LexiLint MCP — Spell Checker for Claude and Cursor

What is the Model Context Protocol (MCP)?

The Model Context Protocol (MCP) is an open standard that allows AI assistants to connect to external tools and data sources. Think of it as a universal plugin system for AI.

Instead of the AI being limited to what it knows, MCP lets it:

Read files from your filesystem
Access databases and APIs
Run specialized tools (like spell checkers!)
Connect to any service you authorize

LexiLint MCP provides three tools to AI assistants:

spell_check — Check text for spelling errors (100% offline, free)
grammar_check — Check grammar with AI (BYOK, your API key)
check_text — Combined spell + grammar checking

Use a Local Dictionary for Spell Checking

LexiLint MCP checks spelling with a local dictionary, so the check itself makes no AI provider call. Your assistant still uses a few tokens to send the text and read the result.

Ask a model directly

The text becomes model input
The response becomes model output
Latency and cost depend on the client, model, plan, and text length

Use LexiLint MCP spell_check

Text is checked with a local dictionary
No AI provider call for the check itself
The operation can run without an internet connection

Optional grammar checking still uses the AI provider configured by the user.

Why Use LexiLint MCP?

Check Text on Demand

Give a compatible MCP client a local spell-check tool for prompts, documentation, comments, and other text.

Keep Spell Checking Local

The spell-check operation uses local dictionaries and does not need model tokens or an internet connection.

Support Multiple Languages

The free tier includes US and UK English variants. Premium adds Spanish, French, German, Polish, Russian, and Turkish.

Add Optional BYOK Grammar

Grammar checking uses the API key and provider configured by the user. Provider terms, availability, and charges apply.

Installation

Claude Desktop (Recommended)

Claude Desktop is Anthropic's official desktop app for Claude AI. It has built-in MCP support.

Open your Claude Desktop config file:
- macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
- Windows: %APPDATA%\Claude\claude_desktop_config.json
Add LexiLint to the mcpServers section:
```
{
  "mcpServers": {
    "lexilint": {
      "command": "npx",
      "args": ["-y", "lexilint-mcp"],
      "env": {
        "GEMINI_API_KEY": "your-gemini-api-key"
      }
    }
  }
}
```
Spell checking needs no key. The env block is only for grammar: use GEMINI_API_KEY (free for English), or OPENAI_API_KEY or ANTHROPIC_API_KEY with Premium. Keeping the key here keeps it out of your chats.
Restart Claude Desktop

Quit Claude completely (⌘Q on Mac) and reopen it.
Test it!

In Claude Desktop, type: "Check this text for spelling: Thiss is a tesst"

Claude will use LexiLint's spell_check tool and report the errors.

Other MCP Clients

LexiLint MCP runs as a local (stdio) server, so it works with clients that start local MCP servers:

Cursor: add the same command, args and env in its MCP settings.

OpenAI Codex (the CLI, the IDE extension and the ChatGPT desktop app): add it to ~/.codex/config.toml:

[mcp_servers.lexilint]
command = "npx"
args = ["-y", "lexilint-mcp"]
env = { GEMINI_API_KEY = "your-gemini-api-key" }

Other clients: start npx -y lexilint-mcp and connect over stdio.

ChatGPT chat connects only to remote MCP servers, so it cannot run LexiLint MCP.

Usage Examples

Spell Check (Free, Offline)

Ask your AI assistant:

"Check this text for spelling errors: Thiss is a tesst with errrors"

The AI will use LexiLint's spell_check tool and return:

Found 3 spelling errors:

• "Thiss" (offset 0) → suggestions: This, Hiss, Thins
• "tesst" (offset 11) → suggestions: test, tests, Tess, Tessa
• "errrors" (offset 22) → suggestions: errors

Grammar Check (BYOK)

Add your provider key to the env block of your MCP config (see Installation). Then ask:

"Check this for grammar: This are incorrect grammar"

The AI will use LexiLint's grammar_check tool with your API key and return grammar suggestions. Each call checks up to 2,000 characters; longer text is cut at a sentence or word, and the result says how much was checked.

Combined Checking

"Proofread this entire paragraph for both spelling and grammar errors"

The AI can use the check_text tool to run both checks at once.

Free vs Premium

Feature	Free	Premium
Spell check (en-US, en-GB)	✓ Offline, unlimited	✓
Grammar check with Gemini	✓ BYOK — free key at aistudio.google.com	✓
Spell check in other languages (`check_text`)	✗	✓ es, fr, de, ru, pl, tr
Multi-language grammar	✗	✓
OpenAI grammar	✗	✓ BYOK
Anthropic Claude grammar	✗	✓ BYOK
Custom grammar models (`model`)	✗	✓

Premium: $2.99/month with a 7-day free trial, or $29.99 lifetime. No refunds.
Pass your licence key as license_key in grammar_check or check_text.
Get Premium

Frequently Asked Questions

What is the Model Context Protocol (MCP)?

Model Context Protocol (MCP) is an open standard that allows AI assistants to connect to external tools and data sources. LexiLint's MCP server provides spell and grammar checking to Claude Desktop, Cursor, OpenAI Codex and other MCP clients that run local servers.

How do I install LexiLint MCP in Claude Desktop?

Add LexiLint to your claude_desktop_config.json file: {"mcpServers": {"lexilint": {"command": "npx", "args": ["-y", "lexilint-mcp"], "env": {"GEMINI_API_KEY": "your-gemini-api-key"}}}}. The env block is only needed for grammar. The config file is located at ~/Library/Application Support/Claude/claude_desktop_config.json on macOS or %APPDATA%\Claude\claude_desktop_config.json on Windows.

Does LexiLint MCP work offline?

English spell checking works offline and needs no API key. Grammar checking needs an internet connection and sends the text directly to the provider configured with your API key. Premium languages need an internet connection to check your licence key.

Which clients can use LexiLint MCP?

Clients that run local (stdio) MCP servers, including Claude Desktop, Cursor and OpenAI Codex (the CLI, the IDE extension and the ChatGPT desktop app). ChatGPT chat itself connects only to remote MCP servers, so it cannot run LexiLint MCP. Client capabilities change, so check your client's current MCP documentation.

Is LexiLint MCP free?

The npm package, English spell checking and Gemini grammar for English (with your own Gemini key) are free. Premium ($2.99/month with a 7-day free trial, or $29.99 lifetime) adds six languages, OpenAI and Anthropic, and custom grammar models. Provider charges apply separately.

Which languages are available?

The free tier includes US and UK English. Premium adds Spanish, French, German, Polish, Russian and Turkish. Use them through check_text or grammar_check with your licence key in license_key.

Ready to Add Spell Checking to Your AI Workflow?

Install LexiLint MCP with one config entry. Works with Claude Desktop, Cursor, OpenAI Codex and other MCP clients that run local servers.

Install Now Or Get the Chrome Extension

Local spell checking • BYOK grammar • Free to install (proprietary licence)

LexiLint MCP — Spell & Grammar Checker for Claude Desktop & AI Assistants

What is the Model Context Protocol (MCP)?

Use a Local Dictionary for Spell Checking

Ask a model directly

Use LexiLint MCP spell_check

Why Use LexiLint MCP?

Check Text on Demand

Keep Spell Checking Local

Support Multiple Languages

Add Optional BYOK Grammar

Installation

Claude Desktop (Recommended)

Other MCP Clients

Usage Examples

Spell Check (Free, Offline)

Grammar Check (BYOK)

Combined Checking

Free vs Premium

Frequently Asked Questions

What is the Model Context Protocol (MCP)?

How do I install LexiLint MCP in Claude Desktop?

Does LexiLint MCP work offline?

Which clients can use LexiLint MCP?

Is LexiLint MCP free?

Which languages are available?

Ready to Add Spell Checking to Your AI Workflow?