diff --git a/tools/profile.mjs b/tools/profile.mjs
index b8eeb2fa2c..d426e4456c 100644
--- a/tools/profile.mjs
+++ b/tools/profile.mjs
@@ -27,16 +27,22 @@
 
 import { CodeMap, CodeEntry } from "./codemap.mjs";
 import { ConsArray } from "./consarray.mjs";
+import { WebInspector } from "./sourcemap.mjs";
 
 // Used to associate log entries with source positions in scripts.
 // TODO: move to separate modules
 export class SourcePosition {
+  script = null;
+  line = -1;
+  column = -1;
+  entries = [];
+  isFunction = false;
+  originalPosition = undefined;
+
   constructor(script, line, column) {
     this.script = script;
     this.line = line;
     this.column = column;
-    this.entries = [];
-    this.isFunction = false;
   }
 
   addEntry(entry) {
@@ -66,9 +72,11 @@ export class Script {
   url;
   source;
   name;
+  sourcePosition = undefined;
   // Map<line, Map<column, SourcePosition>>
   lineToColumn = new Map();
   _entries = [];
+  _sourceMapState = "unknown";
 
   constructor(id) {
     this.id = id;
@@ -89,6 +97,14 @@ export class Script {
     return this._entries;
   }
 
+  get startLine() {
+    return this.sourcePosition?.line ?? 1;
+  }
+
+  get sourceMapState() {
+    return this._sourceMapState;
+  }
+
   findFunctionSourcePosition(sourcePosition) {
     // TODO(cbruni) implmenent
     return undefined;
@@ -100,6 +116,10 @@ export class Script {
       sourcePosition = new SourcePosition(this, line, column,)
       this._addSourcePosition(line, column, sourcePosition);
     }
+    if (entry.entry?.type == "Script") {
+      // Mark the source position of scripts, for inline scripts which
+      this.sourcePosition = sourcePosition;
+    }
     sourcePosition.addEntry(entry);
     this._entries.push(entry);
     return sourcePosition;
@@ -149,6 +169,67 @@ export class Script {
     matchingScripts.push(script);
     return url;
   }
+
+  ensureSourceMapCalculated(sourceMapFetchPrefix=undefined) {
+    if (this._sourceMapState !== "unknown") return;
+
+    const sourceMapURLMatch =
+        this.source.match(/\/\/# sourceMappingURL=(.*)\n/);
+    if (!sourceMapURLMatch) {
+      this._sourceMapState = "none";
+      return;
+    }
+
+    this._sourceMapState = "loading";
+    let sourceMapURL = sourceMapURLMatch[1];
+    (async () => {
+      try {
+        let sourceMapPayload;
+        try {
+          sourceMapPayload = await fetch(sourceMapURL);
+        } catch (e) {
+          if (e instanceof TypeError && sourceMapFetchPrefix) {
+            // Try again with fetch prefix.
+            // TODO(leszeks): Remove the retry once the prefix is
+            // configurable.
+            sourceMapPayload =
+                await fetch(sourceMapFetchPrefix + sourceMapURL);
+          } else {
+            throw e;
+          }
+        }
+        sourceMapPayload = await sourceMapPayload.text();
+
+        if (sourceMapPayload.startsWith(')]}')) {
+          sourceMapPayload =
+              sourceMapPayload.substring(sourceMapPayload.indexOf('\n'));
+        }
+        sourceMapPayload = JSON.parse(sourceMapPayload);
+        const sourceMap =
+            new WebInspector.SourceMap(sourceMapURL, sourceMapPayload);
+
+        const startLine = this.startLine;
+        for (const sourcePosition of this.sourcePositions) {
+          const line = sourcePosition.line - startLine;
+          const column = sourcePosition.column - 1;
+          const mapping = sourceMap.findEntry(line, column);
+          if (mapping) {
+            sourcePosition.originalPosition = {
+              source: new URL(mapping[2], sourceMapURL).href,
+              line: mapping[3] + 1,
+              column: mapping[4] + 1
+            };
+          } else {
+            sourcePosition.originalPosition = {source: null, line:0, column:0};
+          }
+        }
+        this._sourceMapState = "loaded";
+      } catch (e) {
+        console.error(e);
+        this._sourceMapState = "failed";
+      }
+    })();
+  }
 }
 
 
diff --git a/tools/sourcemap.mjs b/tools/sourcemap.mjs
index 8ddab13cb7..ca0f8b98bb 100644
--- a/tools/sourcemap.mjs
+++ b/tools/sourcemap.mjs
@@ -326,7 +326,7 @@ WebInspector.SourceMap.prototype = {
         } while (digit & this._VLQ_CONTINUATION_MASK);
 
         // Fix the sign.
-        const negative = result & 1;
+        const negate = result & 1;
         // Use unsigned right shift, so that the 32nd bit is properly shifted
         // to the 31st, and the 32nd becomes unset.
         result >>>= 1;
diff --git a/tools/system-analyzer/helper.mjs b/tools/system-analyzer/helper.mjs
index 1eccfbdc93..359bbcdd98 100644
--- a/tools/system-analyzer/helper.mjs
+++ b/tools/system-analyzer/helper.mjs
@@ -26,6 +26,17 @@ export function delay(time) {
   return new Promise(resolver => setTimeout(resolver, time));
 }
 
+export function defer() {
+  let resolve_func, reject_func;
+  const p = new Promise((resolve, reject) => {
+    resolve_func = resolve;
+    reject_func = resolve;
+  });
+  p.resolve = resolve_func;
+  p.reject = reject_func;
+  return p;
+}
+
 export class Group {
   constructor(key, id, parentTotal, entries) {
     this.key = key;
diff --git a/tools/system-analyzer/index.mjs b/tools/system-analyzer/index.mjs
index 97fc4a2e26..030c72b690 100644
--- a/tools/system-analyzer/index.mjs
+++ b/tools/system-analyzer/index.mjs
@@ -312,7 +312,8 @@ class App {
 
   handleToolTip(event) {
     let content = event.content;
-    if (typeof content !== 'string') {
+    if (typeof content !== 'string' &&
+        !(content?.nodeType && content?.nodeName)) {
       content = content?.toolTipDict;
     }
     if (!content) {
diff --git a/tools/system-analyzer/view/helper.mjs b/tools/system-analyzer/view/helper.mjs
index 92a8ff930e..f18eb6b135 100644
--- a/tools/system-analyzer/view/helper.mjs
+++ b/tools/system-analyzer/view/helper.mjs
@@ -123,13 +123,32 @@ export class CSSColor {
 }
 
 export class DOM {
-  static element(type, classes) {
+  static element(type, options) {
     const node = document.createElement(type);
-    if (classes !== undefined) {
-      if (typeof classes === 'string') {
-        node.className = classes;
+    if (options !== undefined) {
+      if (typeof options === 'string') {
+        // Old behaviour: options = class string
+        node.className = options;
+      } else if (Array.isArray(options)) {
+        // Old behaviour: options = class array
+        DOM.addClasses(node, options);
       } else {
-        DOM.addClasses(node, classes);
+        // New behaviour: options = attribute dict
+        for (const [key, value] of Object.entries(options)) {
+          if (key == 'className') {
+            node.className = value;
+          } else if (key == 'classList') {
+            node.classList = value;
+          } else if (key == 'textContent') {
+            node.textContent = value;
+          } else if (key == 'children') {
+            for (const child of value) {
+              node.appendChild(child);
+            }
+          } else {
+            node.setAttribute(key, value);
+          }
+        }
       }
     }
     return node;
@@ -158,20 +177,20 @@ export class DOM {
     return button;
   }
 
-  static div(classes) {
-    return this.element('div', classes);
+  static div(options) {
+    return this.element('div', options);
   }
 
-  static span(classes) {
-    return this.element('span', classes);
+  static span(options) {
+    return this.element('span', options);
   }
 
-  static table(classes) {
-    return this.element('table', classes);
+  static table(options) {
+    return this.element('table', options);
   }
 
-  static tbody(classes) {
-    return this.element('tbody', classes);
+  static tbody(options) {
+    return this.element('tbody', options);
   }
 
   static td(textOrNode, className) {
diff --git a/tools/system-analyzer/view/script-panel.mjs b/tools/system-analyzer/view/script-panel.mjs
index d90091bf5a..d9de7d4e52 100644
--- a/tools/system-analyzer/view/script-panel.mjs
+++ b/tools/system-analyzer/view/script-panel.mjs
@@ -1,17 +1,21 @@
 // Copyright 2020 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-import {groupBy} from '../helper.mjs';
+import {defer, groupBy} from '../helper.mjs';
 import {App} from '../index.mjs'
 
 import {SelectRelatedEvent, ToolTipEvent} from './events.mjs';
 import {CollapsableElement, CSSColor, delay, DOM, formatBytes, gradientStopsFromGroups} from './helper.mjs';
 
+// A source mapping proxy for source maps that don't have CORS headers.
+// TODO(leszeks): Make this configurable.
+const sourceMapFetchPrefix = 'http://localhost:8080/';
+
 DOM.defineCustomElement('view/script-panel',
                         (templateText) =>
                             class SourcePanel extends CollapsableElement {
   _selectedSourcePositions = [];
-  _sourcePositionsToMarkNodes = [];
+  _sourcePositionsToMarkNodesPromise = Promise.resolve([]);
   _scripts = [];
   _script;
 
@@ -34,6 +38,8 @@ DOM.defineCustomElement('view/script-panel',
   set script(script) {
     if (this._script === script) return;
     this._script = script;
+    script.ensureSourceMapCalculated(sourceMapFetchPrefix);
+    this._sourcePositionsToMarkNodesPromise = defer();
     this.requestUpdate();
   }
 
@@ -82,15 +88,19 @@ DOM.defineCustomElement('view/script-panel',
 
   async _renderSourcePanel() {
     let scriptNode;
-    if (this._script) {
+    const script = this._script;
+    if (script) {
       await delay(1);
+      if (script != this._script) return;
       const builder = new LineBuilder(this, this._script);
-      scriptNode = builder.createScriptNode();
-      this._sourcePositionsToMarkNodes = builder.sourcePositionToMarkers;
+      scriptNode = await builder.createScriptNode(this._script.startLine);
+      if (script != this._script) return;
+      this._sourcePositionsToMarkNodesPromise.resolve(
+          builder.sourcePositionToMarkers);
     } else {
       scriptNode = DOM.div();
       this._selectedMarkNodes = undefined;
-      this._sourcePositionsToMarkNodes = new Map();
+      this._sourcePositionsToMarkNodesPromise.resolve(new Map());
     }
     const oldScriptNode = this.script.childNodes[1];
     this.script.replaceChild(scriptNode, oldScriptNode);
@@ -98,22 +108,24 @@ DOM.defineCustomElement('view/script-panel',
 
   async _focusSelectedMarkers() {
     await delay(100);
+    const sourcePositionsToMarkNodes =
+        await this._sourcePositionsToMarkNodesPromise;
     // Remove all marked nodes.
-    for (let markNode of this._sourcePositionsToMarkNodes.values()) {
+    for (let markNode of sourcePositionsToMarkNodes.values()) {
       markNode.className = '';
     }
     for (let sourcePosition of this._selectedSourcePositions) {
       if (sourcePosition.script !== this._script) continue;
-      this._sourcePositionsToMarkNodes.get(sourcePosition).className = 'marked';
+      sourcePositionsToMarkNodes.get(sourcePosition).className = 'marked';
     }
-    this._scrollToFirstSourcePosition()
+    this._scrollToFirstSourcePosition(sourcePositionsToMarkNodes)
   }
 
-  _scrollToFirstSourcePosition() {
+  _scrollToFirstSourcePosition(sourcePositionsToMarkNodes) {
     const sourcePosition = this._selectedSourcePositions.find(
         each => each.script === this._script);
     if (!sourcePosition) return;
-    const markNode = this._sourcePositionsToMarkNodes.get(sourcePosition);
+    const markNode = sourcePositionsToMarkNodes.get(sourcePosition);
     markNode.scrollIntoView(
         {behavior: 'auto', block: 'center', inline: 'center'});
   }
@@ -135,7 +147,8 @@ DOM.defineCustomElement('view/script-panel',
   }
 
   handleSourcePositionMouseOver(e) {
-    const entries = e.target.sourcePosition.entries;
+    const sourcePosition = e.target.sourcePosition;
+    const entries = sourcePosition.entries;
     let text = groupBy(entries, each => each.constructor, true)
                    .map(group => {
                      let text = `${group.key.name}: ${group.count}\n`
@@ -147,7 +160,46 @@ DOM.defineCustomElement('view/script-panel',
                      return text;
                    })
                    .join('\n');
-    this.dispatchEvent(new ToolTipEvent(text, e.target));
+
+    let sourceMapContent;
+    switch (this._script.sourceMapState) {
+      case 'loaded': {
+        const originalPosition = sourcePosition.originalPosition;
+        if (originalPosition.source === null) {
+          sourceMapContent =
+              DOM.element('i', {textContent: 'no source mapping for location'});
+        } else {
+          sourceMapContent = DOM.element('a', {
+            href: `${originalPosition.source}`,
+            target: '_blank',
+            textContent: `${originalPosition.source}:${originalPosition.line}:${
+                originalPosition.column}`
+          });
+        }
+        break;
+      }
+      case 'loading':
+        sourceMapContent =
+            DOM.element('i', {textContent: 'source map still loading...'});
+        break;
+      case 'failed':
+        sourceMapContent =
+            DOM.element('i', {textContent: 'source map failed to load'});
+        break;
+      case 'none':
+        sourceMapContent = DOM.element('i', {textContent: 'no source map'});
+        break;
+      default:
+        break;
+    }
+
+    const toolTipContent = DOM.div({
+      children: [
+        DOM.element('pre', {className: 'textContent', textContent: text}),
+        sourceMapContent
+      ]
+    });
+    this.dispatchEvent(new ToolTipEvent(toolTipContent, e.target));
   }
 });
 
@@ -214,49 +266,42 @@ class LineBuilder {
   _script;
   _clickHandler;
   _mouseoverHandler;
-  _sourcePositions;
   _sourcePositionToMarkers = new Map();
 
   constructor(panel, script) {
     this._script = script;
     this._clickHandler = panel.handleSourcePositionClick.bind(panel);
     this._mouseoverHandler = panel.handleSourcePositionMouseOver.bind(panel);
-    // TODO: sort on script finalization.
-    script.sourcePositions.sort((a, b) => {
-      if (a.line === b.line) return a.column - b.column;
-      return a.line - b.line;
-    });
-    this._sourcePositions = new SourcePositionIterator(script.sourcePositions);
   }
 
   get sourcePositionToMarkers() {
     return this._sourcePositionToMarkers;
   }
 
-  createScriptNode() {
+  async createScriptNode(startLine) {
     const scriptNode = DOM.div('scriptNode');
-    let startLine = 1;
-    // Try to infer the start line of the script from its code entries.
-    for (const entry of this._script.entries) {
-      if (entry.type.startsWith('Script')) {
-        if (entry.sourcePosition) {
-          startLine = entry.sourcePosition.line;
-        }
-        break;
-      }
-    }
+
+    // TODO: sort on script finalization.
+    this._script.sourcePositions.sort((a, b) => {
+      if (a.line === b.line) return a.column - b.column;
+      return a.line - b.line;
+    });
+
+    const sourcePositionsIterator =
+        new SourcePositionIterator(this._script.sourcePositions);
     scriptNode.style.counterReset = `sourceLineCounter ${startLine - 1}`;
     for (let [lineIndex, line] of lineIterator(
              this._script.source, startLine)) {
-      scriptNode.appendChild(this._createLineNode(lineIndex, line));
+      scriptNode.appendChild(
+          this._createLineNode(sourcePositionsIterator, lineIndex, line));
     }
     return scriptNode;
   }
 
-  _createLineNode(lineIndex, line) {
+  _createLineNode(sourcePositionsIterator, lineIndex, line) {
     const lineNode = DOM.span();
     let columnIndex = 0;
-    for (const sourcePosition of this._sourcePositions.forLine(lineIndex)) {
+    for (const sourcePosition of sourcePositionsIterator.forLine(lineIndex)) {
       const nextColumnIndex = sourcePosition.column - 1;
       lineNode.appendChild(document.createTextNode(
           line.substring(columnIndex, nextColumnIndex)));
@@ -280,10 +325,14 @@ class LineBuilder {
     marker.onmouseover = this._mouseoverHandler;
 
     const entries = sourcePosition.entries;
-    const stops = gradientStopsFromGroups(
-        entries.length, '%', groupBy(entries, entry => entry.constructor),
-        type => LineBuilder.colorMap.get(type));
-    marker.style.backgroundImage = `linear-gradient(0deg,${stops.join(',')})`
+    const groups = groupBy(entries, entry => entry.constructor);
+    if (groups.length > 1) {
+      const stops = gradientStopsFromGroups(
+          entries.length, '%', groups, type => LineBuilder.colorMap.get(type));
+      marker.style.backgroundImage = `linear-gradient(0deg,${stops.join(',')})`
+    } else {
+      marker.style.backgroundColor = LineBuilder.colorMap.get(groups[0].key)
+    }
 
     return marker;
   }
diff --git a/tools/system-analyzer/view/tool-tip.mjs b/tools/system-analyzer/view/tool-tip.mjs
index 84ee99a44a..5be98ae214 100644
--- a/tools/system-analyzer/view/tool-tip.mjs
+++ b/tools/system-analyzer/view/tool-tip.mjs
@@ -90,7 +90,7 @@ DOM.defineCustomElement(
         if (typeof content === 'string') {
           this.contentNode.innerHTML = content;
           this.contentNode.className = 'textContent';
-        } else if (content?.nodeType && nodeType?.nodeName) {
+        } else if (content?.nodeType && content?.nodeName) {
           this._setContentNode(content);
         } else {
           if (this.contentNode.firstChild?.localName == 'property-link-table') {