Tool: HTTP Latency

HTTP Latency

Full HTTP request waterfall — DNS resolution, TCP connect, TLS handshake, TTFB, and download phases.

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What it does

Makes an HTTP/HTTPS request and uses URLSessionTaskMetrics to extract precise phase timings without any custom instrumentation.

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Interface

Element	Description
URL field	Full URL (with or without https://). Press Return to run.
Method	GET, POST, HEAD, PUT, DELETE
Run / Cancel	Execute request; red Cancel while in-flight
Run Again	Re-run the same URL from the result summary bar
History table	Previous results — click a row to restore URL + method

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Phase Breakdown

Phase	Measured From
DNS	domainLookupStartDate → domainLookupEndDate
TCP Connect	connectStartDate → connectEndDate
TLS Handshake	secureConnectionStartDate → secureConnectionEndDate
Request Sent	requestStartDate → requestEndDate
TTFB	requestEndDate → responseStartDate
Download	responseStartDate → responseEndDate
Total	DNS start → download end

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Summary Bar

Shown after a completed request:

• HTTP status code (color-coded: green 2xx, orange 3xx, red 4xx/5xx)
• Total time
• Response size
• IP address used
• Protocol (HTTP/1.1, HTTP/2, HTTP/3)

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Tips

• DNS = 0 ms usually means the hostname was already cached
• TLS > 200 ms on first request is normal; subsequent requests reuse the session
• Use HEAD method for latency checks without downloading the response body
• History table lets you compare repeated runs side by side
• Large download times with fast TTFB indicate the response body is large, not the server