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HTTP Conditional Requests: ETag, If-None-Match, If-Modified-Since and 304 Responses for Cheap Polling

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Self-Hosting & Infra intermediate 5 min read $0.01 Updated 2026-10-20

Tested against a local server: 200 with ETag, Last-Modified and Cache-Control; the same URL returning 304 with zero body bytes for a matching If-None-Match or If-Modified-Since; a stale ETag returning the full 200; and how to cache safely.

Stop re-downloading unchanged data. Send If-None-Match with the ETag you stored, handle 304 Not Modified with an empty body, and understand how Last-Modified, Cache-Control and stale validators behave.

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#http#etag#caching#polling#api

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