Design a backend feature where users save search filters and receive alerts when new matching items appear.

Design saved searches and alerts

Designs saved filters, scheduled matching, alert delivery, and freshness trade-offs for search-driven product workflows.

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TL;DR

I would store the saved search as validated filter criteria owned by a user, not as arbitrary query text. A scheduled worker would evaluate active saved searches against new or changed items, create alert records, and send notifications through the normal notification system. The API would let users create, pause, edit, delete, and view recent matches.

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Search filter persistence, query validation, scheduled evaluation, alert deduplication, notification delivery, and freshness.

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Core answer
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Why this question matters
Saved alerts connect search, background jobs, and notifications. The interview value is in defining what gets saved, how often it runs, and how duplicate alerts are avoided.
I would store the saved search as validated filter criteria owned by a user, not as arbitrary query text. A scheduled worker would evaluate active saved searches against new or changed items, create alert records, and send notifications through the normal notification system. The API would let users create, pause, edit, delete, and view recent matches.
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Stronger answer
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I would avoid scanning every saved search against the entire dataset every minute. The design can use item change events, last-checked cursors, indexed timestamps, or batching by common filters. Alert records need deduplication so the same item is not sent repeatedly for the same saved search. Search filters need versioning or migration behavior when the product changes available fields.

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Details

Saving raw search query strings without validation.
Re-alerting the same item every time the job runs.
Ignoring authorization when sending alert content.
Running unbounded full scans for every saved search.

Design a backend feature where users save search filters and receive alerts when new matching items appear.

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