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Collect email addresses with proof that the person actually asked to hear from you.
What it adds
An email capture form with a confirmation step, stored consent metadata, and a working unsubscribe.
What your agent is told to do
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What your agent is told to do
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Place the capture box where it makes sense and keep it to one field plus a button. Ask for a name only if you will actually use it.
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Send a confirmation email containing a signed, expiring link and only mark the subscriber active when it is clicked. Store the source, the timestamp, and the address of the request alongside the subscription as the record of consent.
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Reuse the app's existing Email Verification mechanism for the confirmation link rather than writing a second token scheme, and route unsubscribes through the existing Email Preference Center if one exists.
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If the app already syncs contacts to an external marketing platform, make this feature feed that same pipeline instead of creating a second list that immediately diverges.
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Do not add the address to your sending list before confirmation. Sending to unconfirmed addresses is how a domain's sending reputation is destroyed, and it is difficult to recover.
Edge cases it handles
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Edge cases it handles
8- A misspelled common domain silently loses the subscriber forever. Validate the address format and warn on near-miss domains before storing, while still allowing the user to override.
- Someone who signs up twice should see the same success message as a first-time signup. Telling them the address is already registered leaks who is on your list.
- Unconfirmed opt-in links must expire after a defined window, and the pending record should be cleaned up rather than sitting in the table forever.
- Every subscriber needs the source, exact timestamp, and consent context recorded. Without that you cannot answer a complaint or a regulator asking where the address came from.
- An address that has unsubscribed must not be silently reactivated by a later form submission. Treat the resubscribe as a deliberate act requiring a fresh confirmation.
- The unsubscribe link in every sent email must work without a login and must take effect immediately, not at the next send.
- The form is a spam target. Rate-limit by address and by session so it cannot be used to send confirmation emails to arbitrary third parties.
- Success and error states must be announced accessibly, and the form must not clear itself before the visitor has seen the confirmation message.
Definition of done
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Definition of done
9- An address becomes an active subscriber only after a confirmation link is clicked.
- Consent source, timestamp, and context are stored for every subscriber.
- Confirmation links expire after a defined window and expired attempts explain what to do next.
- A repeat signup returns the same success response as a first signup.
- A previously unsubscribed address is not reactivated without a fresh confirmation.
- Unsubscribe works from any sent email without a login and takes effect immediately.
- The form is rate-limited and cannot be used to mail arbitrary addresses.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Waitlist
Waitlist
Capture demand before you're ready to open the doors.
What it does
An email capture that gates access and lets you admit people in batches.
How it works
- 1 Add an email capture on the landing page, storing entries with a timestamp and source.
- 2 Give yourself an admin way to admit people, individually or in batches.
- 3 Send an email when someone is admitted, with a unique access link.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/waitlist
Quote Calculator
Quote Calculator
Let a visitor answer a few questions and get an honest price estimate on the spot.
What it does
A guided question flow that produces a priced estimate from server-held rules, with a saved copy for follow-up.
How it works
- 1 Build the question flow on the app's existing Multi-Step Form and Conditional Form Fields rather than a new one-off wizard. Showing and hiding questions based on earlier answers is exactly what conditional fields already do.
- 2 Keep every rate, multiplier, minimum, and discount on the server. The browser sends answers and receives a priced breakdown; it never holds the price list and never does the arithmetic that produces the total.
- 3 Show the estimate as itemised lines with a total, not a single number. A visitor who can see which answer added which cost will trust the figure and will adjust an answer instead of leaving.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/quote-calculator
Experiment Assignment
Experiment Assignment
Put each user in one experiment bucket and keep them there.
What it does
Deterministic, stable assignment of users to experiment variants, with eligibility rules and protection against overlapping tests.
How it works
- 1 Assign by hashing a stable identity key together with the experiment key. Assignment must be computed, not stored and looked up, so the same user always lands in the same bucket.
- 2 Pick the identity key deliberately: an account id where one exists, a durable anonymous id otherwise. Never assign on session id — a new session becomes a new user.
- 3 Define eligibility as an explicit filter applied before assignment: exclude staff, known bots, and plans the variant cannot apply to.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/experiment-assignment
How it works
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1
Copy the link
Grab the Markdown instruction URL for this feature.
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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.