Niftty 🐚

A nifty code syntax highlighter for the terminal, powered by Shiki.

Niftty is particularly good at:

• Rendering diffs, including:
  • Collapsing common regions
  • Highlighting words/characters changed in modified blocks
• Streaming code rewrites generated by an LLM

Known limitations:

• Requires a modern, xterm-256color-friendly shell.

Installation

Grab it with your favorite package manager:

npm install niftty

Usage

import { niftty } from "niftty";

process.stdout.write(
  await niftty({
    code: "let foo = 123;",
    diffWith: "let foo = 456;",         // remove to not render a diff
    lang: "tsx",                        // or any shiki language
    theme: "catppuccin-frappe",         // or any shiki-friendly theme
    lineNumbers: "both",                // remove to hide line numbers
    // collapseUnchanged: true          // to collapse common blocks
    // streaming: true                  // if you're streamin' from an LLM
  })
);

API

niftty(options: Options): Promise<string>

Renders a code snippet using shiki, returning an ANSI-encoded string.

| Parameter | Type | Description | |-----------|------|-------------| | code | string | The code to render | | theme | shiki.ThemeRegistration \| shiki.BundledTheme | Named theme or VSCode-compatible theme object | | diffWith? | string | Code to diff against for showing additions/removals | | lang? | shiki.BundledLanguage \| shiki.SpecialLanguage | Language for syntax highlighting (auto-detected from filePath if not provided) | | filePath? | string | File path to help with language detection when lang is not specified | | collapseUnchanged? | boolean \| Partial<CollapseConfig> | Whether to collapse unchanged lines in diffs | | streaming? | boolean \| number | Enable streaming mode for LLM code generation. Number customizes window size | | highlighter? | shiki.Highlighter | Reuse a shiki highlighter instance for better performance | | lineNumbers? | boolean \| "both" | Show line numbers. Use "both" for old and new line numbers in diffs |

Streaming

If you're building a coding agent and streaming code from an LLM, and want to show that, turn on streaming mode, and feed in the original code (diffWith and the partial currently-emitted code. Niftty will render an on-the-fly diff.

niftty({
  // ...
  streaming: true  // or a number (e.g. 10) for a window of that size
  highlighter: myHighlighter  // re-use a shiki instance
  // ...
});

That looks like this:

Themes

Any VSCode- or shiki-compatible theme should work on modern shells.

More

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