ETag and Last-Modified headers should explain cache validation, not content truth

ETag and Last-Modified headers should explain cache validation, not content truth. They are useful technical signals for deciding whether a resource changed from the client or cache perspective, but they do not replace a readable source note about what changed and why it matters.

MDN describes ETag as an identifier for a specific version of a resource that can help caches avoid downloading unchanged content. MDN describes Last-Modified as the date and time the origin server believes the resource was last changed, and as a validator for conditional requests. Those signals are valuable for bandwidth, caching, and version comparison. They are less useful when a reader needs to understand whether a policy, price, statistic, or cited statement changed in substance.

A practical source check can store URL, retrieved date, ETag, Last-Modified, response status, content hash if used, observed title, and the claim being supported. If ETag changes but the cited section did not, the note should avoid overstating the change. If Last-Modified stays the same but visible content differs, the trail should record the discrepancy instead of trusting the header blindly.

The right interpretation is layered. HTTP validators tell a client whether to re-fetch or compare a resource. Source notes tell a human what evidence was seen, which claim depended on it, and when the claim should be checked again.

ETag and Last-Modified headers should explain cache validation, not content truth

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