Security at thirds.ai

Last updated 13 October 2026

We treat everything you send us as untrusted: HTML, images, templates, data, and prompts. So we make your files in locked-down browsers on our own servers, keep your content out of our logs, and delete files on a schedule you can see. We don't hold SOC 2 or ISO 27001 certification, and we don't claim to.

How we make your files

Your files are made outside the website and the API, in a separate worker that runs a pinned version of Chromium. Every file gets a fresh browser context, so nothing from one file, or one customer, is left behind for the next. The worker runs as an unprivileged user on a read-only system, inside the browser sandbox and a restricted system-call profile, with hard limits on time, memory, CPU, processes, pages, assets, and output size.

The worker has no direct route to the public internet. When your design loads a remote image or font, the request goes through our own gateway. It refuses private, loopback, link-local, metadata, reserved, and malformed addresses, checks the DNS answer and every redirect again, and never passes your cookies, authorization headers, or our secrets to the host that serves the asset.

Who can read your files

Each stored file gets a random name that says nothing about your account or your original file name, and only the app's own system account can open the folders. No person at thirds.ai looks at your documents unless you ask us for help with them. Before we serve a file, we check that it is a regular file within its size limit and that its bytes match the SHA-256 fingerprint in its database record. A file that was replaced or cut short never reaches you.

A download link lasts 15 minutes, so a link that leaks stops working fast. Every finished file is served with private, no-store headers, stays out of our sitemap and feeds, and tells search engines not to index it.

How long we keep your files

• The data a file was made from is deleted as soon as the file is finished.
• A finished PDF or image stays for up to 365 days on a paid plan (Starter, Growth, or Scale), and for up to 30 days on the free plan, with credit packs only, or during the $1 Starter trial. You can pick a shorter time for any file, or delete it whenever you like.
• If your paid plan ends, files with more than 30 days left are cut to 30 days from that day, and we let you know.
• A file made in the free playground, without an account, is kept for one hour.
• Your template chat, with your messages and the drafts you accepted, stays until you delete the chat or close your account. While the AI works on a message, it makes private working copies you never see. We delete them when that message finishes.
• A prompt that made an AI image stays with the image in your account. A prompt that failed is removed after one hour.
• When you close your account, we revoke every key and session, cancel any file still in progress, and delete your files, templates, and sign-in data. If a step fails, we retry it until it's done.

After closure we keep only the limited financial, legal, and security records we must keep, such as payments and invoices. They don't include your documents unless a law specifically requires it.

Encryption in transit

Traffic to the website and the API uses HTTPS and TLS, and our server adds HTTP Strict Transport Security, so after your first visit your browser uses HTTPS only. Our own connections to the AI and analytics providers go to fixed HTTPS addresses set in our code.

Backups and recovery

Backups go to Cloudflare R2, in a bucket with a key that only the live service holds. They travel over TLS, and Cloudflare encrypts everything stored in R2 at rest with AES-256. The backup holds the database, your finished files, your saved templates, and the logos and fonts in your brand kits. It never holds the data a file was made from, your AI chat, playground files, hidden AI previews, or the keys that sign download links.

Database changes go to the backup in blocks, each within a minute of the block completing, so on a quiet day the newest changes can take longer to arrive. Finished files, templates, and brand kit files are copied every 15 minutes. We make a full database backup every 24 hours and keep the last seven, with the change blocks they need. Before a restored database can serve a template or a brand asset, a check matches every record to a file with the exact size and SHA-256 fingerprint.

Service providers

A small set of providers helps us run thirds.ai.

• Hetzner Online GmbH hosts the application, the database, and your files in Finland.
• Cloudflare runs our DNS, the bot check on public forms, and R2 backup storage.
• Resend sends sign-in and account email.
• GitHub and Google confirm who you are when you sign in with them. They tell us only your account identifier, email address, and name.
• OpenRouter and the model host it selects process what you send to the template builder and the AI image tool: your prompt and, for the template builder, your brand details and source image. That host may use this content to improve its models.
• PostHog Cloud in the EU stores the product analytics and, if you accept cookies, the session recordings that our Privacy policy describes. Recordings mask what you type and hide your designs, previews, and logos.
• Stripe runs checkout and payments on its own pages, so your card number never reaches us.

The Data processing agreement gives the full detail on these providers.

Billing and abuse limits

A file that fails costs nothing, whatever the reason. You pay only for one that finished and passed every check. Retries are safe: a request sent again with the same idempotency key returns the same file instead of making a second one. If your account causes 100 failed files in one day, from bad input, timeouts, or blocked assets, we refuse new files until the next day, so one broken script cannot tie up the service. Failures on our side never count toward that limit.

Report a security problem

Email support@thirds.ai with the subject “Security report”. Tell us the page or request ID, what the impact is, and the steps to repeat it. Please keep API keys, passwords, private documents, and live exploit data out of the email.

We read every report and tell you if we need more. The service status page shows current impact and past incidents.