__    _             _                                ___                          _
   / /_  (_)___  ____  (_)____      ________  ____ _____/ (_)___  ____ _  ____ _   __(_)___ ___
  / __ \/ / __ \/ __ \/ / ___/_____/ ___/ _ \/ __ `/ __  / / __ \/ __ `/ / __ \ | / / / __ `__ \
 / /_/ / / /_/ / / / / / /__/_____/ /  /  __/ /_/ / /_/ / / / / / /_/ / / / / / |/ / / / / / / /
/_.___/_/\____/_/ /_/_/\___/     /_/   \___/\__,_/\__,_/_/_/ /_/\__, (_)_/ /_/|___/_/_/ /_/ /_/
                                                               /____/

Toggleable and customizable bionic reading for Neovim using syllable-based highlighting and TreeSitter.

Font: VictorMono | Config: AstroNvim with my setup

What is bionic reading?

Bionic reading is a technique that highlights the beginning of each word to guide your eyes through text faster. Your brain fills in the rest of each word automatically, improving reading speed and comprehension.

bionic-reading.nvim uses a custom syllable algorithm to determine how much of each word to highlight (up to 60% of the word length), giving more natural results than a fixed character count. Combined with TreeSitter, you get fine-grained control over what gets highlighted — only comments, only strings, or the entire file.

Features

• No dependencies
• Syllable-based highlighting with a custom algorithm
• TreeSitter integration — highlight specific node types per filetype
• Toggleable auto-highlighting on file open
• Toggleable insert-mode updates
• Customizable highlight style (bold, italic, underline, color, etc.)
• Persistent highlighting across colorscheme changes
• Prompts before highlighting unlisted filetypes (can be disabled)
• Optional nvim-notify support

Requirements

The default style uses bold text. Make sure your terminal and font support bold rendering, or the highlighting will be invisible.

Terminal-specific settings

iTerm2: Settings → Profiles → Text → Text Rendering → enable "Draw bold text in bold font"

Terminal.app: Settings → Profiles → Text → enable "Use bold fonts"

Installation

Install with your preferred package manager. You must call setup() for the plugin to work.

lazy.nvim

{
  'FluxxField/bionic-reading.nvim',
  config = function()
    require('bionic-reading').setup()
  end,
}

mini.deps

MiniDeps.add('FluxxField/bionic-reading.nvim')
require('bionic-reading').setup()

Configuration

All options shown below are the defaults. You only need to include values you want to change.

require('bionic-reading').setup({
  -- Automatically highlight matching filetypes when a buffer is opened
  auto_highlight = true,

  -- Filetypes to highlight and which TreeSitter node types to target.
  -- Use "any" to highlight everything, or a list of node type names.
  file_types = {
    ["text"] = "any",
    ["lua"] = {
      "comment",
    },
  },

  -- Highlight style passed to nvim_set_hl() (see :help nvim_set_hl)
  hl_group_value = {
    bold = true,
  },

  -- Prompt before highlighting a filetype not listed above
  prompt_user = true,

  -- Use TreeSitter to scope highlighting (falls back to regex if unavailable)
  treesitter = true,

  -- Update highlights as you type in insert mode
  update_in_insert_mode = true,
})

TreeSitter

TreeSitter lets you target specific node types per filetype. For example, the default config only highlights comment nodes in Lua files, leaving code untouched.

You can use any valid TreeSitter node type name for your language. To find available node types, use :InspectTree on a file.

You need the language parser installed for TreeSitter to work:

:TSInstall lua

If TreeSitter is enabled but no parser is available for the current buffer, the plugin falls back to regex-based highlighting automatically.

Syllable Algorithm

Most bionic reading tools take a shortcut: bold the first N characters of every word (typically half). This produces awkward results — **str**ing splits mid-syllable, **thro**ugh bolds into the vowel cluster, and short words like **t**he barely get touched.

bionic-reading.nvim uses a custom syllable detection algorithm instead. It analyzes the actual structure of each word — onset, nucleus, and coda — to find where the first syllable ends, then highlights up to that point.

How it works

1. Short words (1-4 characters) use a simple half-length rule since syllable boundaries aren't meaningful at that scale.
2. Vowel cluster detection — The algorithm recognizes 15 common vowel pairs (ea, ou, ai, oo, etc.) and treats them as a single nucleus. This keeps clusters like the eau in "beautiful" or the ou in "through" from being split.
3. Consonant/vowel classification — Each character is classified to locate the first nucleus. The letter y gets special handling: it's a consonant at the start of a word ("yellow") but a vowel when it doesn't precede another vowel ("system").
4. Coda exceptions — Certain consonant pairs (gh, nd, ld, st) are included with the syllable when they follow the nucleus, matching natural pronunciation ("string", not "string").
5. 60% cap — As a safety net, highlighting never exceeds 60% of the word length, preventing over-bolding on edge cases.

Comparison

Word	Fixed half	Syllable algorithm
string	string	string
through	through	through
beautiful	beautiful	beautiful
comment	comment	comment
reading	reading	reading
yield	yield	yield

The result is highlighting that follows how you actually read and pronounce words, not an arbitrary character count.

Commands

" Toggle bionic reading for the current buffer.
" Prompts if the filetype is not in your config.
:BRToggle

" Toggle insert-mode highlight updates
:BRToggleUpdateInsertMode

" Toggle auto-highlighting on file open
:BRToggleAutoHighlight

Keymaps

No keymaps are set by default. Example:

vim.keymap.set('n', '<leader>br', '<cmd>BRToggle<cr>', { desc = 'Toggle bionic reading' })

API

The plugin exposes two functions for programmatic use:

local br = require('bionic-reading')

-- Highlight a range (0-indexed, end-exclusive). Omit args for full buffer.
br.highlight(bufnr, line_start, line_end)

-- Clear all bionic reading highlights in a buffer
br.clear(bufnr)

Why syllable highlighting?

• Word recognition — Highlighting the first syllable lets your eyes lock onto the core of each word quickly, especially with long or unfamiliar terms.
• Mental chunking — Breaking words into syllable-sized units helps your brain process and retain information more efficiently.
• Code readability — Distinguishing similar variable names, function names, and identifiers becomes easier when their opening syllables are visually distinct.
• Pattern identification — Repeated syllable patterns become visible at a glance, useful for proofreading and spotting repetition.