Claude S40

Chat with Claude on a 2007 Nokia. Claude S40 is an unofficial Claude client for Nokia Series 40 phones (Java ME, CLDC 1.1 / MIDP 2.0), plus the small Go server it talks to. Type on the keypad, get Claude's answer on a 240x320 screen: with today's news, weather and exchange rates from web search, long answers you can page through, and a UI in Turkish or English.

Video: Claude S40 on a Nokia 6300, on X

Features

On the phone

• Chat with bubbles, timestamps and a typing indicator that counts the seconds. Replies keep their paragraphs and lists (dots, numbers, hanging indent).
• Web search for news, weather, rates: Claude searches on the server, the phone's 2007 browser is not involved. Sources are listed under the reply.
• Reading mode (key 7): one reply full width, page by page, whole lines only, page number and progress line. It keeps its place when you change the text size (key 9) or load the rest, and keeps the backlight on.
• Long replies in parts: "0 · Show the rest" fetches the next part from the server for free; Claude is not asked again.
• Message actions: select a message with 1/3, press the centre key: shorten, explain more simply, translate, ask about it, open it in the editor. They only fill in the editor; nothing is sent until you press Send.
• Earlier chats from the server, continue any of them; pin the ones you want to keep at the top (kept until unpinned), delete or search all chats (no Turkish letters needed: "sise" finds "şişe"); optional offline copy of the last chat.
• Save to phone: a reply as a .txt file (memory card if there is one), readable later without the network under "Saved".
• Calendar and to-do: ask "add to my calendar: dentist tomorrow at 3" and the reply carries a ready entry; the centre key opens a prefilled form, and only your "Save" writes it to the phone's own calendar or to-do list. Works from any message too.
• Your notes for Claude (Settings): "I'm Emir, I live in Istanbul, keep it short" is sent with every message.
• Data usage: requests and approximate kilobytes today and in total.
• 20 quick prompts (search the web, weather, translate, reply to a message, add to my calendar, summarize, fix my writing, ...).
• Setup wizard on first start: language, server address, connection test, pairing with a 6-digit code (no long code to type).
• Keypad-first: every screen works with the keypad; a Shortcuts screen lists every key. Retry after an error is one key and never charges twice.
• Look and feel: light and dark theme, three text sizes, start-up animation and jingle, reply chime, vibration and backlight. Texts are fitted to the screen and checked from 128x160 to 320x240.

On the server

• One Go binary / Docker image that speaks TLS 1.0 to the phone with a certificate from your own private CA, and modern HTTPS to the Claude API.
• Per-device access tokens through pairing, daily request, token and web-search limits, no automatic retries of paid calls.
• SQLite for chats (30 days, pinned ones until unpinned), search over them, admin API on localhost only.

Screens

Screenshots are from the FreeJ2ME emulator in the app's test mode (the "[Test mode]" replies are fake and cost nothing; the emulator reports no calendar API, so the harness turns the calendar actions on for these screens and never saves); the cover is a drawing. Start-up animation: docs/images/splash.gif.

Unofficial side project. Not made, endorsed or supported by Anthropic or Nokia. See TRADEMARKS.md.

Tested on a Nokia 6300 (RM-217, firmware V06.60). Other Series 40 phones (CLDC 1.1 / MIDP 2.0, 240x320) may work but are untested.

How it works

Nokia (Java ME app) --HTTPS: TLS 1.0, RSA, no SNI, cert from YOUR private CA--> claude-s40-server --HTTPS--> Claude API
                                                                                     |
                                                                              SQLite (Docker volume)

A 2007 phone cannot speak modern HTTPS: the Nokia 6300 offers only TLS 1.0 with RSA key exchange, sends no SNI, and its root store stops around 2008. Public clouds (including Cloudflare) refuse that handshake. So the server terminates TLS itself with a certificate from a private root CA that you put on the phone once. Details and measurements: docs/ARCHITECTURE.md.

What's inside

Get it

git clone https://github.com/emir/claude-s40.git
cd claude-s40

Quick start

Full guide: docs/SETUP.md. In short:

1. A Docker host with a public IPv4 and TCP 443 (a $4-6/month VPS is enough).
2. server/scripts/pki.sh ca ~/.config/claude-s40/pki and server/scripts/pki.sh server ~/.config/claude-s40/pki <server-ip>.
3. server/deploy/push.sh root@<server-ip> --execute (starts in test mode, no API cost).
4. echo GATEWAY_URL=https://<server-ip> > app/app.local.properties && make -C app, then install app/dist/ClaudeS40.jad/.jar on the phone.
5. Put the root CA on the phone (server/deploy/serve-ca.sh, compare the fingerprint).
6. On the phone the setup wizard walks through the connection test and pairing; approve the code with server/deploy/admin.sh root@<server-ip> pair <code>.
7. server/deploy/set-key.sh root@<server-ip> and S40_MOCK=0 server/deploy/push.sh root@<server-ip> --execute to go live.

Development

make test          # server: go vet + go test -race; app: build + 44 checks + reproducibility
make -C app        # phone app only (downloads pinned build tools to app/.deps)
make -C server test

Requirements: Go 1.26+, JDK 11+, Python 3 with Pillow, Docker (for deployment), OpenSSL or LibreSSL.

Privacy and cost

• The Claude API key lives only on your server. The phone gets a per-device, revocable access token through pairing.
• Chats are stored on your server for 30 days after the last message; pinned chats until you unpin or delete them. The phone keeps the last chat only if you turn on "Keep last chat on phone"; replies you save and calendar entries you add stay on the phone. Your notes for Claude are stored on the phone and sent with each message (never logged).
• The setup (server address, access code, notes) is also kept in a file on the memory card so a new build needs no new pairing; revoke the device if the card leaves your hands, or use Settings > Reset setup. Logs contain no message text.
• Every message is a Claude API call billed to your key. The server enforces per-device daily request, output-token and web-search limits and never retries a paid call automatically. Web searches are billed per search and their results count as input tokens. Set a spending limit in the Claude Console.

License

MIT, see LICENSE. Copyright (c) 2026 Emir Karşıyakalı. Build-time tools are downloaded, not bundled (ECJ: EPL-2.0, ProGuard: GPL-2.0, MicroEmulator API stubs: LGPL); none of them end up in the phone app. The optional emulator harness app/emu/EmuShot.java links against FreeJ2ME (GPL-3.0), which is not included.