mdt

A CLI that translates a single markdown file using the opencode SDK as its engine. It reuses your existing opencode authentication and provider configuration, and locks down every available tool so the model can only read the input prompt and produce text output.

Why this exists

• You already have opencode set up with providers and auth — mdt borrows that wiring instead of asking for new API keys.
• Translation is a single-shot text task; the agent harness, filesystem access, and shell tools that opencode normally exposes are unnecessary and risky for this use case.
• mdt runs an in-process opencode server, fetches every tool ID via /experimental/tool/ids, and disables them all on the prompt. The model sees the input markdown and nothing else.

Install

This package is part of the workspace; install once at the repo root:

pnpm install
vp run --filter @totto2727/mdt build

The binary lands at js/app/mdt/dist/bin.mjs.

Usage

mdt <file> --lang <code> [--model <provider/model>] [--force]

| Flag | Alias | Description | Default | | --------- | ----- | ---------------------------------------------- | ------------------------------- | | --lang | -l | Target language code (e.g. ja, en) | required | | --model | -m | Model in provider/model format | opencode-go/deepseek-v4-flash | | --force | -f | Overwrite the output file if it already exists | off |

Output path rules

mdt writes to a sibling file with the language tag inserted before the extension. Compound extensions like .mbt.md are preserved.

| Input | --lang ja output | | ----------------- | ------------------------------------------------ | | hoge.md | hoge.ja.md | | hoge.mbt.md | hoge.ja.mbt.md | | README.draft.md | README.draft.ja.md | | hoge.en.md | hoge.ja.md (existing language tag is replaced) | | hoge.en.mbt.md | hoge.ja.mbt.md |

The known language tags are ja and en. The known compound extensions are .mbt.md. Both lists live in src/lib/path.ts.

Examples

# Translate to Japanese with the default model
mdt docs/intro.md --lang ja

# Translate to English with a specific model
mdt docs/intro.ja.md --lang en --model anthropic/claude-sonnet-4-6

# Overwrite an existing translation
mdt docs/intro.md --lang ja --force

Editor integration

Any editor that can run a shell command on the current buffer can drive mdt. The Zed example below assumes the binary is on PATH.

.zed/tasks.json:

[
  {
    "label": "mdt: translate to ja",
    "command": "mdt $ZED_FILE --lang ja"
  }
]

How it works

1. createOpencode() boots an in-process opencode server that inherits your opencode.json and stored credentials.
2. client.tool.ids() enumerates every built-in and MCP-registered tool.
3. client.session.create() opens a fresh session.
4. client.session.prompt() sends the file contents with tools set to { [id]: false } for every ID, plus a system prompt that constrains the model to emit only the translated markdown.
5. client.session.messages() retrieves the assistant response, and the concatenated text parts are written to the resolved output path.
6. The opencode server is closed when the Effect scope exits.

Limitations

• The default model opencode-go/deepseek-v4-flash must be configured as a provider in your opencode setup. Override with --model if you use a different provider.
• The /experimental/tool/ids endpoint is currently under experimental in the opencode API. The SDK should track any future relocation, but breakage is possible.
• Large markdown files may exceed the model's context window. There is no chunking; one prompt translates the whole file.