diff --git a/src/Web/autopilot-monitor-web/app/sessions/components/EventTimeline.tsx b/src/Web/autopilot-monitor-web/app/sessions/components/EventTimeline.tsx
index a3feda3d..d2a2d87c 100644
--- a/src/Web/autopilot-monitor-web/app/sessions/components/EventTimeline.tsx
+++ b/src/Web/autopilot-monitor-web/app/sessions/components/EventTimeline.tsx
@@ -3,10 +3,16 @@
 import { useState, useMemo } from "react";
 import { EnrollmentEvent, Session } from "@/types";
 import { normalizeEventDataForDisplay, shortenBuildHashInMessage } from "../utils/eventHelpers";
+import { buildEventSearchMatcher, parseEventSearchQuery } from "../utils/eventSearchQuery";
 import { getEnrichedOrLookup, formatErrorCode, type ErrorCodeEntry } from "@/utils/errorCodeMap";
 import { readTimeProvenance, classifyTimeJump, readClockChangeDeltaMs } from "@/lib/timeProvenance";
 import { formatDuration, formatUtcOffset } from "@/lib/formatting";
 
+const SEARCH_SYNTAX_HINT =
+  "Searches event type, message and source. Several terms are combined with AND. " +
+  "A leading minus hides matches, e.g. -app_install_progress. " +
+  'Quote a term to take it literally, e.g. "-1".';
+
 interface EventTimelineProps {
   filteredEvents: EnrollmentEvent[];
   events: EnrollmentEvent[];
@@ -60,14 +66,16 @@ export default function EventTimeline({
   const [searchQuery, setSearchQuery] = useState("");
   const [rawMode, setRawMode] = useState(false);
 
-  const matchesSearch = useMemo(() => {
-    if (!searchQuery.trim()) return null;
-    const q = searchQuery.toLowerCase();
-    return (event: EnrollmentEvent) =>
-      event.eventType?.toLowerCase().includes(q) ||
-      event.message?.toLowerCase().includes(q) ||
-      event.source?.toLowerCase().includes(q);
-  }, [searchQuery]);
+  // Terms are AND-ed, a leading minus excludes — see utils/eventSearchQuery.ts.
+  const matchesSearch = useMemo(() => buildEventSearchMatcher(searchQuery), [searchQuery]);
+  const excludedTerms = useMemo(() => parseEventSearchQuery(searchQuery).exclude, [searchQuery]);
+
+  // The counter has to follow the search, otherwise excluding event types leaves it
+  // reporting a number of rows the timeline no longer shows.
+  const searchVisibleCount = useMemo(
+    () => (matchesSearch ? filteredEvents.filter(matchesSearch).length : filteredEvents.length),
+    [filteredEvents, matchesSearch],
+  );
 
   const sortedBySequence = useMemo(() => {
     let filtered = events.filter(e => severityFilters.has(e.severity));
@@ -102,7 +110,8 @@ export default function EventTimeline({
             type="text"
             value={searchQuery}
             onChange={(e) => setSearchQuery(e.target.value)}
-            placeholder="Search events..."
+            placeholder="Search or -exclude..."
+            title={SEARCH_SYNTAX_HINT}
             className="w-full pl-7 pr-7 py-1 text-xs border border-gray-300 rounded-full focus:outline-none focus:ring-1 focus:ring-green-500 focus:border-green-500"
           />
           {searchQuery && (
@@ -139,7 +148,15 @@ export default function EventTimeline({
               </button>
             );
           })}
-          <span className="text-xs text-gray-400">({filteredEvents.length}/{events.length})</span>
+          <span className="text-xs text-gray-400">({searchVisibleCount}/{events.length})</span>
+          {excludedTerms.length > 0 && (
+            <span
+              className="px-2 py-0.5 text-xs font-medium rounded-full bg-gray-100 border border-gray-300 text-gray-600 max-w-[16rem] truncate"
+              title={`Events matching ${excludedTerms.map(t => `"${t}"`).join(", ")} are hidden.`}
+            >
+              hiding {excludedTerms.join(", ")}
+            </span>
+          )}
           <div className="flex gap-1.5 ml-auto items-center">
             <button
               onClick={() => setRawMode(!rawMode)}
diff --git a/src/Web/autopilot-monitor-web/app/sessions/utils/__tests__/eventSearchQuery.test.ts b/src/Web/autopilot-monitor-web/app/sessions/utils/__tests__/eventSearchQuery.test.ts
new file mode 100644
index 00000000..d0167dc1
--- /dev/null
+++ b/src/Web/autopilot-monitor-web/app/sessions/utils/__tests__/eventSearchQuery.test.ts
@@ -0,0 +1,119 @@
+import { describe, it, expect } from "vitest";
+import {
+  buildEventSearchMatcher,
+  parseEventSearchQuery,
+  type EventSearchFields,
+} from "../eventSearchQuery";
+
+const ev = (eventType: string, message = "", source = "Agent"): EventSearchFields => ({
+  eventType,
+  message,
+  source,
+});
+
+const timeline: EventSearchFields[] = [
+  ev("app_install_started", "Installing Contoso Reader"),
+  ev("app_install_progress", "Downloading 42%"),
+  ev("app_install_completed", "Contoso Reader installed"),
+  ev("esp_provisioning_status", "DeviceSetup: Apps 3/7"),
+  ev("enrollment_failed", "Apps failed with exit code -1", "DecisionEngine"),
+];
+
+const visible = (query: string) => {
+  const matcher = buildEventSearchMatcher(query);
+  const rows = matcher ? timeline.filter(matcher) : timeline;
+  return rows.map(e => e.eventType);
+};
+
+describe("parseEventSearchQuery", () => {
+  it("splits whitespace-separated terms and lowercases them", () => {
+    expect(parseEventSearchQuery("ESP Provisioning")).toEqual({
+      include: ["esp", "provisioning"],
+      exclude: [],
+    });
+  });
+
+  it("reads a leading minus as an exclusion", () => {
+    expect(parseEventSearchQuery("error -app_install_progress -perf")).toEqual({
+      include: ["error"],
+      exclude: ["app_install_progress", "perf"],
+    });
+  });
+
+  it("keeps a quoted minus literal — otherwise an exit code could not be searched", () => {
+    expect(parseEventSearchQuery('"-1"')).toEqual({ include: ["-1"], exclude: [] });
+  });
+
+  it("excludes a quoted phrase as one term", () => {
+    expect(parseEventSearchQuery('-"exit code 1"')).toEqual({
+      include: [],
+      exclude: ["exit code 1"],
+    });
+  });
+
+  it("drops a lone minus so the timeline does not blank out mid-typing", () => {
+    expect(parseEventSearchQuery("-")).toEqual({ include: [], exclude: [] });
+  });
+
+  it("de-duplicates repeated terms", () => {
+    expect(parseEventSearchQuery("app app -perf -perf")).toEqual({
+      include: ["app"],
+      exclude: ["perf"],
+    });
+  });
+});
+
+describe("buildEventSearchMatcher", () => {
+  it("returns null when there is nothing to filter on", () => {
+    expect(buildEventSearchMatcher("")).toBeNull();
+    expect(buildEventSearchMatcher("   ")).toBeNull();
+    expect(buildEventSearchMatcher("-")).toBeNull();
+  });
+
+  it("matches event type, message and source", () => {
+    const matcher = buildEventSearchMatcher("decisionengine")!;
+    expect(timeline.filter(matcher).map(e => e.eventType)).toEqual(["enrollment_failed"]);
+    expect(visible("contoso")).toEqual(["app_install_started", "app_install_completed"]);
+  });
+
+  it("hides every match of an excluded term", () => {
+    expect(visible("-app_install_progress")).toEqual([
+      "app_install_started",
+      "app_install_completed",
+      "esp_provisioning_status",
+      "enrollment_failed",
+    ]);
+  });
+
+  it("treats a partial type name as a prefix filter over the whole family", () => {
+    expect(visible("-app_install")).toEqual(["esp_provisioning_status", "enrollment_failed"]);
+  });
+
+  it("combines a search term with exclusions", () => {
+    expect(visible("apps -esp")).toEqual(["enrollment_failed"]);
+  });
+
+  it("ANDs multiple search terms across different fields", () => {
+    expect(visible("app_install contoso")).toEqual([
+      "app_install_started",
+      "app_install_completed",
+    ]);
+  });
+
+  it("never matches a term across a field boundary", () => {
+    // "started" ends eventType, "Installing" opens message — a naive concatenation
+    // would let the joined string match.
+    expect(visible("startedinstalling")).toEqual([]);
+  });
+
+  it("is case-insensitive on both sides", () => {
+    expect(visible("-APP_INSTALL_PROGRESS")).not.toContain("app_install_progress");
+  });
+
+  it("lets an exclusion win over a search term that also matches", () => {
+    expect(visible("app_install -progress")).toEqual([
+      "app_install_started",
+      "app_install_completed",
+    ]);
+  });
+});
diff --git a/src/Web/autopilot-monitor-web/app/sessions/utils/eventSearchQuery.ts b/src/Web/autopilot-monitor-web/app/sessions/utils/eventSearchQuery.ts
new file mode 100644
index 00000000..683be4bb
--- /dev/null
+++ b/src/Web/autopilot-monitor-web/app/sessions/utils/eventSearchQuery.ts
@@ -0,0 +1,105 @@
+// Search syntax for the Event Timeline search box.
+//
+// Follows the convention every search box shares (Google, GitHub, Gmail, Jira):
+// whitespace-separated terms are AND-ed, a leading minus turns a term into an
+// exclusion. Both sides match the same fields — eventType, message, source — so
+// `-x` is exactly the negation of searching for `x`, with no second rule to learn.
+//
+//   error                    events matching "error"
+//   esp provisioning         events matching BOTH terms (in any of the three fields)
+//   -app_install_progress    everything EXCEPT matches of that term
+//   error -heartbeat         combined
+//   "-1"                     quoted: a literal minus, not an exclusion
+//   -"exit code 1"           excludes the whole phrase
+//
+// Matching is case-insensitive substring, so a partial type name such as
+// `-app_install` hides every app_install_* event.
+
+/** The fields a search term is matched against. Structural subset of EnrollmentEvent. */
+export interface EventSearchFields {
+  eventType?: string | null;
+  message?: string | null;
+  source?: string | null;
+}
+
+export interface ParsedEventSearchQuery {
+  /** Terms that must all match. Lowercased. */
+  include: string[];
+  /** Terms that must not match. Lowercased. */
+  exclude: string[];
+}
+
+interface Token {
+  text: string;
+  negated: boolean;
+}
+
+// Hand-rolled so a quote can protect a leading minus: the negation is decided at
+// the first character of a token, before any quote is consumed, which makes `"-1"`
+// a literal search term while `-"foo bar"` excludes the phrase.
+function tokenize(query: string): Token[] {
+  const tokens: Token[] = [];
+  let current: Token | null = null;
+  let inQuotes = false;
+
+  const flush = () => {
+    if (current && current.text !== "") tokens.push(current);
+    current = null;
+  };
+
+  for (const ch of query) {
+    if (!inQuotes && /\s/.test(ch)) {
+      flush();
+      continue;
+    }
+    if (ch === '"') {
+      current ??= { text: "", negated: false };
+      inQuotes = !inQuotes;
+      continue;
+    }
+    if (current === null) {
+      // First character of a token: a bare minus opens an exclusion.
+      if (ch === "-") {
+        current = { text: "", negated: true };
+        continue;
+      }
+      current = { text: "", negated: false };
+    }
+    current.text += ch;
+  }
+  flush();
+
+  return tokens;
+}
+
+export function parseEventSearchQuery(query: string): ParsedEventSearchQuery {
+  const include: string[] = [];
+  const exclude: string[] = [];
+
+  for (const token of tokenize(query)) {
+    const text = token.text.toLowerCase();
+    const target = token.negated ? exclude : include;
+    if (!target.includes(text)) target.push(text);
+  }
+
+  return { include, exclude };
+}
+
+/**
+ * Predicate for the parsed query, or null when the query carries no filter at all
+ * (empty, whitespace, or a lone minus while the user is still typing) — callers use
+ * null to skip filtering entirely rather than filtering with an always-true predicate.
+ */
+export function buildEventSearchMatcher(
+  query: string,
+): ((event: EventSearchFields) => boolean) | null {
+  const { include, exclude } = parseEventSearchQuery(query);
+  if (include.length === 0 && exclude.length === 0) return null;
+
+  return (event: EventSearchFields) => {
+    // Newline-joined so a term can never match across a field boundary, while a
+    // multi-term query is still free to satisfy its terms from different fields.
+    const haystack = `${event.eventType ?? ""}\n${event.message ?? ""}\n${event.source ?? ""}`.toLowerCase();
+    return include.every(t => haystack.includes(t)) && !exclude.some(t => haystack.includes(t));
+  };
+}