Shadowtype: On-Device AI Autocomplete for macOS

My notes

Summary

Shadowtype is a free, open-source macOS app that runs a local LLM on Apple Silicon to show inline “ghost text” predictions in any text field, replacing the need for cloud-based AI writing subscriptions. All inference happens on-device via llama.cpp and Metal, so there is no account, no network call for completions, and it keeps working with Wi-Fi off.

Key Insight

• Positions itself directly against subscription AI writing tools by lifetime cost: Grammarly Premium runs $360 in year one and $1,800 over five years, and a comparable cloud rewriting tool runs $240 and $1,200. Shadowtype is a one-time download with all features unlocked forever.
• Works system-wide at the OS caret level (Mail, Slack, Notes, code editors, browser fields) rather than as a separate app window or copy-paste workflow, the differentiator most local-AI writing tools miss.
• Interaction model: Tab accepts the next predicted word, Option-Tab accepts the whole line, and Option-Cmd-K on selected text triggers an inline rewrite (formal, casual, shorten, fix grammar, summarize) that previews before committing.
• Ships a catalog of swappable GGUF models (Qwen3 Base for fill-in-the-middle continuation, Gemma 3, and MoE variants) and supports bring-your-own-GGUF, so the completion quality and speed tradeoff is user-tunable per machine.
• Exposes an OpenAI-compatible HTTP endpoint at 127.0.0.1 (/v1/chat/completions) plus a built-in MCP server, meaning it can double as a free local inference backend for scripts, editor plugins, or MCP clients, not just as a typing tool.
• Offers per-app and per-domain instruction overrides (casual tone in Slack, formal in Mail) and an on-device, encrypted, wipeable style profile that biases completions toward the user’s own phrasing over time.
• The only outbound network traffic, ever, is an optional update check and the one-time model download. There is no telemetry and no churn email, because there is no account to churn from.