AI writing · checked 2026-10-14Can I vibecode LanguageTool?
YES· one-shottable
LanguageTool is the odd one on this list because its engine is already free: the rule-based checker is open source under LGPL-2.1 and runs as a local server that the official browser add-ons can be pointed at. A one-session build puts a pasted-text editor, a personal dictionary, a command-line checker for Markdown and an optional LLM rewrite button on top of that server, which covers what most people use it for. The paid layer stays behind: 20,000-plus extra premium checks for seven languages, the AI rephrasing inside the add-ons (the local server has no AI rules), and the desktop apps.
$24.90/moprice
$299you'd save a year
one sittingbuild time
—people replaced it
What you need on hand.
DifficultyIntermediate · Some system setup or keys.
TimeAn evening, plus time for the Docker image to download
- Claude Code, Codex or CursorAny of them can run the prompt.
- DockerThe server runs in a container; its default Java heap is small, so raise it for long texts.
- Node.js 22For the checker app and the command-line tool.
- An LLM API key (optional)Only the rewrite buttons use it; grammar checks stay on your machine.
Before you buildLanguageTool Basic checks 2,000 characters at a time and the add-ons are free. If your texts are short, you may not need Premium or a build.
- 1. Install one agent: Claude Code, Codex, Cursor.
- 2. Make an empty folder and open it in the agent.
- 3. Paste the prompt below, press enter, and answer its questions as it builds.
The prompt
Build me a local writing checker to replace LanguageTool Premium. Requirements: - Engine: the open-source LanguageTool server from the community Docker image (erikvl87/languagetool) in a docker-compose.yml, bound to 127.0.0.1:8010. Text goes to that server only. - Node.js 22 + TypeScript: a Fastify app on http://localhost:4950 with a text area. It calls POST /v2/check on the local server and underlines each issue with the rule name, the explanation and the suggestions; clicking a suggestion applies it. - Language dropdown plus auto-detect, a "mother tongue" option for false friends, and a Picky mode toggle; the choices persist in ./data/settings.json. - Long texts: split at paragraph boundaries into chunks under 20,000 characters, merge the results and keep character offsets correct. - Personal dictionary in ./data/dictionary.txt, one word per line, applied to every check; a button on a spelling issue adds the word. A list of rule ids I can switch off. - Rewrite pane: Shorter, Clearer and Formal buttons call an LLM with ANTHROPIC_API_KEY from .env and show a word-level diff before I accept. Without the key the buttons are hidden. - CLI: `check <file.md>` prints issues with line numbers and exits 1 when there are any. - No accounts, no telemetry, local-first. Outbound calls: the local server, and the LLM API only when I press a rewrite button. - Out of scope: browser and Office extensions, mobile apps, a style-guide editor, and the paid premium rule sets (the open-source server doesn't have them). - README: Docker setup, how to point the official browser add-on at http://localhost:8010/v2 in its advanced settings, the memory the server wants, and that n-gram data for confused words is an optional multi-gigabyte download that needs a bigger Java heap.
Opens your agent with the prompt filled in, you press enter. Or copy it and paste it into an empty folder.
Then keep going
Next prompts, same folder.
The first prompt builds the core. Run these one at a time in the same folder to grow it into your own LanguageTool.
Extend the LanguageTool setup in this folder. Requirements: - Add a script that downloads the English n-gram data from languagetool.org/download/ngram-data into ./ngrams/ and unzips it, with a clear warning about the size before it starts. - Mount ./ngrams read-only at /ngrams in docker-compose.yml and set langtool_languageModel=/ngrams. - Set Java_Xms and Java_Xmx from .env, with defaults suited to the data. - Add a startup check in the app that reports whether n-grams are active. - Update the README with disk and memory needs, and an SSD recommendation.
Add a personal style guide to the checker app in this folder. Requirements: - A file ./data/style.yml with entries of the form: avoid a phrase, suggest a replacement, optional note. - Match whole words and phrases, case-insensitively, and report them as issues alongside LanguageTool results, with their own colour and a rule id starting with STYLE_. - A settings page to add, edit and delete entries, and import a plain list. - Tests for overlapping matches and for offsets after earlier replacements. - Update the README.
Extend the check CLI in this folder. Requirements: - `check <dir>` walks .md files, skips code blocks, inline code, front matter and URLs, and reports file:line:column. - A --changed flag checks only files that differ from HEAD. - Provide a ready-to-copy .git/hooks/pre-commit script that runs `check --changed` and blocks the commit on issues, with a one-line way to bypass it. - Update the README.
Add a clipboard mode to the checker in this folder. Requirements: - `check --clipboard` reads the clipboard, runs the check, and opens the result page with the text loaded, using pbpaste and open on macOS or xclip and xdg-open on Linux. - Print the platform commands for binding it to a hotkey (Shortcuts on macOS, a desktop shortcut on Linux). - Never write the clipboard text to disk. - Update the README.
What you lose
- The premium rule sets: 20,000-plus extra checks in seven languages
- AI paraphrasing inside the add-ons; the self-hosted server has no AI rules
- Synonym suggestions, which the local server doesn't support
- The desktop and mobile apps; the Windows app doesn't work with a self-hosted server
Why people still pay
Writers who work in several languages pay for rule sets that linguists keep current, and for add-ons that follow them into browsers, Word and phones without a server to look after. Most of the value is the rules, not the interface around them.
LanguageTool or your own copy?
Over
Your usage
3h ×$/h
LanguageTool, 1 yr$299
Your own copy, 1 yr$68running + build session
You keep$231pays for itself in the first month
Estimate · Local use costs nothing; the rewrite pane costs cents per text on the API. A small VPS only matters if you want the server always on, and n-gram data needs more memory than the cheapest ones have. The build is token usage on your agent plan.
Take your data, then cancel.
1 · Take your data out of LanguageTool
- 1Personal dictionary: open the Editor, go to Settings > Team Dictionary, click Import dictionary, then Download existing dictionary for a CSV. The limit is 1,000 words.
- 2Texts typed through the browser add-on usually aren't saved by LanguageTool; only documents in the online editor are. Copy any you need out of the editor.
- 3We found no export for style-guide rules or add-on settings: write them down before you go.
2 · Cancel LanguageTool
- 1Open your account settings, choose My Account, then Cancel subscription. A confirmation email follows.
- 2The plan runs to the end of the period you've already paid for, and no further charges follow.
- 3Premium carries a 14-day money-back guarantee: ask support within that window.
- 4Deleting the account is separate, and accounts with an active Premium subscription are deleted by support, not in settings.
- Plans renew automatically at the interval you picked, so cancel before the renewal date on a yearly or two-year plan.
- After the paid period you drop to Basic, with a limit of 2,000 characters per text field.
- Export the dictionary while you still have Premium, not after.
- A community report says the add-ons accept a self-hosted server URL in their advanced settings; test that before you cancel.
Checked 2026-10-14 against LanguageTool's docs: 1, 2, 3, 4, 5
The escape hatch
Don't feel like building it? These are already free.
LanguageTool (self-hosted)Open sourceThe checker itself under LGPL-2.1: run the Java server or a community Docker image and point the browser add-ons at it. No AI rules or premium rule sets; n-gram data is a separate multi-gigabyte download.★ 15k · active Oct 2026 · docker to self-host
Web, Linux, macOS, WindowsVisit ↗HarperOpen sourceApache-2.0 offline grammar checker written in Rust that lints in milliseconds, with editor and Obsidian integrations; English only.★ 16k · active Oct 2026 · one-click install
Linux, macOS, WindowsVisit ↗ValeOpen sourceMIT command-line prose linter that turns writing guidelines into checks in editors and CI, offline; closer to a style linter than a grammar checker.★ 6.2k · active Oct 2026 · one-click install
Linux, macOS, WindowsVisit ↗
Web, Linux, macOS, WindowsVisit ↗HarperOpen sourceApache-2.0 offline grammar checker written in Rust that lints in milliseconds, with editor and Obsidian integrations; English only.★ 16k · active Oct 2026 · one-click install
Linux, macOS, WindowsVisit ↗ValeOpen sourceMIT command-line prose linter that turns writing guidelines into checks in editors and CI, offline; closer to a style linter than a grammar checker.★ 6.2k · active Oct 2026 · one-click install
Linux, macOS, WindowsVisit ↗
The numbers
LanguageTool pricing
| Plan | Monthly | Annual, per month | What you get |
|---|---|---|---|
| Basic | $0/user | $0/user | 2,000 characters per text field, 3 AI sentence rephrases a day, Picky Mode limited; the editor, browser add-ons and apps. |
| Premium | $24.90/user | $5.83/user | 150,000 characters per text field, unlimited AI paraphrasing, 20,000-plus extra checks for English, German, French, Spanish, Dutch, Polish and Portuguese, personal style guide and dictionary. |
| Team | — | $5.53/user | Everything in Premium plus user management, a team style guide and a team dictionary; from 2 users. |
| Business | custom | — | A separate offer for companies, described as GDPR-compliant, with its own page. |
- Free tier
- 2,000 characters per text field and 3 AI rephrases a day; Picky Mode is limited.
- Billing
- Premium bills monthly, quarterly, yearly or every two years and renews automatically; Team is billed yearly. 14-day money-back guarantee; pay by card or PayPal.
- Hidden costs
- Prices include VAT and appear in the visitor's currency. A limited-time discount banner was running when checked, so figures move with region and promotion.
- Source
- languagetool.org
Also on the list
Related apps
Basic checks texts of up to 2,000 characters at a time and allows 3 AI rephrases a day.
Yes. An AI coding agent such as Claude Code, Codex or Cursor can build a usable personal version in one session with the prompt on this page, running on your own machine.
About $24.90 a month on the Premium plan, $298.80 a year (checked 2026-10-14).
The premium rule sets: 20,000-plus extra checks in seven languages; AI paraphrasing inside the add-ons; the self-hosted server has no AI rules; Synonym suggestions, which the local server doesn't support; The desktop and mobile apps; the Windows app doesn't work with a self-hosted server. If any of those matter to you, keep paying.
Yes: LanguageTool (self-hosted) (open source), Harper (open source), Vale (open source).