Local Mask | Auto-mask & restore sensitive data

1Enter / paste text

Enter text that contains sensitive information and press “Mask.” Detected items are replaced with tokens like [NAME_1].

High-accuracy name/org analysis (kuromoji)

Uses a Japanese morphological dictionary to also catch names without honorifics and proper nouns not in the built-in list. Turning it on downloads the analysis dictionary (~17 MB) from this site (same origin) on first use only. Your input text is never sent.

2Masked result

Mapping table (token ↔ original)

Stored in your browser (IndexedDB) · 0 items

Token	Original (sensitive)	Category

Automatically discarded when you close the tab (configurable in settings).

3Restore (demask) — turn the AI's reply back

Paste an AI reply that still contains the tokens, and it is instantly restored to the original terms using the mapping table.

Process whole folders / files locally

Load all text files in a folder at once and mask them in parallel inside your browser. The originals are left untouched and saved as name_masked.ext. Everything stays on your device — nothing is uploaded.

Drag & drop files

or click to select (.txt / .log / .csv / .json / .md / .html, etc.)

“Open folder” writes directly into the same folder on Chrome/Edge (File System Access API). On unsupported browsers or with “Select files,” it falls back to download saving.

Detected terms are appended to the same mapping table as “Round-trip clipboard,” so they restore across both.

Even huge files (e.g. a 100 MB log) are processed in line-by-line chunks without freezing the screen. Only text file extensions are processed.

Toggle detection categories

Switch detection targets to fit your use case. Settings are saved on this device (localStorage).

Custom term list

Register your own must-mask terms such as project names or internal codes.
Type term=alias to set a custom token (e.g. Orion=PROJECT_X).

Privacy settings

Auto-discard mapping when the tab closes

Reliably erases the in-browser mapping data when the session ends.

Your input text, files, and mapping table are never sent to any external server. All processing stays within this browser.

01What this tool does

Pasting company names, personal names, contacts, or API keys straight into external AIs like ChatGPT or Claude is risky. Local Mask automatically converts them into tokens before sending, then restores them in one click after you receive the AI's reply. Detection, conversion, and restoration all happen only inside your browser — your input is never sent anywhere.

02Basic usage (round-trip clipboard)

Enter text and mask it

Paste text containing secrets and press “Mask.” Names become [NAME_1], emails become [EMAIL_1], and so on.

Copy the masked text to the AI

Use “Copy masked text,” paste it into the AI chat, and ask your question. The AI never receives the real information.

Restore the AI's reply (demask)

Paste the AI reply that still contains the tokens into the “Restore” box and run it; the original terms come back instantly via the mapping table.

Discard when done

When finished, use “Discard entire mapping.” Auto-discard on closing the tab is also on by default.

03Process files in bulk

Choose a folder / files

On the “Batch files” tab, open a folder of logs etc. or drag files in.

Run batch masking

All files are processed together. On Chrome/Edge they are saved directly into the same folder with a _masked suffix; otherwise via download.

04Main detected information

Contacts & location: email addresses, phone numbers, addresses, postal codes (regex + dictionary)
Secrets & IT: credit card numbers (Luhn check), API keys/tokens (entropy analysis), passwords (label detection)
People & orgs: personal names, company/organization names (heuristics using honorifics, titles, legal forms, surname dictionary)
Custom: your own terms registered under “Detection settings”

05Frequently asked questions

QIs my entered information sent anywhere?

No. Neither your text, files, nor mapping table is sent to any external server. Everything from detection to restoration is processed inside the browser.

QWhere is the mapping table stored?

It is temporarily stored in the browser's IndexedDB and used for demasking (restoration). You can erase it with “Discard entire mapping” or the default-on “Auto-discard when the tab closes.”

QNames or company names are sometimes missed or over-detected

Names and company names are judged with contextual heuristics, so they aren't perfect. Register terms you definitely want masked in the custom term list under “Detection settings.” If detection is excessive, turn off the relevant category. Always verify with “Highlight” before sending.

Q“Open folder” doesn't work

Direct folder saving (File System Access API) requires a supported browser such as Chrome/Edge. If unsupported, use “Select files” and results are saved as downloads after processing.

QRestoration stopped working

Restoration relies on the mapping table. Tokens created after discarding the mapping, or in a different tab/device, cannot be restored. Keep each AI exchange within the same session.