ShroomPen
Ivan Balshalapau · Writing · Voice & Language · Productivity
ShroomPen is a free Chrome extension that replies, rewrites, fixes grammar and translates inside any text field, using your own AI provider or a local model.
About ShroomPen
What Is ShroomPen
ShroomPen is an AI writing assistant that lives in the corner of whatever page you are typing on. Open a support ticket, an email draft, a LinkedIn comment or a CRM note, and the extension works on the text already in that field. You pick one of four actions, check the result, then insert or replace.
The difference from most writing extensions is where the intelligence comes from. ShroomPen ships no model of its own and runs no server. You connect OpenRouter, OpenAI, Anthropic, Google Gemini or a custom endpoint, or you point it at Ollama or LM Studio on your own machine. The extension is free, and the only bill is whatever your provider charges.
That design has a tradeoff. Setup takes a few minutes, and you need an API key or a local model before anything works. Once connected, ShroomPen can pull context from the page you are on, text you select, and tabs you deliberately attach, which is enough to answer a message with the order number and delivery date already in it.
Getting Started
- Install the extension from the Chrome Web Store and pin it to the toolbar.
- Open the provider guide, then sign in with OpenRouter or paste a key from OpenAI, Anthropic or Google. For a local setup, enter the address of your Ollama or LM Studio server.
- Click into any text field and open the ShroomPen overlay. Pick Reply, Rewrite, Fix grammar or Translate.
- Switch on the context you want, such as the current page or a specific tab, review the draft, then insert or replace the text.
Product Information
A quick look at ShroomPen's pricing, supported platforms, and performance.
Best for
The users, tasks, and scenarios where this tool fits best.
Users
- Customer support agents
- Founders and sales reps
- Non-native English speakers
- Privacy-conscious professionals
Tasks
- Answering a support ticket with details from another tab
- Rewriting a blunt sentence into a calm one
- Fixing grammar in a cover letter or a visa form
- Translating a chat message without losing tone
Scenarios
- A helpdesk shift with a queue of similar tickets
- Replying to a customer while a call is still running
- Drafting a proposal from three open documents
Key features
Four actions in one overlay
Reply, Rewrite, Fix grammar and Translate all run on whatever sits in the active field. Reply treats your rough note as a brief and writes the full message. Rewrite keeps the meaning and changes the wording. The grammar checker fixes spelling, punctuation and sentence structure, and Translate swaps the language while keeping the register, so you can translate text in browser without opening another tab. One shortcut opens the panel, so you are not hunting through menus for a tool you use ten times a day.
Context from the tabs you pick
A tab picker lists the pages you have open, and ShroomPen reads only the ones you tick. That is how a reply ends up with an invoice number from the billing tab, a delivery date from the courier page and a name from the CRM record. Untick a tab and the draft loses what only that page knew. Page text is capped at 12,000 characters per request, and PDF tabs are parsed in the extension up to 40,000 characters or 80 pages.
Workspaces for standing instructions
A Workspace holds the rules you would otherwise retype: tone of voice, escalation policy, product facts, imported notes in .txt or .md. Turn it on and every request in that window follows it. Workspaces stay in local extension storage, so a support team can share a written brief without handing over an account or a cloud workspace.
Bring your own provider
ShroomPen works as a BYOK AI assistant. Sign in with OpenRouter in one click, or paste a key from OpenAI, Anthropic or Google Gemini. Custom OpenAI-compatible endpoints are supported over HTTPS, and loopback addresses can stay on plain HTTP for Ollama or LM Studio. If you run a local AI model, the extension costs nothing to operate and your text never leaves the machine.
Insert or replace, with a preview
Results appear in a panel before they touch the page. You can read the draft, edit it in the box, then choose Insert to append or Replace to overwrite the selected text. The field keeps its own styling, so a reply looks like something you typed in that tool rather than a pasted block. Nothing is written until you press the button.
Privacy controls you can audit
Password, card, bank and one-time-code fields are skipped by design, and you can disable ShroomPen on any domain. The overlay can show the composed request before it is sent, with the API key hidden. There is no ShroomPen account, no telemetry, and no ShroomPen server between your browser and the provider. Keys sit in Chrome extension storage, which is worth knowing if you share a computer.
Pros and cons
Pros
- No subscription. The extension is free, and you pay only your provider, which can be $0 with OpenRouter free models or a local model.
- Tab and PDF context removes the copy and paste step that makes most AI writers useless for support work.
- Four actions cover the common writing jobs without switching to a separate editor or a chat window.
- The privacy model is unusually clear: no account, no server, no analytics, and a request preview before sending.
- Works on any site with a text field, including helpdesks, CRMs and webmail that block other extensions.
Cons
- There is no built-in model or trial credit, so setup fails for anyone who does not have an API key or a local server.
- Chrome and Chromium desktop only. Firefox, Safari and mobile browsers are not supported, which rules out phone replies.
- API keys are stored in extension storage without extra encryption, so a shared or borrowed laptop is a real risk.
- The 12,000 character page cap and the 40,000 character PDF cap will cut off long contracts and books.
Frequently asked questions
Yes. The Chrome extension costs nothing and has no paid plan. You pay the AI provider you connect, and that bill can be zero if you use OpenRouter's free models or run a local AI model through Ollama or LM Studio.
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