xpharness

A tiny agentic coding harness — a stripped-down Claude Code — that runs in PowerShell 2 on Windows XP. It gives the model a set of tools (run/read/ write/edit files, grep/find, native C compilation, web search, ASCII-art, and more — see below) and loops tool calls until it produces a final answer, just like a modern agent harness. It can also run small models fully offline.

Hobby / educational project. No warranty. It talks to a paid API (your key, your spend) and ships an end-of-life TLS stack (OpenSSL 1.0.2) for the XP transport — don't push anything sensitive through it.

Quickstart

On a modern Linux/mac box (XP can't fetch these over TLS) with curl, python3, and gcc-mingw-w64-i686:

git clone https://github.com/<you>/xpharness && cd xpharness
./setup.sh                       # fetch curl/TCC/models, build the XP engines
cp config.sample.ps1 config.ps1  # then paste your Anthropic API key into it

Copy the folder to the Windows XP box (SFTP/USB). On XP, once (see Prerequisites): install .NET 3.5 and the VC++ 2005 redistributable, then:

powershell -ExecutionPolicy Bypass -File test-curl.ps1 sk-ant-...   :: prove TLS 1.2 works
powershell -ExecutionPolicy Bypass -File harness.ps1                :: launch

…or just double-click xpharness.bat (it sets the working directory and launches the harness for you). Want the Clippy icon on it? Make a desktop shortcut to xpharness.bat, then Properties → Change Icon → browse to images\clippy-xp.ico.

Demo

Launch greets you with a banner and a familiar paperclip:

 ### #    ### ###  ###  #  #      #  # ###
#    #     #  #  # #  #  ##        ##  #  #
#    #     #  ###  ###    #  ####   #  ###
#    #     #  #    #      #        ##  #
 ### #### ### #    #      #       #  # #
 __
/  \
|  |
@  @
|| ||
|| ||
|\_/|
\___/

It looks like you're coding on Windows XP. Want some help?
ready. Model: claude-sonnet-4-6

Then it's an agent loop with real tools — here it writes, compiles, and runs C natively on XP via the bundled Tiny C Compiler:

[C:\dev]
you: make a folder fib, write a C program that prints the first 15 Fibonacci
     numbers, compile it and run it

  -> make_dir      MKDIR fib                       allow? [y/N]: y
  -> write_file    WRITE 249 chars to: fib\fib.c   allow? [y/N]: y
  -> compile_run   COMPILE & RUN C (249 chars)     allow? [y/N]: y

  compiled OK, exit 0
  0 1 1 2 3 5 8 13 21 34 55 89 144 233 377
  [tokens] call: in 3459 out 185 | session: in 15491 out 666

Other things to try: /models local-tl (chat with a 1.1B model fully offline), banner "HELLO", image_to_ascii on a .bmp, /paste to send your clipboard.

The TLS problem (and why this works)

Windows XP's TLS lives in the OS crypto library (SChannel), which tops out at TLS 1.0. The Anthropic API requires TLS 1.2. PowerShell's WebClient / Invoke-WebRequest go through SChannel, so they cannot connect — no setting fixes this, because the OS literally can't speak TLS 1.2.

The fix is the same trick the Supermium browser uses on XP: bring your own crypto. We shell out to a curl build that bundles its own OpenSSL instead of using SChannel. That curl can negotiate TLS 1.2 on an OS from 2001.

Prerequisites

1. .NET Framework 3.5 on the XP box — needed for JSON (System.Web.Extensions / JavaScriptSerializer). PowerShell 2 has no ConvertTo-Json.
2. Microsoft Visual C++ 2005 Redistributable — bin\curl.exe links against msvcr80.dll, which is NOT on a stock XP install. Without it curl won't even start ("application failed to initialize" / missing DLL). Install the VC++ 2005 redist (vcredist_x86.exe) on the XP box. This is the one non-obvious gotcha.
3. The binaries/models are not committed (size + licensing). Run setup.sh on a modern machine to fetch and build them — see Building from a clone.
   • curl: 7.42.1 + OpenSSL 1.0.2u (static, TLS 1.2) from OmegaAOL/curl-windows98.
   • cacert.pem: Mozilla CA bundle from https://curl.se/ca/cacert.pem.

Building from a clone

The repo holds source only. On a modern Linux/mac box (XP can't reach these hosts over TLS), with curl, python3, and the 32-bit MinGW cross-compiler (sudo apt install gcc-mingw-w64-i686):

./setup.sh              # curl, TCC, TinyStories models, build engines
./setup.sh --tinyllama  # also export TinyLlama-1.1B int8 (needs torch; ~2.2GB)

Then copy config.sample.ps1 config.ps1, add your API key, and SFTP the whole folder to the XP box. Licenses for the fetched components: see THIRD-PARTY-NOTICES.md.

Burn it to a DVD (optional)

./make-iso.sh    # -> xpharness.iso (full bundle is ~1.6GB, needs a DVD)

The ISO ships an autorun.inf so the disc shows the Clippy icon and double-clicking the drive launches the harness. Your config.ps1 is not included — on the XP box, put it at %USERPROFILE%\xpharness\config.ps1 (the harness looks there when running from read-only media). Burn the .iso as a disc image (ImgBurn on XP, or "Burn disc image" on Win7+), not as a file copy. The big local-tl model is slow off optical media — copy llm\ to the HDD if you want to use it.

Setup

xpharness\
  harness.ps1
  xpharness.bat       (double-click launcher)
  extras.ps1          (retro flair: banner + image_to_ascii)
  test-curl.ps1       (step-1 TLS check)
  config.sample.ps1
  config.ps1          (you create this)
  bin\
    curl.exe          (bundled)
    cacert.pem        (bundled)
  tools\
    tcc\              (bundled Tiny C Compiler - enables compile_run)
  llm\                (optional offline models - see llm\README.md)

SFTP the whole folder to the XP box, then:

1. Install the VC++ 2005 redist (see prerequisites) so curl.exe can run.
2. Step 1 — prove TLS works (do this first):

   powershell -ExecutionPolicy Bypass -File test-curl.ps1 YOUR_API_KEY
   

   You want to see "tls_version":"TLS 1.2" from the howsmyssl check and a JSON model list from Anthropic. If so, the hard part (TLS on XP) is solved.
3. Step 2 — run the harness: copy config.sample.ps1 → config.ps1, paste your ApiKey, then:

   powershell -ExecutionPolicy Bypass -File harness.ps1
   

Slash commands (typed at the you: prompt)

Command	Does
/help	list commands
/paste	submit clipboard contents as the prompt (good for multi-line)
/multi	enter multi-line input manually (end with a line of just .)
/models [name]	switch: sonnet/haiku/opus (API), or local/local-110m/local-tl (offline)
/cwd	show the current working directory
/cd <path>	change the working directory
/tokens	session token + cost totals
/tools	list available tools
/reset	clear the conversation (keeps the session running)
/save [file]	save a resumable session as JSON (default xph_session.json)
/load [file]	restore a saved session and keep going (default xph_session.json)
/export [file]	save a readable transcript (default xph_transcript.txt)
exit / quit	leave

Tools the model can call

• run_command — run a cmd.exe command (with timeout, see below)
• read_file — read a text file; supports offset/limit line windows and line_numbers for big files
• write_file — create / overwrite a file (keeps a .bak, shows a diff preview)
• edit_file — surgical search-and-replace (old_text→new_text, unique unless replace_all; diff preview + .bak). Preferred over write_file for changes.
• undo_file — restore a file from its .bak
• grep — search file contents for a pattern (recurse for trees)
• find — find files by name pattern (e.g. *.ps1)
• list_dir — list a directory
• set_cwd — change the working directory for all later tools (persists)
• make_dir — create a directory (and any missing parents)
• compile_run — compile and run C natively via the bundled Tiny C Compiler
• detect_toolchains — report available compilers/interpreters (tcc, gcc, cl, python, ...)
• banner — big ASCII-art text (offline, built-in font)
• image_to_ascii — render an image file as ASCII art (offline, pure PS2 + GDI+)
• web_search — Exa web search over curl.exe (TLS 1.2). Set ExaApiKey in config to enable it; without a key the tool returns a "not configured" message and the model falls back to its own knowledge. Great for current docs and APIs the (old) model context may not have.

Known limitations / edge cases

• Streaming — on by default (Stream), the answer prints as it arrives. It's read from curl's raw stdout decoded as UTF-8 directly (XP can't set a UTF-8 console codepage), so non-ASCII stays correct. Set Stream=$false for the simpler file-based request.
• Markdown rendering — RenderMarkdown approximates bold/italic/headings/ lists with the 16 console colors (no true bold/italic exists in the XP console). Set $false for plain teal text.
• Command timeout — run_command kills anything exceeding CommandTimeoutSec (default 30s) and returns partial output, so a hung or interactive program won't freeze the loop. Bump it in config for slow builds.
• Token/cost readout — each turn prints input/output tokens and a session running total (the agent loop makes several API calls per turn, all counted). Set PriceInPerMTok / PriceOutPerMTok in config to also show a ~$ estimate.
• Encoding — files are written UTF-8 no-BOM. Old XP tools may expect the system codepage; adjust $Utf8 in harness.ps1 if you see mojibake.
• JSON size — capped at 64 MB (MaxJsonLength). Huge files via read_file will blow the context anyway; prefer run_command with find/type.
• Confirmation prompts — Confirm = $true in config asks before every command/write. Set $false to let it run unattended (riskier).
• .NET 3.5 missing? If LoadWithPartialName fails, the harness can't do JSON. Either install .NET 3.5 or replace the JSON helpers with a hand-rolled parser.

How it works

REPL (you type)
   -> add user message
   -> Send-ToClaude: serialize convo to JSON, POST via curl over TLS 1.2
   -> parse response
        - print text blocks
        - if stop_reason == "tool_use": run each tool, append tool_result, loop
        - else: done, back to prompt

All state is the $messages array — the full conversation is resent each turn, which is exactly how the real thing works under the hood.

Startup shows a CLIPPY-XP ASCII banner and a paperclip in BannerColor (config; default Green — the XP console only has 16 colors, so avoid Blue and DarkYellow, which look bad). Type /paste to send your clipboard, /multi for manual multi-line input.

Licensing

The original harness code is MIT (LICENSE). setup.sh downloads third-party components (curl/OpenSSL, Tiny C Compiler, llama2.c, TinyStories, TinyLlama, the Llama-2 tokenizer) from their upstream sources under their own licenses — they are not redistributed here. See THIRD-PARTY-NOTICES.md. Notably TCC is LGPL and the tokenizer is under Meta's Llama 2 license; the download-on-setup approach keeps you from being their redistributor.

config.ps1 (your API keys) is git-ignored — commit only config.sample.ps1.