You’ve read three Monica vs Sider comparisons and still don’t know which to install. Most skip HARPA AI, and the rest hand four-out-of-five stars to everyone.
So I ran the same workload through all three for 30 days: email replies, research, PDF summaries, and one weekly automation task. One changed how I browse. One added friction. One has been parked in my toolbar unused since week two. Here’s which is which.
What Each One Actually Is (Skipping the Marketing Copy)
The Chrome store treats them as the same product. Spend ten minutes and they feel identical. Spend a week and they diverge.
Monica is a command-bar assistant. Highlight text, hit a shortcut, get rewrites or translations inline. 30M+ installs, multi-model (GPT-5.2, Claude 4.5, Gemini 3 Pro), the most polished UX.
Sider is a research-oriented sidebar. Opens next to any page for summarization, side-by-side model comparison, and PDF Q&A. ~2M users. Built for reading and querying.
HARPA AI is a browser agent, not a chat tool. 100+ commands for automation: price monitoring, change tracking, form filling, scraping. Multi-model, plus a lifetime plan the others don’t offer.
Monica is for what you write. Sider is for what you read. HARPA is for what you automate. Picking the wrong one is the difference between a tool you live in and one you uninstall by Friday.
The 30-Day Test: Same Tasks, Three Tools
Five workloads, daily, for 30 days. Email replies in Gmail. Research queries with citation gathering. PDF summarization (10–60 page reports). Page-level Q&A on docs. One weekly automation task — tracking price changes on a vendor page.
I rotated the primary sidebar each week and round-robined per-task assignments, so no tool got only the easy questions. I tracked time-to-result on identical prompts, output quality (kept, rewrote, discarded), and how often I hit a credit wall.
What I didn’t track: synthetic benchmarks or “productivity multipliers.” Those numbers are theater. I cared whether I’d reinstall the tool tomorrow if Chrome wiped my profile.
Three tools. Same work. Very different outcomes.
Where Each One Wins (and Where It Falls Apart)
| Tool | Owns | Falls apart on | Verdict |
|---|---|---|---|
| Monica | Inline writing, rewrites | Heavy “advanced credit” use | Best free tier, throttled at top |
| Sider | Research, PDFs, multi-model | Casual or intermittent use | Best research, painful price |
| HARPA AI | Automation, monitoring | Anything that needs polish | Power tool, not a daily driver |
The differences below aren’t rounding errors.
Monica: Owns Writing, Loses to Its Own Credit System
Monica’s command bar is the fastest path from “highlight a sentence” to “rewritten in three styles.” Translations and tone shifts felt native to the page — Gmail, Notion, anywhere. The free tier covered casual writing for the first week.
Then advanced credits ran out. Heavy use burns through them in days even on Pro at $9.90/month, and the model silently drops to a weaker one. I caught it because two consecutive rewrites came back nearly identical to the original. That’s GPT-3.5-tier behavior in 2026.
Verdict: install if writing is your daily AI use case and you accept that “unlimited” has fine print.
Sider: Owns Research, Loses on Price and Expiring Credits
Sider’s PDF summarization was consistently fastest on long documents. Its side-by-side model comparison caught factual errors I’d otherwise have shipped — querying GPT, Claude, and Gemini on the same prompt is a research superpower I didn’t know I needed. If research is your core use case, I compared the full landscape of AI research tools that actually deliver — Perplexity, Elicit, Consensus, and more.
The free tier isn’t enough for real work. Pro is ~$20/month or ~$200/year, and credits expire monthly — pure waste on an intermittent load.
Verdict: best in class when research is consistent and heavy. Painful as a casual tool.
HARPA: Owns Automation, Loses on Anything That Needs Polish
Nothing else here can monitor a page for changes, fill forms on a schedule, or pull structured data without leaving the browser — closer to dedicated scraping tools than a chat sidebar. I tracked vendor prices weekly and got alerts that would otherwise have taken a custom script. The lifetime plan ($75–$200 in recent deals) ends the subscription question.
The downsides are real. Writing quality is mediocre. The UI is the “200-item menu” problem. Automations break on auth-gated or heavily JS-rendered pages.
Verdict: a power tool, not a daily driver. Worth the lifetime plan if you have automation work. Skip it if you don’t.
The Credit System Reality Check
The pricing pages don’t tell you what real usage costs.
Monica free covered under-an-hour daily writing. Pro at $9.90/month sounds generous — but the throttle that matters is “advanced credits,” not the headline number. Heavy days exhaust them in a week.
Sider free is a demo, not a product. Pro at ~$20/month or $200/year is the real entry point. Credits expire monthly, so annual billing only makes sense if research is steady.
HARPA free is the most generous for evaluation. The lifetime plan ($75–$200 in recent deals) is the only one without recurring cost.
Heavy-use math: HARPA lifetime plus Monica Pro covers writing and automation for less than Sider Pro alone. Research-heavy? Sider stings. Automation-heavy? HARPA pays back inside a year.
When You Don’t Need Any of These
If most of your AI time already happens at chat.openai.com or claude.ai, a sidebar is friction — you’ve trained yourself on direct prompting, and a sidebar adds a step.
Chrome’s built-in Gemini, Edge Copilot, and browser-native AI in Atlas, Comet, and Dia are eating the easy wins for free. These three earn their slot only if you do something inside other pages — drafting in Gmail, summarizing client docs in-line, or automating recurring web tasks.
If that’s not you, save the install. The right number of AI sidebars is sometimes zero.
The Bottom Line: Which One Stayed Installed
After 30 days, HARPA stayed pinned — the automation work justified it, and the lifetime plan ended the recurring-cost question. Monica earned a permanent spot too: the free tier covers writing and the command bar is faster than alt-tabbing to ChatGPT. Sider got uninstalled on day 31. Its strengths were real, but my research load isn’t steady enough to justify $200 a year of expiring credits.
Per reader: writing-heavy → Monica. Research-heavy and consistent → Sider. Automation → HARPA. Mixed and budget-aware → Monica free plus HARPA lifetime, which is where I landed.
The right tool isn’t the one with the best landing page — it’s the one that matches what you actually do in a browser. Open yours and look at the tabs. That’s your answer.