ClaudeBridge 2.0

Claude for Netscape Navigator 3 on Classic Mac OS.

An HTTP server that runs on a modern Mac and makes Claude reachable from a browser built in 1996. No porting, no emulation trick — the server simply speaks the language of the older shore: HTML 3.2, ISO-8859-1, META REFRESH instead of AJAX.

The vintage machine needs nothing installed. It is a pure client.

Netscape 3 (System 7.6.1)  ──HTTP/1.0──▶  ClaudeBridge  ──HTTPS──▶  Claude API
        in Basilisk II                     on the host   ──HTTPS──▶  the modern web

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Quick start

# with git:
git clone https://github.com/LoetLuemmel/ClaudeBridge.git && cd ClaudeBridge

# without git — macOS does not ship it by default:
curl -L -o cb.zip https://github.com/LoetLuemmel/ClaudeBridge/archive/refs/heads/main.zip
unzip -q cb.zip && cd ClaudeBridge-main

python3 -m pip install -r requirements.txt   # or: uv pip install -r requirements.txt

mkdir -p ~/.config/anthropic
pbpaste > ~/.config/anthropic/api_key     # key on the clipboard, never on screen
chmod 600 ~/.config/anthropic/api_key

./start_bridge.sh                      # or: python3 claude_bridge.py

Then, in Netscape on the emulated Mac: http://10.0.2.2:8080/

On the host itself: http://127.0.0.1:8080/

Every command runs inside that directory — start_bridge.sh, netmode.py, the tests. A new terminal window starts in your home directory instead. pwd settles it.

Updating: with a checkout, git pull. From a ZIP there is no repository, so git pull answers fatal: not a git repository — download the archive again instead. Either way your API key is untouched: it lives in ~/.config/anthropic/, not in this directory.

Naming the virtual environment .venv inside the checkout avoids a confusing case: if it carries the same name as the directory, the prompt shows that word twice for two unrelated reasons. start_bridge.sh also finds .venv automatically.

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Requirements

Use python3 -m pip, not a bare pip. Current macOS ships no standalone pip command, and a virtual environment created by uv venv does not contain one either — so pip install fails with command not found even with an environment active. The module form always works.

Host — macOS with Python 3.8+, and three libraries:

Package	Used for
PyYAML	reading config.yaml
beautifulsoup4	simplifying modern HTML down to 3.2
Pillow	converting images to GIF for Netscape

Everything else is standard library. There is no framework and no Anthropic SDK — the API call goes through urllib.

Guest — Mac OS 7.5 or 7.6.1 with Netscape Navigator 3.04. Two settings, no installation:

• TCP/IP control panel → Connect via Ethernet, Configure Using DHCP Server
• Netscape → character set Western (ISO-8859-1)

Emulator — Basilisk II (68k) or SheepShaver (PowerPC) in slirp mode. Both come from the same codebase and share the preferences format, so everything here applies to either; only the file differs (~/.basilisk_ii_prefs vs. ~/.sheepshaver_prefs). See Networking below.

Real hardware is a different case: a physical Mac sits on the LAN, and slirp exists only inside an emulator process. ClaudeBridge binds loopback, so it cannot serve a real machine — that is what AppleBridge is for.

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What it does

The home page offers seven tools, each its own endpoint:

	Tool
[*]	Claude Chat	open conversation, context across rounds
[C]	Code Assistant	specialised in THINK C 7.0 for Classic Mac
[R]	Resource Generator	Rez source for MENU, DLOG, DITL, WIND, ICON
[?]	Ask & Answer	general Toolbox questions
[W]	Web Proxy	modern HTTPS sites, simplified to HTML 3.2
[F]	Shared Folder	browse the emulator's shared folder, send files to Claude
[V]	History	past questions and answers, persistent across restarts

Plus /setup for host configuration — served to loopback clients only.

Why it looks like 1996

Netscape 3 understands HTML 3.2. No CSS, no JavaScript, no modern form elements. Every design decision follows from that:

Modern web	ClaudeBridge
CSS layout	<TABLE> with BGCOLOR
AJAX / fetch	<META HTTP-EQUIV="Refresh">
UTF-8	ISO-8859-1
WebSockets	polling every three seconds

A request creates a job, starts a background thread and returns a waiting page immediately. That page refreshes onto /result/<id> every three seconds until the answer is ready — the only form of "asynchronous" this browser knows.

The web proxy

Netscape 3 speaks SSL 2.0/3.0 with 40-bit export ciphers, which the modern web no longer accepts. The proxy fetches over HTTPS, strips scripts, styles, <div> and <span>, and serves plain HTTP. Images are scaled to 500 px, reduced to an adaptive 24–64 colour palette and delivered as GIF.

Requests to loopback, private ranges, link-local, multicast and reserved addresses are refused, including through redirects — otherwise the proxy would be an open relay for anyone who can reach the port.

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Networking

ClaudeBridge 2.0 is slirp-only. The server binds 127.0.0.1 and refuses to start on any other address.

In slirp mode the guest sits behind a NAT inside the host and reaches it at 10.0.2.2, which arrives on the loopback interface. The macOS firewall can stay on and the port is never exposed to the LAN.

Bridge mode — where the guest is its own host on the network — would require binding 0.0.0.0 and switching the firewall off entirely. Avoiding that trade is the point of this version.

netmode.py switches the emulator's mode and backs up the prefs first:

python3 netmode.py show      # current mode
python3 netmode.py slirp     # NAT inside the host
python3 netmode.py bridge    # own host on the LAN (not for this version)

# SheepShaver keeps its settings elsewhere:
BASILISK_PREFS=~/.sheepshaver_prefs python3 netmode.py slirp

A mode change has two halves — this only does the host one. The guest's TCP/IP control panel has to follow. See docs/NETWORK_MODES.md.

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Configuration

config.yaml, or /setup in the browser:

Setting	Default
server.host	127.0.0.1	fixed, see Networking
server.port	8080
claude.model	claude-opus-4-5-20251101
claude.max_tokens	4096
jobs.refresh_interval	3	seconds; below 2 overwhelms Netscape 3
files.shared_folder	~/Desktop/Share	null disables the feature
proxy.block_private_networks	true	the SSRF filter
setup.require_loopback	true	who may reach /setup

The API key is not in config.yaml — that file is version-controlled. It is read from ANTHROPIC_API_KEY, then ~/.config/anthropic/api_key, then .env.

Write it with pbpaste, not with echo 'sk-ant-…' > file. The echo form puts the key on screen, into the scrollback and into ~/.zsh_history, where it stays.

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Encoding

Three separate concerns that fail in three different ways. Every one of them cost real debugging time:

Layer	Direction	Correct answer
Page output	server → browser	ISO-8859-1
HTML escaping	server → browser	decimal references only — html.escape() emits ', which Netscape 3 renders literally
Form input	browser → server	ISO-8859-1 in parse_qs — a browser submits in the document's charset, not in MacRoman

Do not change any of these without testing on a real Classic Mac.

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Tests

python3 test_claude_bridge.py     # 41 tests, unittest, no network needed

Covers path traversal, sanitizing, Netscape-safe escaping, the SSRF filter (including the redirect bypass) and the slirp-only bind rule.

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Wanted: someone to finish the native client

ClassicClient/ holds a THINK C 7.0 application — event loop, MacTCP networking, preferences, menus, Rez resources, about 2,900 lines. It would talk to the server over the JSON responses returned when the User-Agent contains ClaudeAssistant, skipping the browser entirely.

It has never been compiled, and as written it will not work. Three known problems, all in network.c:

URLEncode()	percent-encodes raw MacRoman bytes, but the server decodes ISO-8859-1 — so ü (0x9F) arrives as something else entirely
chat request	sends the field prompt, while /chat expects message
URLEncode()	writes into a fixed buffer with no length check — on a 68k without memory protection that takes the whole machine down

The server side is finished and verified: the JSON branch answers correctly, umlauts included, and can be exercised with plain curl — no vintage hardware required.

curl -H "User-Agent: ClaudeAssistant/1.0" \
     -X POST --data 'message=Hallo' http://127.0.0.1:8080/chat
# {"job_id": "1"}

What is missing is a working client. If you have THINK C 7.0 and an afternoon, this is a well-defined piece of work with a known finish line. Everything else in this repository works through the browser alone in the meantime.

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License

MIT — see LICENSE.