--- title: Unattributed Navigation Overhead (UNO) Is Underrated –... description: Unattributed Navigation Overhead (UNO), a concept coined by Tim Vereecke, is the portion of Time to First Byte left over after subtracting the redirect, DNS,... canonical: https://daily.dev/posts/unattributed-navigation-overhead-uno-is-underrated-css-wizardry-7pihq86rv twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Unattributed Navigation Overhead (UNO) Is Underrated – CSS Wizardry | daily.dev og:description: Unattributed Navigation Overhead (UNO), a concept coined by Tim Vereecke, is the portion of Time to First Byte left over after subtracting the redirect, DNS,... og:url: https://daily.dev/posts/unattributed-navigation-overhead-uno-is-underrated-css-wizardry-7pihq86rv og:image: https://api.daily.dev/og/posts/7pihq86Rv.png og:image:alt: Unattributed Navigation Overhead (UNO) Is Underrated – CSS Wizardry og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Unattributed Navigation Overhead (UNO) Is Underrated – CSS Wizardry **[CSS Wizardry](https://daily.dev/sources/csswizardry)** · [@csswizardry](https://daily.dev/csswizardry) · 11 min read · 3 upvotes · 0 comments ## Summary Unattributed Navigation Overhead (UNO), a concept coined by Tim Vereecke, is the portion of Time to First Byte left over after subtracting the redirect, DNS, connection, and request-response phases reported by the Navigation Timing API. Because cross-origin redirects reset redirect timing to zero, hidden redirects (tracking links, shorteners, http-to-https jumps) inflate TTFB invisibly. A real-world SpeedCurve dataset showed 7.1 million UNO observations versus only 166 detectable redirects, illustrating how much navigation time goes unexplained. Chrome 151 introduces a Timing-Allow-Origin opt-in that lets destination origins see cross-origin redirect timing, but this only partially addresses the problem since not all providers will adopt it and UNO includes other browser-side delays too. The piece recommends tracking UNO as a first-class RUM metric alongside TTFB and its components. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What is Unattributed Navigation Overhead (UNO) in web performance monitoring? Unattributed Navigation Overhead is the portion of Time to First Byte remaining after subtracting the redirect, DNS, connection, and request-to-response phases exposed by the Navigation Timing API. It is calculated as TTFB minus redirect minus DNS minus connection minus request-to-response-start, and often includes hidden cross-origin redirects, browser initialization delays, cache access, and resource contention. _Teams chasing unexplained TTFB regressions can compare notes on RUM setups like this via daily.dev._ ### Why does Navigation Timing show zero redirects even when a cross-origin redirect happened? For privacy reasons, Navigation Timing traditionally sets redirectStart, redirectEnd, and redirectCount to zero whenever any redirect in the chain crosses an origin boundary, even though the overall TTFB still includes that redirect's time. This means routine journeys like ad-tracking redirects, URL shorteners, or an http-to-https scheme change can vanish entirely from redirect breakdowns despite consuming real time. _Anyone debugging invisible redirect overhead can dig into Navigation Timing quirks like this via daily.dev._ ### How does Chrome 151 change visibility into cross-origin redirect timing? Chrome 151 began rolling out a cross-origin redirect timing opt-in that lets redirecting servers use the Timing-Allow-Origin header to permit the destination origin to measure redirects under their control. This does not make Unattributed Navigation Overhead obsolete, since every server in a chain must opt in, existing shorteners and campaign platforms may not add the header, and other UNO sources like browser delays remain invisible. _Developers tracking browser timing API changes can follow Chrome release updates like this via daily.dev._ ## Similar posts on daily.dev - [Web-Perf Wednesday 002 – The Metrics Don’t Tell the Whole Story – CSS Wizardry](https://daily.dev/posts/web-perf-wednesday-002-the-metrics-don-t-tell-the-whole-story-css-wizardry-757w9utar) · CSS Wizardry · 4 upvotes · 0 comments - [Insights from 100 site speed reviews in 2025](https://daily.dev/posts/insights-from-100-site-speed-reviews-in-2025-yh4tk3cne) · Web Performance Calendar · 0 upvotes · 0 comments - [Introducing LUX Sidecar: Your SpeedCurve Companion – CSS Wizardry](https://daily.dev/posts/introducing-lux-sidecar-your-speedcurve-companion-css-wizardry-tdkjc6uss) · CSS Wizardry · 4 upvotes · 0 comments - [Final Soft Navigations origin trial starting in Chrome 147](https://daily.dev/posts/final-soft-navigations-origin-trial-starting-in-chrome-147-tietnqt8l) · Chrome Developers · 1 upvotes · 0 comments - [Chris’ Corner: HTML](https://daily.dev/posts/chris-corner-html-vq7rlmfuk) · CodePen · 25 upvotes · 0 comments --- Tags: [#webdev](https://daily.dev/tags/webdev), [#google-chrome](https://daily.dev/tags/google-chrome) [View this post on daily.dev](https://daily.dev/posts/unattributed-navigation-overhead-uno-is-underrated-css-wizardry-7pihq86rv) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Unattributed Navigation Overhead (UNO) Is Underrated – CSS Wizardry","url":"https://daily.dev/posts/unattributed-navigation-overhead-uno-is-underrated-css-wizardry-7pihq86rv","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/unattributed-navigation-overhead-uno-is-underrated-css-wizardry-7pihq86rv"},"datePublished":"2026-08-19T13:24:05.498Z","dateModified":"2026-09-13T22:00:17.043Z","description":"Unattributed Navigation Overhead (UNO), a concept coined by Tim Vereecke, is the portion of Time to First Byte left over after subtracting the redirect, DNS,...","image":"https://media.daily.dev/image/upload/s--ZrL_HSsR--/f_auto/v1722860399/public/Placeholder%2006","thumbnailUrl":"https://media.daily.dev/image/upload/s--ZrL_HSsR--/f_auto/v1722860399/public/Placeholder%2006","isAccessibleForFree":true,"articleSection":"CSS Wizardry","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Person","name":"Harry Roberts","url":"https://daily.dev/csswizardry","image":"https://media.daily.dev/image/upload/s--6zcMNpvC--/f_auto/v1755686282/avatars/avatar_Lw7jrTalrSeSbSjzuBQBH?_a=BAMClqZW0","interactionStatistic":{"@type":"InteractionCounter","interactionType":{"@type":"EndorseAction"},"userInteractionCount":230}},"commentCount":0,"discussionUrl":"https://daily.dev/posts/unattributed-navigation-overhead-uno-is-underrated-css-wizardry-7pihq86rv","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":3},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"webdev,google-chrome","timeRequired":"PT11M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"CSS Wizardry","item":"https://daily.dev/sources/csswizardry"},{"@type":"ListItem","position":3,"name":"Unattributed Navigation Overhead (UNO) Is Underrated – CSS Wizardry"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/unattributed-navigation-overhead-uno-is-underrated-css-wizardry-7pihq86rv#faq","mainEntity":[{"@type":"Question","name":"What is Unattributed Navigation Overhead (UNO) in web performance monitoring?","acceptedAnswer":{"@type":"Answer","text":"Unattributed Navigation Overhead is the portion of Time to First Byte remaining after subtracting the redirect, DNS, connection, and request-to-response phases exposed by the Navigation Timing API. It is calculated as TTFB minus redirect minus DNS minus connection minus request-to-response-start, and often includes hidden cross-origin redirects, browser initialization delays, cache access, and resource contention. Teams chasing unexplained TTFB regressions can compare notes on RUM setups like this via daily.dev."}},{"@type":"Question","name":"Why does Navigation Timing show zero redirects even when a cross-origin redirect happened?","acceptedAnswer":{"@type":"Answer","text":"For privacy reasons, Navigation Timing traditionally sets redirectStart, redirectEnd, and redirectCount to zero whenever any redirect in the chain crosses an origin boundary, even though the overall TTFB still includes that redirect's time. This means routine journeys like ad-tracking redirects, URL shorteners, or an http-to-https scheme change can vanish entirely from redirect breakdowns despite consuming real time. Anyone debugging invisible redirect overhead can dig into Navigation Timing quirks like this via daily.dev."}},{"@type":"Question","name":"How does Chrome 151 change visibility into cross-origin redirect timing?","acceptedAnswer":{"@type":"Answer","text":"Chrome 151 began rolling out a cross-origin redirect timing opt-in that lets redirecting servers use the Timing-Allow-Origin header to permit the destination origin to measure redirects under their control. This does not make Unattributed Navigation Overhead obsolete, since every server in a chain must opt in, existing shorteners and campaign platforms may not add the header, and other UNO sources like browser delays remain invisible. Developers tracking browser timing API changes can follow Chrome release updates like this via daily.dev."}}]} ```