opencode-ascii

An OpenCode plugin that automatically substitutes unicode characters with ASCII-safe equivalents in AI responses and file edits.

Why?

LLMs love to reach for typographic characters — em-dashes, curly quotes, arrows, emoji — that look great in a browser but cause friction in terminals, code, config files, and plain-text tooling. This plugin intercepts output at two points:

• AI text responses (experimental.text.complete) — rewrites text parts before they are stored.
• File write/edit tool calls (tool.execute.before) — rewrites write, edit, multiedit, and apply_patch tool arguments before execution.

Installation

Add the package to your opencode.json:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": ["opencode-ascii"]
}

OpenCode will install the package automatically via Bun at startup.

Configuration

All four substitution categories are enabled by default. Disable any category by passing options:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": [
    ["opencode-ascii", {
      "punctuation": true,
      "arrows": true,
      "math": true,
      "emojis": false
    }]
  ]
}

| Option | Type | Default | Description | |---------------|---------|---------|----------------------------------------------| | punctuation | boolean | true | Em/en dashes, ellipsis, curly/smart quotes | | arrows | boolean | true | → → ->, ← → <-, ⇒ → =>, etc. | | math | boolean | true | ≠ → !=, ≤ → <=, × → *, etc. | | emojis | boolean | true | Common emoji -> :shortcode: labels |

Substitution reference

Punctuation

| Unicode | Character | ASCII | |---------|-----------|-------| | U+2014 | — | -- | | U+2013 | – | - | | U+2026 | … | ... | | U+201C | " | " | | U+201D | " | " | | U+2018 | ' | ' | | U+2019 | ' | ' | | U+00AB | « | " | | U+00BB | » | " | | U+2022 | • | - |

Arrows

| Unicode | Character | ASCII | |---------|-----------|-------| | U+2192 | → | -> | | U+2190 | ← | <- | | U+2191 | ↑ | ^ | | U+2193 | ↓ | v | | U+21D2 | ⇒ | => | | U+21D0 | ⇐ | <= | | U+21D4 | ⇔ | <=> | | U+2194 | | <-> |

Math operators

| Unicode | Character | ASCII | |---------|-----------|-------| | U+2260 | ≠ | != | | U+2264 | ≤ | <= | | U+2265 | ≥ | >= | | U+00D7 | × | * | | U+00F7 | ÷ | / | | U+00B1 | ± | +/- | | U+2212 | − | - | | U+221E | ∞ | inf | | U+2248 | ≈ | ~= | | U+221A | √ | sqrt |

Emojis

| Unicode | Character | ASCII | |---------|-----------|-------| | U+2713 | ✓ | :white_check_mark: | | U+274C | ❌ | :x: | | U+26A0 | ⚠ | :warning: | | U+2139 | ℹ | :information_source: | | U+2B50 | ⭐ | :star: | | U+1F525 | 🔥 | :fire: | | U+1F680 | 🚀 | :rocket: | | U+1F41B | 🐛 | :bug: | | U+1F4DD | 📝 | :memo: | | U+1F512 | 🔒 | :lock: | | U+1F513 | 🔓 | :unlock: | | U+1F4C1 | 📁 | :file_folder: | | U+1F4C4 | 📄 | :page_facing_up: | | U+1F44D | 👍 | :+1: | | U+1F44E | 👎 | :-1: |

and many more!

See src/substitutions.ts for the full list.

How it works

The plugin uses two hooks:

1. experimental.text.complete — fired by OpenCode after each AI text part finishes streaming. The plugin rewrites output.text in place before it is persisted.

2. tool.execute.before — fired before any tool executes. The plugin rewrites:

   • output.args.content for the write tool
   • output.args.newString for the edit tool (never oldString — it must match existing file content exactly)
   • each output.args.edits[].newString for the multiedit tool
   • output.args.patchText for the apply_patch tool

Substitution uses a single compiled regex built from all active mappings, so there is no O(n) string-replace loop per character.

License

MIT