Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases #21817

Closed
#21844
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Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases#21817
#21844
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Lms24
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BrowserImprovementjavascriptPull requests that update javascript code

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@Lms24
Lms24
opened on Jun 26, 2026

Description

Our browserSessionIntegration sends a session envelope request directly in setupOnce (i.e. during Sentry.init()). While the SDK does not block init on the request, it invokes the processing and sending pipeline. This adds overhead. Moreover, a request leaving the web app this early has influence on the browser's network. We could demonstrate this in our Lighthouse performance tests, where we observed that especially under Ligththouse Lantern test mode, the additional request drastically increases the test app's LCP and decreases LH performance scores.

We can quite easily defer sending the session envelope. We still start the session right away (no harm in that, and arguably, that's the correct thing to do) but we call captureSession either via requestIdleCallback or via a ~5s timeout (TBD). Obviously, this should still happen "soon" after the pageload to avoid loosing out on short user sessions.

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    , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
     blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

    Skip to content
    Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases #21817
    Closed
    #21844
    Closed
    Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases#21817
    #21844
    Assignees
    Lms24
    Labels
    BrowserImprovementjavascriptPull requests that update javascript code
    Description
    @Lms24
    Lms24
    opened on Jun 26, 2026
    Description
    Our browserSessionIntegration sends a session envelope request directly in setupOnce (i.e. during Sentry.init()). While the SDK does not block init on the request, it invokes the processing and sending pipeline. This adds overhead. Moreover, a request leaving the web app this early has influence on the browser's network. We could demonstrate this in our Lighthouse performance tests, where we observed that especially under Ligththouse Lantern test mode, the additional request drastically increases the test app's LCP and decreases LH performance scores.
    We can quite easily defer sending the session envelope. We still start the session right away (no harm in that, and arguably, that's the correct thing to do) but we call captureSession either via requestIdleCallback or via a ~5s timeout (TBD). Obviously, this should still happen "soon" after the pageload to avoid loosing out on short user sessions.
    Image
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

      Skip to content
      Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases #21817
      Closed
      #21844
      Closed
      Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases#21817
      #21844
      Assignees
      Lms24
      Labels
      BrowserImprovementjavascriptPull requests that update javascript code
      Description
      @Lms24
      Lms24
      opened on Jun 26, 2026
      Description
      Our browserSessionIntegration sends a session envelope request directly in setupOnce (i.e. during Sentry.init()). While the SDK does not block init on the request, it invokes the processing and sending pipeline. This adds overhead. Moreover, a request leaving the web app this early has influence on the browser's network. We could demonstrate this in our Lighthouse performance tests, where we observed that especially under Ligththouse Lantern test mode, the additional request drastically increases the test app's LCP and decreases LH performance scores.
      We can quite easily defer sending the session envelope. We still start the session right away (no harm in that, and arguably, that's the correct thing to do) but we call captureSession either via requestIdleCallback or via a ~5s timeout (TBD). Obviously, this should still happen "soon" after the pageload to avoid loosing out on short user sessions.
      Image
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      Metadata
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      BrowserImprovementjavascriptPull requests that update javascript code
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

        Skip to content
        Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases #21817
        Closed
        #21844
        Closed
        Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases#21817
        #21844
        Assignees
        Lms24
        Labels
        BrowserImprovementjavascriptPull requests that update javascript code
        Description
        @Lms24
        Lms24
        opened on Jun 26, 2026
        Description
        Our browserSessionIntegration sends a session envelope request directly in setupOnce (i.e. during Sentry.init()). While the SDK does not block init on the request, it invokes the processing and sending pipeline. This adds overhead. Moreover, a request leaving the web app this early has influence on the browser's network. We could demonstrate this in our Lighthouse performance tests, where we observed that especially under Ligththouse Lantern test mode, the additional request drastically increases the test app's LCP and decreases LH performance scores.
        We can quite easily defer sending the session envelope. We still start the session right away (no harm in that, and arguably, that's the correct thing to do) but we call captureSession either via requestIdleCallback or via a ~5s timeout (TBD). Obviously, this should still happen "soon" after the pageload to avoid loosing out on short user sessions.
        Image
        Metadata
        Metadata
        Assignees
        Labels
        BrowserImprovementjavascriptPull requests that update javascript code
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          No milestone
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          None yet
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          No branches or pull requests
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

          Skip to content
          Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases #21817
          Closed
          #21844
          Closed
          Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases#21817
          #21844
          Assignees
          Lms24
          Labels
          BrowserImprovementjavascriptPull requests that update javascript code
          Description
          @Lms24
          Lms24
          opened on Jun 26, 2026
          Description
          Our browserSessionIntegration sends a session envelope request directly in setupOnce (i.e. during Sentry.init()). While the SDK does not block init on the request, it invokes the processing and sending pipeline. This adds overhead. Moreover, a request leaving the web app this early has influence on the browser's network. We could demonstrate this in our Lighthouse performance tests, where we observed that especially under Ligththouse Lantern test mode, the additional request drastically increases the test app's LCP and decreases LH performance scores.
          We can quite easily defer sending the session envelope. We still start the session right away (no harm in that, and arguably, that's the correct thing to do) but we call captureSession either via requestIdleCallback or via a ~5s timeout (TBD). Obviously, this should still happen "soon" after the pageload to avoid loosing out on short user sessions.
          Image
          Metadata
          Metadata
          Assignees
          Labels
          BrowserImprovementjavascriptPull requests that update javascript code
          Projects
          No projects
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            No milestone
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            None yet
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            No branches or pull requests
            Issue actions
            
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

            Skip to content
            Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases #21817
            Closed
            #21844
            Closed
            Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases#21817
            #21844
            Assignees
            Lms24
            Labels
            BrowserImprovementjavascriptPull requests that update javascript code
            Description
            @Lms24
            Lms24
            opened on Jun 26, 2026
            Description
            Our browserSessionIntegration sends a session envelope request directly in setupOnce (i.e. during Sentry.init()). While the SDK does not block init on the request, it invokes the processing and sending pipeline. This adds overhead. Moreover, a request leaving the web app this early has influence on the browser's network. We could demonstrate this in our Lighthouse performance tests, where we observed that especially under Ligththouse Lantern test mode, the additional request drastically increases the test app's LCP and decreases LH performance scores.
            We can quite easily defer sending the session envelope. We still start the session right away (no harm in that, and arguably, that's the correct thing to do) but we call captureSession either via requestIdleCallback or via a ~5s timeout (TBD). Obviously, this should still happen "soon" after the pageload to avoid loosing out on short user sessions.
            Image
            Metadata
            Metadata
            Assignees
            Labels
            BrowserImprovementjavascriptPull requests that update javascript code
            Projects
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              No milestone
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              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases #21817
              Closed
              #21844
              Closed
              Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases#21817
              #21844
              Assignees
              Lms24
              Labels
              BrowserImprovementjavascriptPull requests that update javascript code
              Description
              @Lms24
              Lms24
              opened on Jun 26, 2026
              Description
              Our browserSessionIntegration sends a session envelope request directly in setupOnce (i.e. during Sentry.init()). While the SDK does not block init on the request, it invokes the processing and sending pipeline. This adds overhead. Moreover, a request leaving the web app this early has influence on the browser's network. We could demonstrate this in our Lighthouse performance tests, where we observed that especially under Ligththouse Lantern test mode, the additional request drastically increases the test app's LCP and decreases LH performance scores.
              We can quite easily defer sending the session envelope. We still start the session right away (no harm in that, and arguably, that's the correct thing to do) but we call captureSession either via requestIdleCallback or via a ~5s timeout (TBD). Obviously, this should still happen "soon" after the pageload to avoid loosing out on short user sessions.
              Image
              Metadata
              Metadata
              Assignees
              Labels
              BrowserImprovementjavascriptPull requests that update javascript code
              Projects
              No projects
                Milestone
                No milestone
                Relationships
                None yet
                Development
                No branches or pull requests
                Issue actions
                
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

                Skip to content
                Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases #21817
                Closed
                #21844
                Closed
                Browser Session envelope is sent directly at SDK init time, causing SDK overhead increases#21817
                #21844
                Assignees
                Lms24
                Labels
                BrowserImprovementjavascriptPull requests that update javascript code
                Description
                @Lms24
                Lms24
                opened on Jun 26, 2026
                Description
                Our browserSessionIntegration sends a session envelope request directly in setupOnce (i.e. during Sentry.init()). While the SDK does not block init on the request, it invokes the processing and sending pipeline. This adds overhead. Moreover, a request leaving the web app this early has influence on the browser's network. We could demonstrate this in our Lighthouse performance tests, where we observed that especially under Ligththouse Lantern test mode, the additional request drastically increases the test app's LCP and decreases LH performance scores.
                We can quite easily defer sending the session envelope. We still start the session right away (no harm in that, and arguably, that's the correct thing to do) but we call captureSession either via requestIdleCallback or via a ~5s timeout (TBD). Obviously, this should still happen "soon" after the pageload to avoid loosing out on short user sessions.
                Image
                Metadata
                Metadata
                Assignees
                Labels
                BrowserImprovementjavascriptPull requests that update javascript code
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions