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Postcard uses Google Gemini to power its corroboration and auditing agents. A Gemini API key is required to start a new forensic analysis. Cached results are always served for free — no key needed.

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Get a free Gemini API key

Google AI Studio offers a free Gemini API key with no credit card required.
1

Open Google AI Studio

Go to aistudio.google.com/app/apikey and sign in with your Google account.
2

Create an API key

Click Create API key and copy the generated key. Keep it somewhere safe — you won’t be able to view it again after closing the dialog.
3

Open Postcard Settings

Navigate to postcard.fartlabs.org and click Settings in the navigation bar.
4

Paste and save your key

Paste your API key into the Google AI API Key input field and click Save Key. The UI confirms the key is configured.
Your API key is stored in a browser cookie named postcard_api_key with a 30-day expiry. When you submit a URL for analysis, the key is included in the POST request body as userApiKey and passed to the Postcard server, which then uses it to call the Google Gemini API. The key is not stored server-side — it is only used for the duration of the analysis request.

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How the key is used

When you submit a URL for analysis, your browser reads the postcard_api_key cookie value and includes it in the POST request body as userApiKey. The Postcard server receives this key and passes it to the Google Gemini SDK when calling the corroboration and auditing agents. If no userApiKey is present in the request and no server-side default is configured via GOOGLE_GENERATIVE_AI_API_KEY, the pipeline will not start.

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Managing your key

From Settings you can:
  • Save Key — stores a new or updated key in the cookie
  • Test Key — sends a test POST request to /api/postcards with your stored key to confirm it is accepted
  • Clear — removes the cookie from your browser

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Rate limits on the free tier

The free Gemini API tier has rate limits. If you hit them, the pipeline will fail with an error from the Gemini API. The Postcard UI displays the failure state with the error message. Wait a short period and retry, or consider upgrading to a paid Gemini tier for higher throughput.

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For self-hosters: server-side default key

If you are running Postcard yourself, you can set a server-side default Gemini API key via the GOOGLE_GENERATIVE_AI_API_KEY environment variable in your .env file: 
GOOGLE_GENERATIVE_AI_API_KEY=your-key-here
When this variable is set, the pipeline uses it as a fallback if no userApiKey is provided in the request. This is useful for private deployments where you want all users to share a single key without requiring individual configuration.
A userApiKey supplied in the POST request body always takes precedence over the server-side GOOGLE_GENERATIVE_AI_API_KEY environment variable.

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