Privacy Policy

Last updated: September 14, 2026

Overview

NumStack ("we", "our", "us") operates numstack.net, a set of free AI and personal-finance calculators with an optional paid API. This Privacy Policy explains what information we collect, how we use it, and the choices you have — including around advertising and analytics cookies.

Information We Collect

Automatically Collected

  • Google Analytics: We use Google Analytics (GA4) to understand pageviews, navigation flow, and device/browser type in aggregate. Google Analytics sets its own cookies to distinguish visitors; we only view this data in aggregated, non-identifying reports.
  • Google AdSense and advertising cookies: When ads are shown on NumStack, Google and its advertising partners may use cookies to serve ads based on your visits to this and other sites. Google, as a third-party vendor, uses cookies (including the DoubleClick DART cookie) to serve ads on our site. Google's use of the DART cookie enables it and its partners to serve ads to you based on your visit to numstack.net and other sites on the internet. You can read more about how Google uses this data at Google's Advertising Privacy & Terms page.
  • Server logs: Standard web server logs (IP address, browser type, pages visited, timestamps) for security and troubleshooting.
  • Cookies: Essential cookies for site functionality, plus analytics and advertising cookies as described above. See "Your Choices & Opt-Outs" below for how to control these.

Information You Provide

  • Calculator inputs: The numbers you type into a calculator (salary, token counts, request volume, etc.) are used only for the real-time calculation in your browser and are not stored or logged on our servers.
  • Email address: Your email address may come from our email signup form, or from a NumStack Pro purchase (our payment processor passes us the email tied to the subscription). We use Resend to send you confirmation and update emails. You can unsubscribe at any time using the link in those emails or by contacting us.
  • Payment information (Pro subscribers and audit purchases): Billing is handled by our payment processor, currently Stripe, which is also the merchant of record (Stripe Managed Payments). Some purchases may instead be processed by Lemon Squeezy, also as merchant of record. Whichever processes your payment receives your name, email, and payment details directly — we never see or store your card number. Via their webhook, we receive your email, subscription status, and account identifiers, which we use to activate and manage your Pro API access.
  • LLM Cost Audit intake: If you purchase the LLM Cost Audit, the information you submit on the intake form — company name, monthly spend or token volume, use cases, request shape, and any sample prompt or notes you provide — is sent to our AI provider, currently Anthropic or OpenRouter depending on configuration, so it can write the narrative portion of your report; that provider processes this text as our sub-processor under its own API terms and does not use it to train models. When OpenRouter is used, it forwards the request to the underlying model's own provider (for example Anthropic), and we configure it to refuse routing to any provider that stores or trains on prompts. We store your intake data and the finished report in NumStack's database until you ask us to delete it — email [email protected] — or for 12 months after delivery, whichever comes first. Please don't include secrets (API keys, passwords, credentials) or other people's personal data in the sample prompt or notes fields.
  • API key data: If you generate a NumStack API key (Pro or Enterprise tier), we store a one-way cryptographic hash of the key and a short preview (e.g. ns_pro_a1b2…7f8e) so we can verify requests and show it to you in your account. We do not store the full key after it is first issued to you — if you lose it, you'll need to generate a new one.
  • Contact messages: If you email us, we retain that message and any reply thread to handle your request and for our own record-keeping.

How We Use Your Data

We use the information above to:

  • Understand aggregate site usage and improve the calculators
  • Fix bugs and diagnose issues from server logs
  • Authenticate API requests against your API key
  • Send you product updates or model-request confirmations, only if you opted in
  • Show relevant advertising through Google AdSense, where enabled

Data Sharing

We do not sell your personal data. We share limited data with the following categories of third parties, each acting as an independent data controller for the data they process:

  • Google Analytics: aggregated, anonymized usage analytics.
  • Google AdSense: ad serving and, where applicable, ad personalization cookies, as described above.
  • Resend: to deliver signup confirmation and update emails to the address you provide.
  • Lemon Squeezy: our payment processor and merchant of record for NumStack Pro and the LLM Cost Audit. They receive your name, email, and payment details to process billing; we receive your email, subscription status, and account identifiers via webhook. We never see your card number.
  • Our AI provider (currently Anthropic or OpenRouter): if you purchase the LLM Cost Audit, the intake text you submit (company name, usage figures, sample prompt, notes) is sent to whichever provider is configured to generate the report narrative. When OpenRouter is used, it forwards the request to the underlying model's own provider (for example Anthropic) under a configuration that refuses routing to providers that store or train on prompts — see "LLM Cost Audit intake" above.
  • Railway: our hosting provider, which processes data as part of running the application.
  • Law enforcement: only if required by valid legal process.

Your Choices & Opt-Outs

You can control analytics and advertising cookies:

  • Manage or opt out of personalized Google ads at Google Ads Settings.
  • Opt out of interest-based advertising from participating companies at aboutads.info (US) or youronlinechoices.eu (EU).
  • Install the Google Analytics Opt-out Browser Add-on to prevent Google Analytics from using your data on any site.
  • Use your browser's cookie settings to block or delete cookies at any time.
  • Unsubscribe from emails using the link in any message we send, or by contacting us.

Consent and Cookie Choices

On your first visit, a banner at the bottom of the page asks you to accept or reject non-essential cookies (analytics and, where advertising is enabled, ad personalization). We use Google Consent Mode v2 to carry your choice through to Google Analytics and AdSense: until you accept, analytics and advertising storage stay denied by default, and nothing beyond strictly necessary cookies is set.

  • Accept all: grants analytics and (where ads are enabled) advertising storage and personalization.
  • Reject non-essential: keeps analytics and advertising storage denied; only cookies required for the site to function are used.
  • Your choice is stored in your browser's local storage (not a cookie) so the banner doesn't reappear on every page. It is not synced to our servers or tied to your identity.
  • To change your choice later, click Cookie settings in the footer of any page — this clears your stored choice and reshows the banner immediately.

Data Retention

Roughly, and as a matter of policy rather than a technically enforced schedule: we retain data only as long as it serves the purpose it was collected for.

  • Email addresses (signup list): retained until you unsubscribe using the link in any email we send, or ask us to remove you.
  • API usage logs and signup events: we retain these for up to 12 months for security, abuse detection, and troubleshooting, then delete or aggregate them.
  • Contact emails: retained as long as needed to respond to and resolve your request, and for our own record-keeping afterward.
  • Server logs: retained for up to 12 months for security and troubleshooting.
  • Consent choice: stored in your browser's local storage until you clear your browser data or use the "Cookie settings" link to reset it — we don't hold a server-side copy.

You can request deletion of your data at any time — see "Your Rights" below.

Security

We use HTTPS encryption on all pages. API keys are never stored in plain text — only a one-way hash and a truncated preview are retained after issuance. That said, no method of transmission or storage is 100% secure, and we can't guarantee absolute security.

Your Rights

Depending on where you live, you may have the right to:

  • Request what data we have about you
  • Request correction or deletion of your data
  • Opt out of analytics and advertising tracking (see above)
  • Unsubscribe from emails at any time
  • Request a copy of your data in a portable format

To exercise these rights, email [email protected] or visit our Contact page.

Third-Party Services

Affiliate Links

Some calculator pages link to third-party vendors (for example, GPU cloud providers, vector database vendors, and tax software) and some of those links may be affiliate or referral links. If you sign up or make a purchase through one of those links, we may earn a commission — this does not change the price you pay. Affiliate links are marked with a rel="sponsored" attribute. We do not share your personal data with these vendors; clicking through simply takes you to their site.

Children's Privacy

NumStack is not directed at children under 13, and we do not knowingly collect personal information from them.

Changes to This Policy

We may update this policy from time to time. The "Last updated" date at the top reflects the most recent revision, and significant changes will be posted here.

Contact

Questions about this policy? Email [email protected].