Optimistic Updates
Make actions feel instant while still recovering cleanly when the server disagrees.
What it adds
Apply the expected result of a mutation immediately, then reconcile with the server response or roll back.
What your agent is told to do
5
What your agent is told to do
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Apply optimism only to actions that almost always succeed and are cheap to reverse: toggles, reordering, renaming, adding a comment.
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Keep the pre-mutation value so a failure can restore exactly that, and no more.
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Give newly created records a temporary client identifier and swap it for the server identifier when the response lands, updating anything already referencing it.
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Show the pending item as pending. Instant does not mean pretending the write already reached the server.
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Do not apply optimism to payments, deletions of anything expensive to recreate, or actions with side effects the user cannot see. Wait for the server and say so.
Edge cases it handles
6
Edge cases it handles
6- A rollback must revert only its own mutation, leaving later successful changes to the same record intact.
- Responses arriving out of order must not overwrite a newer value with an older one. Sequence them.
- A permission or validation failure discovered on the server needs a real explanation, not a silent revert.
- The revert must not jump the scroll position or move the item the user is about to click.
- A mutation on an item the user has since navigated away from still has to report its failure somewhere.
- Repeated failures against the same record should stop being optimistic and fall back to waiting.
Definition of done
8
Definition of done
8- Eligible actions render immediately and show a pending state.
- A failure reverts only that mutation and explains what happened.
- Temporary client IDs are reconciled with server IDs, including in referencing views.
- Out-of-order responses cannot restore stale values.
- Reverts do not shift layout or scroll position.
- Irreversible and side-effecting actions are excluded by design.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Feedback Widget
Feedback Widget
Let anyone report a bug or send a comment from the page they are looking at.
What it does
An always-available launcher that opens a short feedback form and submits it with page context attached.
How it works
- 1 Put a single persistent launcher in one corner of the app and open a compact form in place. Do not route the user to a separate feedback page and lose the context they were about to describe.
- 2 Attach the current URL, the app version, the viewport size, the signed-in account, and a short trail of recent client errors automatically, so the reporter does not have to describe where they were.
- 3 Show the captured context to the user before they send it, in a collapsible section, and let them remove it. Silent collection of screen state is a trust problem.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/feedback-widget
Booking Page
Booking Page
A shareable page where someone picks an open time and confirms it in a few clicks.
What it does
A public scheduling page listing open slots, taking a booking, and confirming it to both sides.
How it works
- 1 Build the visitor path first: pick a date, see open times in their own zone, fill a short form, confirm, and receive an email with the details and a cancellation link. That is the minimum coherent version.
- 2 Derive open slots from the owner's availability rules and existing bookings on the server at request time. Do not trust a slot list the browser has been holding since page load.
- 3 Reuse the app's existing Time Zone-Aware Scheduling for conversion and storage, store every time as an absolute instant, and display it converted to the visitor's detected zone with the zone named on screen.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/booking-page
Date and Time Display Component
Date and Time Display Component
Render every date and time through one component so none of them are ambiguous.
What it does
A single shared way of displaying dates and times, covering absolute format, time zone, and optional relative phrasing.
How it works
- 1 Find every place the app renders a date or a time — tables, activity feeds, audit logs, exports, emails, tooltips — and route them all through one display path rather than formatting at each call site.
- 2 Never render an all-numeric date whose day and month could be swapped. Spell or abbreviate the month, or use an unambiguous ordering consistently, because a reader has no way to tell 04/07 from 07/04.
- 3 State the time zone whenever the value is a specific moment rather than a calendar day, and be explicit about whose zone it is — the viewer's, the record's, or the account's — rather than leaving it implied.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/date-and-time-display-component
How it works
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1
Copy the link
Grab the Markdown instruction URL for this feature.
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2
Give it to your AI
Paste it into Claude Code, Cursor, v0, Lovable — whatever you build with.
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It inspects, then implements
Your agent reads your existing app first, then adds the feature to fit it.
Works with your stack
These instructions are written to adapt. They tell the agent to detect your framework, match your existing design system, and reuse what you already have — rather than assuming a particular stack.
Need it tighter than that? Customize the feature and tell it exactly what you're running.