Every AI tool in this list is installed on my own Chrome profile right now. I use them daily across writing, research and email workflows, so everything below comes from actual use — not from the Chrome Web Store copy. Prices are the ones the extensions were charging on April 2026, quota numbers are the ones I ran into myself.
The landscape shifted in early 2026 when Monica and Merlin both started offering GPT-4o, Claude 3.5 Sonnet and Gemini 1.5 Pro from the same sidebar. That killed most of the single-provider extensions (like the old ChatGPT-only ones). If you are going to install one AI extension, it should be a model-switcher. The list below is ordered that way.
What it does: Sidebar that runs GPT-4o, Claude 3.5 Sonnet, Gemini 1.5 Pro, and Llama 3.1 405B from one interface. Includes summarise-this-page, translate, chat-with-PDF, rewrite selected text, and reply-to-email macros.
Free tier: 40 GPT-4o messages per day, unlimited GPT-3.5, 30 summaries. Enough for moderate daily use.
Paid: $9.99/mo (billed yearly) unlocks unlimited GPT-4o, Claude 3.5 Sonnet, DALL-E 3 and Midjourney. Annual plan is the only one that makes sense — monthly is $16.90.
Runs on: Chrome, Edge, Firefox, Safari. The Firefox build lags about two weeks behind Chrome on new features.
Watch out for: The default install adds a "Monica" button to every Google search results page. You can disable it in settings but most users never find that toggle.
What it does: Very similar feature set to Monica (sidebar + page summarise + email reply), but Merlin's daily quota is higher on free tier and their UI clusters queries by task rather than by conversation.
Free tier: 102 queries per day, split across any model (GPT-4o, Claude 3.5, Gemini). If you summarise articles frequently, Merlin stretches further than Monica on free.
Paid: $19/mo for unlimited queries + image generation. Pricier than Monica's annual but no annual lock-in.
Runs on: Chrome and Edge only. No Firefox build as of April 2026.
Watch out for: Aggressive page reading — Merlin can pull content from any tab in the background to build "context". Review the permission scope before installing if that matters to you.
What it does: A cleaner, lighter sidebar than Monica or Merlin. Built-in "explain", "translate", "grammar fix" and quick ChatGPT-style chat. Less feature bloat, faster to open.
Free tier: 10 GPT-4o messages per day, unlimited GPT-3.5. Tighter than Monica, but if you only use AI for occasional grammar and explanations, the 10/day is enough.
Paid: $10/mo for unlimited GPT-4o and Claude. Cheapest paid tier on the list.
Runs on: Chrome, Edge, Firefox, Safari.
Best for: users who want AI-on-demand but don't want the sidebar taking over their browsing experience.
What it does: Everything the other sidebars do, plus scheduled jobs that scrape a URL on a schedule and send you a summary by email or Telegram. You can build "price drop" monitors, "new job alerts", or custom RSS-style digests.
Free tier: Unlimited basic chat on their Harpa model, 10 automation runs per day.
Paid: $9/mo for 200 automation runs per day and access to GPT-4o. Semi-Pro is $19/mo with 1,000 runs.
Runs on: Chrome only.
Watch out for: Background automation runs can slow Chrome noticeably on machines with <16GB RAM. Disable jobs you are not using.
What it does: Grammar, spelling and tone checks on any text input field in any site (Gmail, Docs, LinkedIn, Notion, Slack). Added GPT-powered "rewrite" and "tone adjust" in 2024; in 2026 those features are mature and reliable.
Free tier: Grammar, spelling, basic suggestions. Zero AI rewrites on free.
Paid: Premium $12/mo for rewrites, tone adjuster, plagiarism check and fuller vocabulary suggestions. Business tiers start at $15/user/mo.
Runs on: Chrome, Edge, Firefox, Safari, and as a desktop app.
Best for: Anyone who writes professional emails, reports or content and wants a safety net. The 2026 AI rewrites are the differentiator over pure grammar extensions.
What it does: Inline autocomplete in Gmail and Google Docs. Press Tab to accept a suggested continuation of whatever you are typing. Not a sidebar — works like GitHub Copilot for prose.
Free tier: 1,500 words per month. Enough for ~10-20 emails.
Paid: $9.99/mo for unlimited.
Runs on: Chrome, Edge.
Best for: people who answer a lot of repetitive emails. The "rephrase this" and "draft a reply" buttons in Gmail are where Compose earns its keep.
What it does: Replaces the "new tab" search bar with a Perplexity query — you get an AI summary with cited sources instead of 10 blue links. Also adds a "summarise page" button.
Free tier: Unlimited queries on their default model. 5 Pro searches per day (uses GPT-4o or Claude 3.5 Sonnet).
Paid: Pro is $20/mo and unlocks 300 Pro searches per day, plus file uploads.
Runs on: Chrome, Edge, Firefox, Safari.
Best for: research tasks. If you search "why does X happen" frequently, Perplexity's cited answers are faster than Google + reading through SEO content.
What it does: Sits on top of any article you read and highlights terms, people, concepts. Hover any highlighted word and Wiseone fetches an AI explanation in the sidebar. Great for dense articles (academic, financial, medical).
Free tier: Everything. No paid tier exists. Funded by YC seed rounds.
Runs on: Chrome, Edge, Firefox.
Best for: reading long-form content where you keep hitting unfamiliar terms. The "ask a question about this article" feature is genuinely useful and you don't pay for it.
| Extension | Free tier | Paid (cheapest) | Firefox? |
|---|---|---|---|
| Monica AI | 40 GPT-4o/day | $9.99/mo yearly | ✓ |
| Merlin | 102 queries/day | $19/mo | ✗ |
| Sider | 10 GPT-4o/day | $10/mo | ✓ |
| Harpa AI | 10 automations/day | $9/mo | ✗ |
| Grammarly | Grammar only | $12/mo | ✓ |
| Compose AI | 1,500 words/mo | $9.99/mo | ✗ |
| Perplexity | Unlimited basic | $20/mo | ✓ |
| Wiseone | Everything | — (free) | ✓ |
Every extension on this list asks for "read and change all your data on the websites you visit" during install. That permission scope is necessary for sidebars to inject themselves into any tab — it's not inherently malicious, but it means the extension has technical capability to read anything on your screen.
What matters more is what the extension does with that capability. From the privacy disclosures on each Chrome Web Store listing as of April 2026:
If privacy is a hard constraint, install from narrowest-scope to widest: Wiseone → Sider → Monica → Compose → Grammarly → Perplexity → Merlin → Harpa.
Three extensions covers 90% of what browser AI can do without overlapping features:
Total cost: $9.99/mo (Monica yearly) + $12/mo (Grammarly) = $21.99/month for what amounts to a full AI productivity layer across your browser.
Skip Harpa unless you genuinely need scheduled web automations — most people don't. Skip Merlin if you already have Monica. Skip Compose if Monica's rewrite handles your email flow (it usually does).
Our Best AI Writing Tools roundup goes deeper on Grammarly alternatives and writing-specific extensions.
Read the writing tools guideGrammarly, Monica AI, Sider and Wiseone all have official Firefox add-ons. Merlin and Harpa AI are Chrome-only as of April 2026. Edge and Brave install Chrome extensions natively so they get the full list.
Most require "read and change all your data on the websites you visit" permission to function. That does not automatically mean they log everything — Monica and Sider state they only send text you explicitly select or prompt. Harpa and Merlin are more aggressive: they can read page content in the background. Always review the Chrome Web Store privacy disclosure tab before installing.
For switching between models (GPT-4o, Claude 3.5 Sonnet, Gemini 1.5 Pro) from one sidebar, Monica is better. ChatGPT's official extension only runs on OpenAI models. If you already pay for ChatGPT Plus and don't need other providers, the official one is simpler and has no third-party data layer.
Wiseone is 100% free with no quota. Monica's free tier gives 40 GPT-4o messages/day, which is enough for moderate use. Merlin free tier is 102 queries/day across multiple models. Sider free is 10 messages/day on GPT-4o — tighter.