fixen

You already talk to an LLM all day. fixen turns it into your personal proofreader: one tiny zero-dependency CLI that builds a correction prompt and pipes it into whatever is on your machine — claude, codex, gjc, gemini, ollama, any OpenAI-compatible API, or any shell command that reads a prompt and prints an answer. No accounts, no API keys (unless you want one), no vendor lock-in.

And the part that makes it stick: fixen install hooks your AI chat CLIs so every normal chat reply ends with a correction of what you typed. You learn while you work, for free, without opening a single flashcard app.

Install

npm install -g fixen-cli    # installs the `fixen` command

Requires Node.js ≥ 18 and at least one backend — if you can run claude, codex, gjc, gemini, or ollama in a terminal, you're done.

Platform: macOS and Linux are fully supported. On Windows, the ollama and api backends work natively, but the AI-CLI backends and -c/--command need a POSIX shell — run fixen under WSL.

Updating

fixen update            # upgrade the package, then rewrite the rule with the new version
fixen update --check    # just compare versions (exit 1 if outdated) — safe for scripts

npm install -g fixen-cli@latest only replaces the binary: RULE.md and the one-liners in your CLIs keep the wording of whatever version wrote them. fixen update does both halves — it detects your package manager from the install path (npm, pnpm, yarn, bun; override with FIXEN_UPDATE_CMD), upgrades, then re-runs install with the new binary so the rule matches the new code. A git/npm link checkout is never overwritten: it reports where the copy lives and refreshes only the rule.

Usage

fixen "your english sentence"     # one-shot
echo "your sentence" | fixen      # stdin / pipes
fixen                             # interactive mode (type lines, Ctrl+D to quit)
fixen -e "sentence"               # also explain what was fixed
fixen -e -l Korean "sentence"     # explanations in Korean
fixen -t Japanese "日本語の文"      # correct any language, not just English

English is just the default. -t/--target (or FIXEN_TARGET, or "target" in the config) switches the language being corrected — fixen -t French -e -l Korean "..." corrects French and explains the fixes in Korean.

Chat mode: corrections inside your AI CLI

The killer feature. fixen install writes the full rule once to ~/.config/fixen/RULE.md, detects which AI CLIs are installed, and adds exactly one marked line to each one's global instructions — a compact version of the rule plus a pointer to the rule file. From then on, your normal chats end like this:

$ fixen install
rule  ~/.config/fixen/RULE.md
ok    claude: ~/.claude/CLAUDE.md  (one line added)
ok    codex:  ~/.codex/AGENTS.md   (one line added)
ok    gjc:    ~/.gjc/agent/AGENTS.md (one line added)

$ gjc -p "hey what is capital of france? my dream is go to paris someday"
The capital of France is Paris. ...

> **fixen** · My dream is **to** go to Paris someday.
> ↳ '가다'는 to부정사로 — go → to go

Ask about Kubernetes, get better English on the side. Every message you type is a free micro-lesson.

Out of the box it knows the global instruction locations of claude, codex, gjc, gemini, qwen, opencode, windsurf, goose, crush, and cline — only the ones actually present are touched. Using something else? Point at its instruction file directly (tracked in a manifest, so uninstall cleans it too):

fixen install -f ~/.someai/INSTRUCTIONS.md

Details that keep it polite:

• Only fires when your own writing has mistakes — correct sentences, pasted code, logs, and quotes are left alone.
• fixen install -t Japanese watches Japanese instead; -e -l Korean adds one-line reasons in Korean.
• Your existing CLAUDE.md/AGENTS.md content is untouched: one marker-wrapped line in, one line out. For Claude Code the line uses the native @~/.config/fixen/RULE.md import, so the full rule is inlined automatically.
• fixen uninstall removes every trace (pointer lines and the rule file); fixen status shows where it's active. Re-running install is idempotent and upgrades old-style installs in place, and fixen update does that for you after every version bump.
• install regenerates the rule from the flags and config it sees, so a bare fixen install after fixen install -t Japanese -e falls back to defaults — keep "target", "lang", and "explain" in config.json instead of retyping flags.
• Applies to new chat sessions.

Backends

Auto-detected in this order: claude → codex → gjc → gemini → ollama → api (if an API key is set). Pick one explicitly with -b:

| Backend | Uses | | -------- | ------------------------------------------- | | claude | claude -p (Claude Code) | | codex | codex exec (OpenAI Codex CLI) | | gjc | gjc -p (Gajae Code) | | gemini | gemini -p (Gemini CLI) | | ollama | ollama run <model> — local, offline | | api | any OpenAI-compatible /chat/completions |

Custom command

Anything that reads a prompt and prints an answer works:

fixen -c 'my-llm --quiet {prompt}' "its a beautiful day"   # {prompt} → the prompt, safely quoted
fixen -c 'my-llm --stdin'          "its a beautiful day"   # no {prompt} → prompt piped to stdin

API backend

export FIXEN_API_KEY=sk-...
export FIXEN_API_URL=https://api.openai.com/v1   # or any OpenAI-compatible server
export FIXEN_MODEL=gpt-4o-mini
fixen -b api "sentence"

Configuration

Defaults live in ~/.config/fixen/config.json:

{ "backend": "claude", "model": null, "command": null, "lang": "Korean", "target": "English", "explain": true }

Environment variables FIXEN_BACKEND, FIXEN_BACKEND_CMD, FIXEN_TARGET, FIXEN_LANG, FIXEN_EXPLAIN, FIXEN_MODEL, FIXEN_API_URL, FIXEN_API_KEY override the config; CLI flags override everything (--no-explain turns off a config-enabled explain for one run). A failed backend attempt is retried once; tune with FIXEN_RETRIES (0 disables retries).

Why fixen

• Zero dependencies. One file, ~29 KB unpacked. npm install finishes before you blink.
• Bring your own model. Your existing CLI subscription or a local ollama model — fixen doesn't care and never sees your text itself.
• Any language. English by default; -t corrects Japanese, French, German, anything.
• Reversible. fixen uninstall puts every touched file back exactly as it was.

License

MIT