PromptKeep

Never lose the prompt behind an image

A local-only Chrome extension that saves AI-generated images together with the prompt that produced them. It adds a small download control to generated images on ChatGPT, Google Gemini, and Grok Imagine, then embeds the prompt in the downloaded PNG.

No backend, no accounts, no telemetry — the prompt never leaves your machine.

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What it does

PromptKeep currently supports these services:

Service	Supported pages	Extra actions
ChatGPT	Generated images on ChatGPT	Regenerate image
Google Gemini	Generated images on Gemini	Try again, Personalize
Grok Imagine	Images on grok.com/imagine/post/...	—

For every supported image:

1. Hover over the image to reveal the round P button in its top-right corner.
2. Click the button to download the full-size PNG with the original prompt embedded inside the file as metadata.
3. Find the downloaded file in your normal Downloads folder. Its name identifies the service and includes a unique ID, for example Grok_imagine_<unique-id>-ai-prompt.png.

PromptKeep does not add a visible watermark and does not change the image pixels. It keeps the original PNG data and adds the prompt metadata alongside it.

The optional quick actions use the provider's own visible controls and apply only to the specific response containing the image. If a provider changes its page layout or does not expose an unambiguous control, the affected action stays disabled; PromptKeep never calls private provider APIs.

Metadata written

Location	Field	Value
XMP (iTXt)	Iptc4xmpExt:AIPromptInformation	the original user prompt
XMP (iTXt)	Iptc4xmpExt:AISystemUsed	ChatGPT, Google Gemini, or Grok
XMP (iTXt)	Iptc4xmpExt:AISystemVersionUsed	observed model version, when visible
XMP (iTXt)	Iptc4xmpExt:DigitalSourceType	http://cv.iptc.org/newscodes/digitalsourcetype/trainedAlgorithmicMedia
PNG text (iTXt, UTF-8)	parameters	the prompt under the Stable Diffusion-compatible keyword
PNG text (tEXt)	Source	the full page URL of the conversation
eXIf	ImageDescription, Software, UserComment, XPComment	prompt and system label
caBX	—	preserved byte-for-byte; never altered or removed

parameters is written as UTF-8 iTXt, so non-Latin-1 prompts (Cyrillic, CJK, emoji) survive exactly. No Latin-1 tEXt copy is emitted, because it would turn the same prompt into mojibake.

The eXIf block is skipped when the source PNG contains a caBX chunk. ExifTool has a known bug (exiftool/exiftool#452) that makes it mis-parse a PNG containing both chunks, so the extension avoids the collision. The prompt remains fully available through XMP and parameters.

Reading the prompt back

• ExifTool / ExifToolGUI — shows PNG:Parameters, PNG:Source, and XMP-iptcExt:AIPromptInformation.
• PromptLens — a convenient local Windows application for viewing the prompt, AI system, model version, source URL, image preview, and metadata status.

PromptLens for Windows

For a more convenient way to inspect files saved by PromptKeep, use PromptLens. It is a free, local-only Windows application that opens one or more PNG files and displays:

• the original prompt;
• the AI system and model version, when available;
• the source URL;
• a preview of the image;
• the metadata reading status.

PromptLens is read-only: it never modifies the source PNG, uploads files, or saves prompts and file history. Download the latest portable Windows version from the PromptLens Releases page.

Installation

Install a release

1. Download the latest PromptKeep-v<version>-chrome.zip from the Releases page.
2. Extract the ZIP archive to a folder.
3. Open chrome://extensions in Google Chrome and enable Developer mode.
4. Choose Load unpacked and select the extracted folder.

Build from source

npm ci
npm run build

Then open chrome://extensions, enable Developer mode, choose Load unpacked, and select the generated dist/chrome directory.

Requirements

• Node.js >= 22.12.0 and npm >= 10.9.2 (development only)
• Google Chrome (Manifest V3)

Architecture

Three isolated layers keep volatile provider integrations away from the byte-level writer:

• Provider adapters (src/providers/) — versioned DOM selectors for ChatGPT, Gemini, and Grok Imagine. Each adapter pairs a rendered prompt with generated images and fails closed when identity cannot be proven.
• Extension shell (src/chrome/, src/offscreen/) — a Manifest V3 service worker validates sender origin and message schemas, fetches the asset through an allow-list, and hands the bytes to an offscreen document.
• Metadata core (src/metadata/) — a bounded, byte-preserving PNG chunk writer. It validates every chunk CRC, inserts the new chunks before the first IDAT, and never decodes or re-encodes image data through Canvas.

Limitations

• Chrome only. Manifest V3; no Firefox, Safari, or mobile builds.
• PNG only. JPEG, WebP, AVIF, and animated formats are out of scope.
• Fixtures, not live provider contracts. ChatGPT, Gemini, and Grok change their DOM without notice. When a layout changes, the affected adapter fails closed and no file is produced until its versioned selectors are refreshed.
• Quick actions depend on provider UI. Regeneration, personalization, and edit/resend are performed by clicking the provider's visible native controls. A provider layout or localization change can temporarily disable an action until its selectors are refreshed.
• parameters is iTXt. Tooling that scans only tEXt/zTXt will not see it. This is a deliberate trade-off in favour of correct non-Latin-1 prompts; XMP remains the standards-compliant channel.
• C2PA is preserved, not re-signed. When a source PNG contains caBX, the extension keeps it byte-for-byte, but the embedded signature no longer verifies for the modified file. No validity is ever claimed.
• EXIF ASCII fields transliterate. ImageDescription/Software are ASCII; non-ASCII characters become ?. The full prompt lives in the UTF-8 XMP and parameters fields.

Privacy

Everything runs locally in the browser. The extension:

• ships no remote code, uses no analytics, and sends no prompt anywhere;
• requests only storage, downloads, and offscreen, plus the exact provider hosts;
• keeps temporary operation state locally in Chrome and deletes it after completion;
• never uploads, logs, or persists the raw prompt beyond the download itself.

License

MIT