Developer tools

API Request Timing Simulator

Measure DNS, TCP, TLS, TTFB and download timings for a real URL, or drag sliders to simulate any timing profile — both render the same color-coded waterfall chart.

Enter any URL and press Measure. Same-origin URLs give the most detail.

All measuring and simulating happens locally in your browser.

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Real browser timing

Uses the Resource Timing API to read genuine DNS, TCP, TLS, TTFB and download phases for a URL you fetch.

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Honest about limits

When a cross-origin server hides timing detail, the tool says so instead of guessing at numbers it cannot see.

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Always-on simulator

Drag five sliders to explore any timing profile, even when real measurement is restricted by the browser.

How to use the API request timing simulator

Pick whichever mode fits what you're trying to learn: real-world measurement or a controlled thought experiment.

  1. Choose a modeSwitch between Measure a real URL and Simulate custom timings at the top of the tool.
  2. Enter a URL or set slidersType an endpoint and press Measure, or drag the DNS, TCP, TLS, TTFB and download sliders.
  3. Read the waterfallEach phase is color-coded and labeled with its millisecond duration, plus the total request time.

Understanding request timing phases

Every network request moves through the same handful of stages before your data arrives. Seeing them broken out, instead of a single blended number, makes it obvious where time is actually being spent and which phase is worth optimizing.

DNS lookup

Translating a hostname into an IP address. Repeated requests to the same host are usually much faster here thanks to DNS caching.

TCP connect

The handshake that opens a raw connection between your browser and the server, before any encryption or data exchange happens.

TLS negotiation

For HTTPS, an extra round trip (or more) to agree on encryption keys. This phase is skipped entirely on plain HTTP connections.

TTFB and download

TTFB is server processing plus network latency before the first byte arrives. Download is the time spent streaming the rest of the response body.

API request timing simulator FAQ

Questions about measurement limits, timing phases and privacy.

Why does measuring a real URL sometimes only show a total duration?

Browsers only expose detailed DNS, TCP, TLS and TTFB timings for cross-origin requests when the server sends a Timing-Allow-Origin header. Without it, the Resource Timing API zeroes out the individual phases and only the overall duration is available, which this tool shows along with an explanation.

What is TTFB and why does it matter?

TTFB (time to first byte) is the gap between the browser finishing its request and the first byte of the response arriving. It reflects server processing time and network latency, and is often the biggest lever for perceived API speed.

What is the difference between the TCP and TLS phases?

TCP connect time is the handshake that opens a raw connection to the server. TLS negotiation happens afterward, on top of that connection, to agree on encryption for HTTPS. Plain HTTP requests skip the TLS phase entirely.

Does this tool send my requests through a server?

No. The Measure tab uses your own browser's fetch and Performance API to time a request it makes directly. Nothing passes through My Panda Toolbox's servers.

Is my data saved or sent anywhere?

No. Measured and simulated timings stay in your browser tab and are never stored or transmitted.

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