.

Saving to the browser (Save to Browser) does not sign anything. Browser storage is a working area that only this browser reads and writes; signatures apply only to exported files that leave the browser.

When opening an MDS file, its signature integrity is verified first. Files without a signature, and 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 file's trust level is determined from its provenance — who created it and who edited and re-exported it:

When you edit someone else's MDS file and re-export it, the exported file carries your signature together with a record of the original creator (the provenance). On the recipient's side, the file's trust level is the lowest trust level among everyone in the provenance. This prevents content from an unknown signer from appearing trusted just because it passed through someone else's signature. If you export without changing anything, the original file is written out unchanged and keeps its original signature.

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, the signature format was updated in July 2026 to include provenance, and MDS files exported before that cannot be opened in the current version. Projects saved to the browser (Save to Browser) before this update also cannot be reopened for the same reason. Re-export any projects you want to keep with Export Project.

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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