Notes to Kindle

Send your Obsidian notes to your Kindle as EPUB, straight from the Obsidian desktop app.

Unofficial integration. This app was not created or endorsed by Amazon. It is not sponsored, approved, or otherwise affiliated with Amazon, and it makes no claim of official status. Kindle and Send to Kindle are trademarks of Amazon.com, Inc. or its affiliates.

What it does

Notes to Kindle takes the current note, converts it to an EPUB, and delivers it to your Kindle over Wi-Fi as a personal document. It uses the note title and the default author configured in the plugin settings.

What's new in 0.1.6

• Detects HTTPS images in Markdown inline and reference-style image tokens, including images inside expanded embedded notes. Raw HTML, code spans, and fenced code are never treated as image requests.
• Asks before making any remote image request. Approval applies only to the current send and is never saved; choosing Skip remote images keeps the safe alt-text fallback.
• Downloads at most 20 unique remote URLs through an SSRF-hardened transport: public IPs only, pinned DNS answers, isolated sockets, strict TLS hostname verification, same-origin redirects only, a 15-second deadline for the whole remote-image phase, and bounded identity-encoded responses.
• Sends no cookies, Amazon credentials, or authorization headers to image hosts. Those hosts still receive your IP address and the requested URL, including any path or query string already present in the note.
• Validates remote bytes through the same bounded image pipeline as local files. JPEG, opaque PNG, and static GIF are packaged directly. Remote transparent PNG and WebP are omitted because their browser conversion cannot be cancelled safely within the remote-phase deadline; failures degrade to alt text without aborting the send.
• SVG remains disabled for the planned 0.1.7 work.

What's new in 0.1.5

• Converts vault-local transparent PNG and static WebP images to JPEG entirely inside Obsidian before building the EPUB.
• Flattens transparency onto a white background and rejects APNG or animated WebP before browser decoding.
• Hashes, deduplicates, budgets, and revalidates the converted JPEG bytes using the existing image security pipeline.
• Converted PNG/WebP metadata is not intentionally copied; local images included without conversion may still retain EXIF, GPS, thumbnails, or color profiles.
• Remote images remain disabled in this release, and SVG remains disabled for the planned 0.1.7 work.

What's new in 0.1.4

• Includes validated vault-local JPEG, opaque PNG, and static GIF images in the EPUB.
• Resolves images relative to both the current note and embedded notes, with SHA-256 deduplication and bounded resource limits.
• Shows a privacy preflight with image count and total size before original bytes — which may retain EXIF or GPS metadata — are sent to Amazon.
• Keeps SVG, WebP, transparent images, animated GIFs, and remote images out of the EPUB; they degrade to visible omission markers or safe alt text and remote images are never downloaded.
• Supports Amazon's exact current CAPS upload endpoint (zme-caps.amazon.com) without broadening trust to arbitrary amazon.com hosts.
• Verified with 201 automated tests, EPUBCheck 5.3.0, and end-to-end delivery on a physical Kindle.

See the Notes to Kindle 0.1.4 release for downloadable artifacts and release notes.

Important: how the send works

There is no public Send to Kindle API. This plugin talks to Amazon's undocumented, internal Send to Kindle endpoints and reuses protocol and client identifiers associated with Amazon's official desktop client. It registers a synthetic device in your Amazon account so documents can be delivered to it.

What that means in practice:

• The integration can stop working without notice if Amazon changes, restricts, or removes those endpoints.
• Using an unofficial integration against internal Amazon services may carry risk to your Amazon account and may conflict with Amazon's terms of service.
• Nothing here is legal advice, and this disclaimer does not remove or reduce any risk you take on.

You stay in control. Authentication only happens when you click Authenticate, and each note is sent only when you run the send command. Every request is initiated by you, from your machine. By authenticating and by sending notes, you accept the risk of this unofficial integration.

Data and privacy

What leaves your machine on each send:

• The note's title and the author name you configured.
• The complete note content, including the expanded text of embedded notes up to a nesting depth of 3.
• Approved local and remotely downloaded JPEG, opaque PNG, and static GIF image bytes referenced by those notes, plus JPEG output produced locally from transparent PNG and static WebP inputs. Images included without conversion can retain embedded metadata such as EXIF, camera details, thumbnails, ICC profiles, or GPS location; converted inputs do not intentionally copy source metadata. The plugin confirms the count and total size before sending them.
• The generated EPUB built from that content.
• The EPUB file size and the serial numbers of the selected destination devices.
• Protocol metadata required by Amazon's internal service, including the synthetic device identifier, access/authentication tokens, and cryptographic request signatures. The RSA private key itself is not sent back to Amazon.

Where it goes:

• api.amazon.com: OAuth token exchange.
• firs-ta-g7g.amazon.com: synthetic device registration.
• stkservice.amazon.com: the send-to-Kindle delivery request.
• A presigned HTTPS upload URL on an AWS S3 endpoint (s3.amazonaws.com or a supported regional, virtual-hosted, dual-stack, or legacy S3 form) or Amazon's exact CAPS upload host (zme-caps.amazon.com). Arbitrary Amazon/AWS subdomains, userinfo, IP literals, redirects, and non-default ports are rejected.
• If you approve remote images for a send, each HTTPS image host shown in the confirmation receives a direct request from your machine. The host sees your IP address, the requested path/query, and the plugin user agent. The plugin sends no cookies, Amazon credentials, referrer, or authorization header. DNS answers are pinned to isolated connections, any private, local, special-purpose, or mixed public/private answer is rejected, and redirects to another origin are blocked.

What stays local:

• Nothing is routed through a developer-operated server. There is no backend, no telemetry, and no analytics.
• Your Amazon tokens and the plugin's RSA private key are stored in your OS keychain via Obsidian's secretStorage, never in plaintext files.
• The EPUB is written to a private temp directory (mode 0700, file mode 0600) and removed in the normal send cleanup path. An abrupt process or system crash can leave that private temporary file behind until the operating system or user removes it.

Disconnect. Disconnect in settings only clears the locally stored credentials. It does not deregister the synthetic device. To revoke access server-side, remove the device from Amazon's Content & Devices page.

Capabilities

• Converts the current Markdown note to EPUB with a clean stylesheet.
• Expands embedded notes (![[other note]]) up to a nesting depth of 3.
• Flattens callouts and normalizes wikilinks.
• Renders checkboxes, highlights (==text==), and safe links.
• Includes vault-local JPEG, opaque PNG, and single-frame GIF images referenced with Obsidian embeds or Markdown image syntax. Transparent PNG and static WebP inputs are flattened onto white and converted locally to JPEG. Images are resolved relative to the note that contains them, validated, deduplicated, and confirmed before sending.
• With per-send approval, includes HTTPS JPEG, opaque PNG, and static GIF resources referenced by Markdown inline or reference-style image tokens. Remote resources share the local image limits: 10 MiB per response, 50 MiB total, 100 unique packaged assets, and 20 unique remote URLs.
• Not included: HTTP or non-public remote resources, remote transparent PNG or WebP, APNG, animated WebP/GIF, SVG, BMP, TIFF, HEIC, AVIF, raw HTML images, CSS backgrounds, Canvas/PDF pages, or plugin-rendered diagrams. Unsupported resources degrade to alt text or an omission marker.
• Escaping: raw HTML is escaped rather than executed. Links only keep safe schemes (http:, https:, mailto:); everything else is neutralized.

Requirements

• Obsidian desktop (this plugin uses Node and Electron APIs, so it does not run on mobile).
• Obsidian 1.11.4 or newer (for app.secretStorage).
• An Amazon account with at least one Kindle device or the Kindle app installed.

Install

1. Copy the release artifacts into <Vault>/.obsidian/plugins/notes-to-kindle/. Only main.js and manifest.json are required; styles.css is optional and is currently omitted.
2. In Obsidian, open Settings → Community plugins, enable "Notes to Kindle", and allow third-party plugins if prompted.

Installing over the deprecated send-to-kindle (0.1.1) folder? See Migrating from send-to-kindle (0.1.1).

For development:

bun install
bun run dev      # watch mode
bun run build    # production build

Migrating from send-to-kindle (0.1.1)

Releases before 0.1.2 shipped under the plugin id and install folder send-to-kindle. The plugin id is now notes-to-kindle; send-to-kindle is deprecated history and is kept only for migration compatibility. Upgrading from 0.1.1:

1. Close Obsidian.
2. Rename the plugin folder from <Vault>/.obsidian/plugins/send-to-kindle/ to <Vault>/.obsidian/plugins/notes-to-kindle/. This preserves your settings (data.json), because Obsidian stores plugin data inside the plugin folder.
3. Reopen Obsidian and enable "Notes to Kindle" if it shows as disabled. If Obsidian still lists the old send-to-kindle entry, remove it — the new folder replaces it.
4. Reassign any hotkeys bound to the old command namespace. The command IDs themselves (send-note, authenticate-amazon) are unchanged, but Obsidian prefixes them with the plugin id, so they are now notes-to-kindle:send-note and notes-to-kindle:authenticate-amazon instead of send-to-kindle:.... Rebind them in Settings → Hotkeys.
5. No reauthentication is needed. The plugin keeps reading the exact SecretStorage keys send-to-kindle-credentials and the legacy stk-credentials, so credentials saved by 0.1.1 load as before, and Disconnect still clears both keys.

Usage

1. Open Settings → Community plugins, enable "Notes to Kindle".
2. In the plugin settings, click Authenticate. An isolated, sandboxed Electron window opens for the Amazon login. The plugin does not open your system browser and does not use a local HTTP callback.
3. Open any note and run the command Send current note to Kindle.

Architecture

Module	Responsibility
src/main.ts	Plugin entry, command registration, lifecycle, OAuth window
src/settings.ts	Settings UI
src/stk/client.ts	STK client: device registration, delivery
src/stk/credentials.ts	SecretStorage-backed credential handling
src/stk/oauth.ts	OAuth2 PKCE flow (sandboxed Electron BrowserWindow)
src/stk/redirect.ts	Strict validation of the Amazon OAuth redirect
src/stk/signer.ts	RSA PKCS#1 v1.5 request signing
src/stk/upload.ts	Presigned S3 URL validation
src/stk/presign-upload.ts	Bounded, timeout-aware presigned upload transport
src/stk/user-agent.ts	Client identifier handling
src/obsidian-extract/extract.ts	Markdown preprocessing for Kindle
src/images/validate.ts	Bounded JPEG, PNG, and GIF structural validation
src/images/webp.ts	Bounded static WebP container inspection
src/images/convert.ts	Local Chromium raster conversion to opaque JPEG
src/images/remote-fetch.ts	Consent-gated, SSRF-hardened HTTPS image transport
src/images/preflight.ts	Remote-download consent and final image-send confirmation
src/epub/builder.ts	EPUB generation
src/epub/render.ts	Hardened Markdown rendering
src/epub/temp.ts	Secure temp file handling

License

MIT. See LICENSE and THIRD_PARTY_NOTICES.md.