NoteStack Privacy Policy
Last updated: July 2026
The short version: NoteStack reads your Substack data using your existing browser session. Your Notes, profile, and subscriber stats are stored locally on your device and never leave your browser. A small set of features — AI generation and subscription license validation — send a strictly limited, disclosed set of data to our own relay server to work at all. This page lists exactly what, and why.
What stays entirely on your device
- Your Substack profile (name, username, profile photo)
- Your Notes (text, timestamps, like/restack/comment counts)
- Your publication subscriber stats (if available)
All of the above is stored exclusively in your browser's local IndexedDB storage (database name NoteStackDB). You can inspect or delete it at any time via Chrome DevTools → Application → IndexedDB. None of it is ever transmitted anywhere by the Dashboard, Heatmap, Note DNA, Trends, Streak Tracker, or CSV Export features — those work entirely from data already synced to your device.
What is sent to our relay server, and why
NoteStack operates one relay server (api.stacktreelabs.com) that a small number of features call. Nothing is sent to it unless you actively use one of these features:
| Data sent | When | Why |
|---|---|---|
| Your Substack user ID (a numeric account identifier, not your name or email) | Every Ghostwriter or AI Post Coach request | To enforce per-account usage limits — this keeps the feature financially sustainable. |
| The text of your Notes, or a compact summary of your own Notes' performance stats | Only when you click “Train,” “Generate,” “Score,” “Diagnose,” or “Get my suggestion” | Sent to Anthropic's API (our AI provider) server-side, solely to produce that one response. Never sent anywhere except our relay and Anthropic. |
| Your license key, or a customer/subscription identifier issued by Polar, our payment processor | When validating or activating a Starter or Pro subscription | To confirm your subscription and tier — we never see your card details, entered directly on Polar's own hosted checkout page. |
That is the complete list. No other feature sends any data anywhere.
No analytics, no tracking, no fingerprinting
NoteStack does not use analytics tools, crash reporters, telemetry, or any form of device/browser fingerprinting. We do not attempt to identify or track you across sessions, devices, or installs beyond the Substack user ID described above, which is used solely for the usage-limit purpose stated.
Network requests, in full
- Substack API (
substack.com) — using your existing login session cookies, exactly as if you were using the Substack website. - Our relay (
api.stacktreelabs.com) — only for Ghostwriter, AI Post Coach, draft scoring, flop diagnosis, and subscription licensing, only sending the data described in the table above. - Our payment processor (
polar.sh) — only if you open the Starter or Pro checkout page, which is Polar's own hosted page. We never see your payment details.
No other domain is ever contacted.
Your controls
- Uninstalling NoteStack or clearing its local storage deletes everything in “What stays entirely on your device” above.
- Usage limits for Ghostwriter/AI Post Coach are tied to your Substack account (not local storage), specifically so clearing storage can't be used to exploit the underlying cost of those features — everything else stays fully under your control.
Third-party services
- Substack— NoteStack reads data from Substack using your session. Substack's own privacy policy applies to your account and data on their platform.
- Polar — our payment processor and merchant of record for NoteStack Starter and Pro subscriptions. It handles checkout and billing, and its own privacy policy and buyer terms apply to that transaction.
Children's privacy
NoteStack is not directed at children under 13 and does not knowingly collect any information from children.
Changes to this policy
If this policy changes materially, we will update the “Last updated” date above and note the change in the Chrome Web Store listing.
Contact
Questions about this privacy policy? Contact us at stacktreelabs@gmail.com.