Short version: Slido if the session is questions, Mentimeter if the session is slides — and on the free plans that is the whole answer, because they are metered in opposite places. Slido gives away unlimited Q&A for up to 100 people at one event and meters the polls. Mentimeter gives away every slide type and meters the people, 50 a month across everything you run. Neither free plan lets you hold a question for approval before the room sees it, which is the thing most people find out last.
If that last sentence is your problem, it is free at askone.org — along with every other feature, and with an AI first pass for the sessions you run alone.
AskOne is made by The Product Compass. Slido belongs to Cisco, every other tool here belongs to someone else, and their free-tier figures come from each vendor's own pricing and help pages, read in September 2026.
Last updated: September 21, 2026. Slido and Mentimeter figures are quoted from each vendor's own pricing and community pages on that date; free plans in this category move quietly.
The Two Free Plans, Side by Side
Slido Basic
Unlimited audience Q&A. Questions and upvotes are the part Slido does not meter, and for a talk with twenty minutes of questions at the end it is the only part that matters.
Three polls per event. Slido's own community answer says three, and notes that some regions get five.
One quiz per event, with up to thirty questions inside it.
Up to 100 participants per event. Per event, so the count starts again with the next one.
No moderation. Holding a question until someone approves it, and the moderators who do the holding, are on the paid plans — Slido's own plan comparison is the source. On Basic, whatever the room types is on the screen the moment they type it.
The full breakdown, including what to do about the poll budget, is on the Slido free-plan page.
Mentimeter Free
50 participants per month. Mentimeter's own wording is “the number of people who can respond to your Mentis each month”. It is an account-level pool, not a per-presentation cap, and it resets on the day of the month you signed up rather than on the 1st.
One unlimited session a month. The plan grants “unlimited participants once per month”, so a single big session escapes the pool. Choosing which one is your problem.
Every slide type. Word clouds, scales, open text, quizzes and the rest — this is where Mentimeter is genuinely more generous than anyone.
No export on free. Results stay inside Mentimeter until you pay.
Q&A moderation is two tiers up, on Pro at $24.99 per presenter per month billed yearly. Source: mentimeter.com/plans.
The full breakdown, including what the monthly reset does to a busy week, is on the Mentimeter free-plan page.
Where Each One Stops First
Slido stops at the fourth poll
Three polls and one quiz per event is a small budget for a workshop built out of interaction, and the limit is usually met the evening before. The workaround is Slido's own: create a separate event per presentation, which resets the budget and leaves you juggling join codes.
Mentimeter stops on the 12th of the month
A 60-person all-hands uses the 50-participant allowance on the first Tuesday, and the pool does not come back until your signup date comes round again. It is the only free tier in this category that meters by the calendar rather than by the session, which is why it catches people mid-session rather than during the shopping.
Both stop at the same place on moderation
Neither free plan will hold a question for approval. If the session is a conference Q&A, that is usually fine. If it is an internal all-hands where anonymous questions appear on a screen behind an executive, it is the line item that decides the purchase — and on both tools it is an upgrade: Slido puts it on the paid plans with the moderators, Mentimeter on Pro at $24.99 per presenter per month.
And the upgrade does not buy you the hard part. A moderation queue still needs somebody watching it while the session runs, which the person presenting cannot do. That is the gap under both price lists.
What They Charge When You Outgrow the Free Plan
Slido. Third-party trackers put the cheapest paid tier, Engage, at around $17.50 a month billed annually, with the higher tiers quoted rather than listed. Priced around the event and the licence. Check the pricing page for today's version.
Mentimeter. Basic $11.99 and Pro $24.99 per presenter per month billed yearly, Enterprise quoted. Priced per presenter, which is the number that decides it: forty colleagues who each run two sessions a year is forty invoices, not one.
Per event, per presenter, per organization — this is the comparison that actually moves money. The monthly headline rates are close enough to ignore; what differs is what you are buying one of.
Which One, in Three Questions
Is the session slides, or is it questions?
Mentimeter is a presentation tool with interaction inside the slides. Slido is a Q&A tool with polls beside it. Buying the wrong category is the most common mistake here, and no feature grid warns you about it.
How many people, and how often?
Count the worst case, not the average, and then count the sessions per month. One big session a month fits Mentimeter's free plan exactly once. Several sessions a month is where a monthly pool stops being a free plan and starts being a schedule.
Does anyone need to approve questions before they appear?
If yes, both free plans are out, and the cheapest way to say yes on either of them is $24.99 a month per presenter. It is also worth asking who would do the approving, because on most small teams the honest answer is nobody.
The Third Option, Where Neither Meter Exists
askone.org is live Q&A for talks, webinars, all-hands meetings and cohort sessions. A host opens a room and gets a join code; the audience opens a link or scans a QR code on their phones, asks questions, and upvotes the ones they want answered. The room does the ranking, so the top question is the next question.
The meter is per room, and nothing counts down. This is the part worth reading twice, because it is where the free tiers in this category differ most. Most of them meter a calendar month: the account gets a pool of participants, every session draws from it, and when the pool is empty the next audience is refused until the month turns over. AskOne has no such counter. The cap is per room — a room admits up to 100 people, and you can open a room every day of the month without any of them counting against the next one. There is no monthly total, nothing resets, and nothing runs out.
Live Q&A, ranked by the room. The audience asks and upvotes; the top question is the next question, so the hour goes on what people actually wanted answered.
Polls. Single or multiple choice, revealed when you choose.
Word clouds. One-word answers from the room, drawn live as people type — the opener that gets a quiet room talking before anyone has to raise a hand.
Rating scales. A numbered scale with your own labels at each end, and the average as it moves.
Quizzes. A question with a right answer, held back until you reveal it.
Answers from the host, in writing. Type an answer onto a question and it moves to an Answered tab the whole room can read — including the ones you did not get to out loud.
A projector view for the room. The ranked list, readable at the front of a hall.
Moderation, and the moderators who do it. Hold new questions for a person, or let the AI take the first pass and leave you only the ones it was not sure about — both free on every plan, and switchable mid-session. Moderators handle questions and surveys; they never open or close rooms.
No account for your audience. A link or a QR code on their phones. No app, no extension, no sign-up wall between someone and the question they wanted to ask.
The session does not end with the call. When the room closes the host gets the questions and the survey totals, and can export everything as CSV.
Your agent can read the room. A read-only HTTP API and an MCP server, on every plan: every room, question, vote and written answer. So the follow-up FAQ is one sentence to an assistant that already has the session, rather than an afternoon with a spreadsheet.
Everything above is on the free tier, including the one feature this whole comparison keeps running into: holding a question for approval before the room sees it, and the moderators who do it.
And the first read does not have to be yours. A room is set to one of three things and you can change it mid-session: no moderation, hold every question for a person, or let the AI take the first pass. On that third setting each question is classified before anyone sees it, in about a third of a second — inside the wait the person asking already has — and it is included on every plan, within fair use.
It judges civility, never the subject. What it rejects is abuse, harassment, spam and keyboard-mashing. A question that has nothing to do with your session is not on that list, on purpose: in a room ranked by votes an irrelevant question sinks by itself, while a wrongly rejected one is gone and the person who asked it is told it was not accepted. Being wrong is expensive in one direction only, so what is on topic stays the host's call.
When it is not sure, a person decides. Below the confidence line — and on a timeout, or when the model is unreachable — the question waits in the moderation queue instead of being guessed at. The failure direction is always towards a human, never towards the wall.
Nothing is deleted and you can overrule it. Whatever the AI held back sits in its own list for the host to open and restore.
What leaves the room. In an AI room the question text and the room's name and description go to the model. No participant name, cookie or IP goes with them.
Measured on the release that shipped it: a hundred questions through the live classifier — none of the 55 civil ones rejected, 24 of the 25 abusive or spam ones caught outright and the 25th held for a person, so none of them reached the room. Median 315 ms against a two-and-a-half-second budget. It is re-run on every release, because a model can move underneath wording that did not.
You can open a real room right now, without signing up for anything. AskOne keeps one open to the public — askone.org/r/WQYJ7G. Vote a question up the list, answer the live survey, ask something of your own. It is a room on the running product rather than a video or a guided tour, and it resets itself every few hours, so nothing anyone leaves in it stays.
It is also where the AI first pass stops being a claim. A civil question typed into that room on 21 September 2026 was screened and on the wall immediately — inside the wait the person asking already has, which is the entire argument for letting a machine take the first read.
Free is one open room and up to 100 participants — no credit card, no trial clock. Premium raises that to ten open rooms and 1,000 participants per room, at $20 a month or $10 a month billed annually. Every feature on this page is on both plans, moderation and the AI pass included; what the paid plan buys is capacity, and your own logo in place of the small “Create your own room — free” line a free room shows its audience.
What is not there yet: single sign-on, a Teams or Zoom app, and PowerPoint integration. If your organisation buys software through a security review, that last one is the gap to know about.
When Slido or Mentimeter Is Still the Right Answer
Your company already pays for one of them and the seat costs you nothing personally.
The session really is a presentation, and the interaction belongs inside the slides — that is Mentimeter's home ground and it is better at it than anything else here.
You need a vendor with an account manager to call when something breaks in front of five hundred people.
If none of those is true, the free plan you want is at askone.org.
Questions People Ask
Is Slido or Mentimeter better for Q&A?
Slido, on the free plans: its audience Q&A is unmetered for up to 100 people per event, while Mentimeter's Q&A is one slide type inside a 50-participant monthly pool. Neither free plan moderates questions, so if approval matters the comparison is between two upgrades — or askone.org, where it is free.
Which free plan allows more participants?
Slido, for a single event: 100 people per event, with the count starting again at the next one. Mentimeter's 50 is a monthly pool across everything you run, plus one unlimited session a month. So for one big session a month Mentimeter is larger, and for anything regular Slido is.
Does Mentimeter's free plan include Q&A moderation?
No — it is on Pro, at $24.99 per presenter per month billed yearly. The detail is on the Mentimeter free-plan page.
Can my audience join either one without an account?
Yes. Both let people join with a code or a link, and so does askone.org. It is the single biggest predictor of how many people actually take part, so it is worth checking on anything else you shortlist.
What else should I look at?
The wider shortlist — Vevox, Wooclap, AhaSlides, Pigeonhole Live, Poll Everywhere and the open-source one — is on the alternatives page, with what each one was designed around.
Start free at askone.org: one open room, 100 participants, every feature including moderation and the AI first pass, no credit card.