Let's start with what makes this comparison different from the others in this series: Crab.fit and WhenItWorks are the two most similar tools in the free group scheduling space. If you've used one, you've essentially understood the other. Both use availability grids. Both are completely free. Neither requires accounts from anyone. Both show a live heatmap of group overlap.
The differences are real but specific — and for most people comparing the two, the decision will come down to one or two features rather than a fundamentally different approach. This guide names those differences precisely so you can make the call quickly.
How similar are they, really?
Feature-by-feature similarity
For most casual group scheduling situations — a dinner, a game night, a team lunch, a reunion date poll — either tool will get you to the answer. The choice between them is a preference call, not a capability gap.
What Crab.fit does well
Crab.fit deserves genuine credit. It modernized the availability grid concept after When2Meet let the interface stagnate, and it did so as a free, open-source project sustained by donations rather than venture capital or subscription revenue. That's worth acknowledging.
Per-user timezone detection
When a participant opens a Crab.fit event, it detects their local timezone and lets them switch to it before marking availability. So if you create an event in Pacific Time and send it to someone in London, they'll see the time grid in their local time rather than yours. This reduces the chance of someone accidentally marking the wrong hours because they forgot to account for the time difference.
WhenItWorks uses a single event timezone set by the organizer. Everyone sees the same labels. For groups within the same timezone — a local friend group, a single-city team — the distinction is irrelevant. For groups spanning multiple time zones, Crab.fit handles it more gracefully.
Open source and community-maintained
Crab.fit's codebase is public on GitHub. For users who care about where their data goes, how the tool works under the hood, or who want to self-host it, open source is a meaningful differentiator. The community can inspect, contribute to, and fork the code — which is a level of transparency WhenItWorks doesn't offer.
Optional response password
When a participant submits their availability on Crab.fit, they can set an optional password tied to their name for that specific event. If they want to come back and edit their response later, they'll need that password — it prevents someone else from submitting or changing availability under the same name.
WhenItWorks works the same way. When a guest enters their first and last name to mark their availability, they can optionally set a password for that response. It's not a site account or a permanent password — it's scoped entirely to that one event, used only if the guest wants to return and edit their own availability. Both tools handle this identically.
Privacy-first event expiration
Crab.fit is built with event expiry as a first-class concept. An expiration date is set at the time the event is created, derived from the last date in the poll. Once that date passes, the event becomes read-only — responses can still be viewed but no new availability can be submitted. A regular cleanup job then purges expired events under the platform's retention rules. If you value tools where events have a defined lifespan tied to their actual purpose, this is a considered design choice rather than a limitation.
WhenItWorks also sets an expiration on events based on the last poll date, after which the event becomes read-only. The mechanics are similar: events are marked expired once their window has passed, and cleanup runs on a schedule. Neither tool holds event data indefinitely beyond its useful life.
Who Crab.fit is genuinely better for: Groups spanning multiple timezones, users who care about open source and data transparency, and developers who might want to self-host or contribute to the codebase.
Where WhenItWorks has the edge
Best time is flagged automatically
This is the most functionally significant difference between the two tools. Crab.fit shows a heatmap — the darker the color, the more people are free. But it doesn't explicitly tell you which slot is best. You hover over different regions, look at the colors, and decide for yourself. For small groups with obvious overlap, this is fine. For larger groups with nuanced heatmaps where multiple slots look similarly dark, it requires real interpretation effort.
WhenItWorks highlights the best available time slot automatically once enough responses are in. You don't have to read the heatmap — the answer is surfaced for you. For organizers who want a fast, definitive answer rather than a visualization to interpret, this removes the last step of manual work.
Why this matters more than it sounds:When you're coordinating a group dinner and the answer is "Wednesday at 7pm works for 8 out of 10 people," you want to see that stated clearly — not inferred from a color gradient. The best-time flag is especially useful when sharing results with the group: "WhenItWorks says Wednesday at 7pm" is more decisive than "look at the heatmap and it seems like Wednesday evening."
Clear respondent tracking
WhenItWorks shows a named list of who has and hasn't submitted their availability. You can see at a glance that eight of twelve people have responded and identify the four who haven't — making targeted follow-up easy. Crab.fit shows respondents in the heatmap but doesn't surface a clean list of missing responses, which makes it harder to know who to nudge without clicking through the grid.
Events don't auto-delete
The flip side of Crab.fit's privacy-conscious deletion policy is that events disappear after 3 months of inactivity. For most one-off events this isn't an issue — by the time 3 months have passed, you've long since picked a time and moved on. But if you want to revisit an event link, share it again later, or keep it as a reference, WhenItWorks doesn't have a deletion window.
The quick pick
Use WhenItWorks when...
You want the answer surfaced, not just the data
- ·You want the best time flagged automatically — no heatmap interpretation
- ·You want a clear list of who has and hasn't responded
- ·Your group is in the same or similar time zones
- ·You want events to persist without an expiry window
- ·You're organizing a casual group: friends, family, a club, a team
Use Crab.fit when...
You want open source and timezone precision
- ·Your group spans multiple time zones and you want automatic per-user conversion
- ·You care about open source and data transparency
- ·You're a developer who might want to self-host or contribute
Full feature comparison
| Feature | WhenItWorks | Crab.fit |
|---|---|---|
| Scheduling model | Availability grid | Availability grid |
| Free to use | Yes, always | Yes — donation supported |
| Account required | No — anyone | No — anyone |
| Live availability heatmap | Yes | Yes |
| Best time auto-flagged | Yes — highlighted automatically | No — read the heatmap yourself |
| Named respondent list | Yes — clear who's missing | Visible in heatmap, not listed |
| Per-user timezone detection | Single organizer timezone | Yes — auto-detects per participant |
| Open source | No | Yes — fully open source |
| Event expiration | Expires after last poll date — read-only, then cleaned up | Expires after last poll date — read-only, then purged on schedule |
| Response password | Optional — guests can set a password to protect their own response | Optional per participant |
| Calendar sync attempt | No | Exists, reported unreliable |
| Mobile experience | Designed for mobile | Works on mobile |
| Ads | None | None |
A note on Crab.fit's calendar sync
Crab.fit advertises the ability to sync with Google Calendar or Outlook to auto-populate your free times when marking availability. In practice, this feature has had reliability issues — at least one published review noted the Google Calendar option didn't work. It's worth being aware of before you build it into your workflow expectations. If it works for you, it's a convenient shortcut. If it doesn't, manual selection takes about 30 seconds anyway.
The honest bottom line
If you're evaluating Crab.fit and WhenItWorks side by side, the most useful framing isn't "which is better" — it's "which specific features matter for your situation."
If your group is across time zones and you want each participant to see times in their own local timezone automatically, Crab.fit is the better fit. If you want the best meeting slot flagged for you rather than left for you to interpret from a color gradient, WhenItWorks is cleaner. If open source matters to you, Crab.fit is the only choice. If you want named respondent tracking that clearly shows who's missing, WhenItWorks is more direct.
For pure same-timezone casual scheduling — dinners, game nights, team lunches, sports sessions — either tool will get you to the answer in roughly the same number of steps. You genuinely can't go wrong with either one. Try both in two minutes each and use whichever feels right.
Give WhenItWorks a try
Create a free event in under 60 seconds. No account needed for you or anyone you invite — and the best time is flagged automatically when responses are in.
Create your first event →Free forever · No sign-up required · Works on any device
Frequently asked questions
What is the difference between Crab.fit and WhenItWorks?
Both tools use a free availability grid where everyone marks their own free time and the best overlap surfaces on a live heatmap, with no accounts required. Both also offer an optional per-response password so guests can protect and edit their own availability. The main differences: WhenItWorks automatically flags the best time slot so you don't have to interpret the heatmap yourself, and shows a clear named list of who has and hasn't responded. Crab.fit is open source and offers per-user timezone detection.
Is Crab.fit free?
Yes. Crab.fit is completely free with no paid tiers, funded by optional donations. WhenItWorks is also completely free. Neither tool requires payment for any feature.
Does Crab.fit require an account?
No. Neither organizers nor participants need an account on Crab.fit. Participants enter a name when marking availability, with an optional password that lets them return and edit their own response for that event. WhenItWorks works the same way — no account for anyone, and guests can optionally set a password to protect and edit their own response.
Does Crab.fit delete events?
Crab.fit sets an expiration date at event creation based on the last date in the poll. Once that date passes the event becomes read-only, and the platform periodically purges expired events under its retention rules. WhenItWorks follows a similar model — events expire based on the last poll date, become read-only, and are cleaned up on a schedule. Neither tool stores event data indefinitely beyond its useful window.
Is Crab.fit open source?
Yes. Crab.fit's codebase is public on GitHub and open to community contributions. WhenItWorks is not open source. If transparency about how the tool works or the ability to self-host matters to you, Crab.fit is the only option in this comparison.
Which is better for international groups across time zones?
Crab.fit handles this more gracefully — it detects each participant's local timezone and lets them view the availability grid in their own time, reducing the chance of errors from manual timezone conversion. WhenItWorks uses a single event timezone set by the organizer. For groups all in the same or similar timezone, this distinction doesn't matter. For groups spanning three or more time zones, Crab.fit's approach is more convenient.