diff --git a/tools/hygiene/audit-user-scope-memory-index.test.ts b/tools/hygiene/audit-user-scope-memory-index.test.ts
new file mode 100644
index 0000000000..ec3902182e
--- /dev/null
+++ b/tools/hygiene/audit-user-scope-memory-index.test.ts
@@ -0,0 +1,137 @@
+// audit-user-scope-memory-index.test.ts — basic correctness tests for the
+// MEMORY.md bloat auditor. Uses temp files; doesn't touch the real user-scope
+// memory directory.
+
+import { describe, expect, test } from "bun:test";
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { audit, renderReport } from "./audit-user-scope-memory-index.ts";
+
+function withTempMemory(content: string, fn: (path: string) => void): void {
+    const dir = mkdtempSync(join(tmpdir(), "audit-memory-test-"));
+    const path = join(dir, "MEMORY.md");
+    try {
+        writeFileSync(path, content);
+        fn(path);
+    } finally {
+        rmSync(dir, { recursive: true, force: true });
+    }
+}
+
+describe("audit", () => {
+    test("counts a tiny well-formed index correctly", () => {
+        const content = [
+            "# header",
+            "",
+            "- [Title A](a.md) — short hook.",
+            "- [Title B](b.md) — short hook.",
+            "",
+        ].join("\n");
+        withTempMemory(content, (path) => {
+            const r = audit(path);
+            expect(r.totalEntries).toBe(2);
+            expect(r.entriesOverLimit).toBe(0);
+            expect(r.truncationRisk).toBe(false);
+            expect(r.linesPastCutoff).toBe(0);
+        });
+    });
+
+    test("flags over-limit entries", () => {
+        const longHook = "x".repeat(300);
+        const content = [
+            "- [Short Entry](a.md) — fine.",
+            `- [Bloat Entry](b.md) — ${longHook}`,
+        ].join("\n");
+        withTempMemory(content, (path) => {
+            const r = audit(path);
+            expect(r.totalEntries).toBe(2);
+            expect(r.entriesOverLimit).toBe(1);
+            expect(r.bloatEntries).toHaveLength(1);
+            expect(r.bloatEntries[0]!.chars).toBeGreaterThan(200);
+        });
+    });
+
+    test("computes truncation risk when over 200 lines", () => {
+        const lines: string[] = [];
+        for (let i = 0; i < 250; i++) lines.push(`- [Entry ${i}](e${i}.md) — hook.`);
+        const content = lines.join("\n");
+        withTempMemory(content, (path) => {
+            const r = audit(path);
+            expect(r.totalEntries).toBe(250);
+            expect(r.truncationRisk).toBe(true);
+            expect(r.linesPastCutoff).toBeGreaterThan(0);
+        });
+    });
+
+    test("only counts lines starting with `- [` as entries", () => {
+        const content = [
+            "# Heading",
+            "",
+            "Some prose paragraph.",
+            "- [Entry A](a.md) — hook.",
+            "- Just a regular bullet without bracket",
+            "- [Entry B](b.md) — hook.",
+            "",
+        ].join("\n");
+        withTempMemory(content, (path) => {
+            const r = audit(path);
+            expect(r.totalEntries).toBe(2);
+        });
+    });
+
+    test("returns 0 entries for a content-free index", () => {
+        const content = "# MEMORY.md\n\nNo entries yet.\n";
+        withTempMemory(content, (path) => {
+            const r = audit(path);
+            expect(r.totalEntries).toBe(0);
+            expect(r.avgEntryChars).toBe(0);
+        });
+    });
+});
+
+describe("renderReport", () => {
+    test("renders a clean report with no bloat", () => {
+        const fixed = new Date("2026-05-14T00:00:00Z");
+        const md = renderReport(
+            {
+                memoryPath: "/tmp/MEMORY.md",
+                totalLines: 50,
+                totalBytes: 1500,
+                totalEntries: 10,
+                avgEntryChars: 80,
+                entriesOverLimit: 0,
+                bloatEntries: [],
+                linesPastCutoff: 0,
+                truncationRisk: false,
+            },
+            fixed,
+        );
+        expect(md).toContain("Total lines: 50");
+        expect(md).toContain("Truncation risk: no");
+        expect(md).toContain("_None — all entries under the limit._");
+    });
+
+    test("renders the bloat table for over-limit entries", () => {
+        const fixed = new Date("2026-05-14T00:00:00Z");
+        const md = renderReport(
+            {
+                memoryPath: "/tmp/MEMORY.md",
+                totalLines: 300,
+                totalBytes: 70_000,
+                totalEntries: 200,
+                avgEntryChars: 280,
+                entriesOverLimit: 80,
+                bloatEntries: [
+                    { lineNumber: 5, chars: 620, preview: "- [Long entry](a.md) — ..." },
+                ],
+                linesPastCutoff: 100,
+                truncationRisk: true,
+            },
+            fixed,
+        );
+        expect(md).toContain("Truncation risk: YES");
+        expect(md).toContain("Lines past cutoff (truncation risk): 100");
+        expect(md).toContain("| 5 | 620 |");
+    });
+});
diff --git a/tools/hygiene/audit-user-scope-memory-index.ts b/tools/hygiene/audit-user-scope-memory-index.ts
new file mode 100644
index 0000000000..9bf03bc5f2
--- /dev/null
+++ b/tools/hygiene/audit-user-scope-memory-index.ts
@@ -0,0 +1,217 @@
+#!/usr/bin/env bun
+// audit-user-scope-memory-index.ts — detect bloat in the user-scope MEMORY.md.
+//
+// Mechanizes B-0517 Phase 2 (MEMORY.md index audit) — parallel in shape to
+// audit-rule-cross-refs.ts. See B-0517 for the empirical state that prompted
+// this tool: 242 lines / 66KB / 237 entries, ~15% past the cold-boot cutoff,
+// avg entry size 275 chars vs 200-char guidance.
+//
+// What this does:
+//
+//   - Reads the user-scope `~/.claude/projects/<slug>/memory/MEMORY.md` index
+//   - Counts total lines / bytes / entries
+//   - Flags entries exceeding the 200-char guidance
+//   - Computes truncation risk (lines past 200 are silently dropped at fast-path)
+//
+// Out of scope:
+//
+//   Bulk-trim execution — this tool is detect-only. B-0517 Phase 1 is the
+//   one-time bulk cleanup; this Phase 2 tool prevents recurrence by surfacing
+//   the bloat metrics for human / Otto triage.
+//
+// Usage:
+//
+//   bun tools/hygiene/audit-user-scope-memory-index.ts                # detect-only
+//   bun tools/hygiene/audit-user-scope-memory-index.ts --report PATH  # write markdown report
+//   bun tools/hygiene/audit-user-scope-memory-index.ts --memory PATH  # override MEMORY.md location
+//
+// Exit codes:
+//
+//   0   always (detect-only; no enforcement; humans triage bloat)
+//   64  argument error
+//   128 MEMORY.md not found
+//
+// DST-friendliness:
+//
+//   Read-only audit. The "Generated" timestamp in markdown reports is the
+//   only non-deterministic surface. Per `typescript.md` universal-DST gate.
+
+import { existsSync, readFileSync, writeFileSync } from "node:fs";
+import { homedir } from "node:os";
+import { join } from "node:path";
+
+const COLD_BOOT_CUTOFF_LINES = 200;
+const ENTRY_LENGTH_LIMIT_CHARS = 200;
+
+type AuditExitCode = 0 | 64 | 128;
+
+interface Args {
+    readonly report: string | null;
+    readonly memoryPath: string | null;
+}
+
+interface BloatEntry {
+    readonly lineNumber: number;
+    readonly chars: number;
+    readonly preview: string;
+}
+
+interface AuditResult {
+    readonly memoryPath: string;
+    readonly totalLines: number;
+    readonly totalBytes: number;
+    readonly totalEntries: number;
+    readonly avgEntryChars: number;
+    readonly entriesOverLimit: number;
+    readonly bloatEntries: BloatEntry[]; // top 10 by char count
+    readonly linesPastCutoff: number;
+    readonly truncationRisk: boolean;
+}
+
+function defaultMemoryPath(): string {
+    const home = process.env.HOME ?? homedir();
+    return join(home, ".claude/projects/-Users-acehack-Documents-src-repos-Zeta/memory/MEMORY.md");
+}
+
+function parseArgs(argv: string[]): { kind: "args"; args: Args } | { kind: "error"; message: string } {
+    let report: string | null = null;
+    let memoryPath: string | null = null;
+    let i = 0;
+    while (i < argv.length) {
+        const a = argv[i]!;
+        if (a === "--report") {
+            const next = argv[i + 1];
+            if (!next) return { kind: "error", message: "--report requires a path" };
+            report = next;
+            i += 2;
+        } else if (a === "--memory") {
+            const next = argv[i + 1];
+            if (!next) return { kind: "error", message: "--memory requires a path" };
+            memoryPath = next;
+            i += 2;
+        } else {
+            return { kind: "error", message: `Unknown argument: ${a}` };
+        }
+    }
+    return { kind: "args", args: { report, memoryPath } };
+}
+
+function audit(memoryPath: string): AuditResult {
+    const content = readFileSync(memoryPath, "utf8");
+    const lines = content.split("\n");
+    const totalLines = lines.length;
+    const totalBytes = Buffer.byteLength(content, "utf8");
+
+    const bloat: BloatEntry[] = [];
+    let entryCount = 0;
+    let entryCharsTotal = 0;
+    let overLimitCount = 0;
+
+    for (let i = 0; i < lines.length; i++) {
+        const line = lines[i]!;
+        if (!line.startsWith("- [")) continue;
+        entryCount++;
+        const chars = line.length;
+        entryCharsTotal += chars;
+        if (chars > ENTRY_LENGTH_LIMIT_CHARS) {
+            overLimitCount++;
+            bloat.push({
+                lineNumber: i + 1,
+                chars,
+                preview: line.slice(0, 100),
+            });
+        }
+    }
+
+    const top10 = bloat.sort((a, b) => b.chars - a.chars).slice(0, 10);
+    const linesPastCutoff = Math.max(0, totalLines - COLD_BOOT_CUTOFF_LINES);
+
+    return {
+        memoryPath,
+        totalLines,
+        totalBytes,
+        totalEntries: entryCount,
+        avgEntryChars: entryCount === 0 ? 0 : Math.round(entryCharsTotal / entryCount),
+        entriesOverLimit: overLimitCount,
+        bloatEntries: top10,
+        linesPastCutoff,
+        truncationRisk: totalLines > COLD_BOOT_CUTOFF_LINES,
+    };
+}
+
+function renderReport(result: AuditResult, now: Date): string {
+    const lines: string[] = [];
+    lines.push("# user-scope MEMORY.md bloat audit");
+    lines.push("");
+    lines.push(`Generated: ${now.toISOString()}`);
+    lines.push(`Source: \`${result.memoryPath}\``);
+    lines.push("");
+    lines.push("## Summary");
+    lines.push("");
+    lines.push(`- Total lines: ${result.totalLines}`);
+    lines.push(`- Total bytes: ${result.totalBytes.toLocaleString()}`);
+    lines.push(`- Total entries: ${result.totalEntries}`);
+    lines.push(`- Average entry size: ${result.avgEntryChars} chars`);
+    lines.push(`- Entries over ${ENTRY_LENGTH_LIMIT_CHARS} chars: ${result.entriesOverLimit}`);
+    lines.push(`- Cold-boot cutoff: line ${COLD_BOOT_CUTOFF_LINES}`);
+    lines.push(`- Lines past cutoff (truncation risk): ${result.linesPastCutoff}`);
+    lines.push(`- Truncation risk: ${result.truncationRisk ? "YES" : "no"}`);
+    lines.push("");
+    if (result.bloatEntries.length === 0) {
+        lines.push("## Top bloat entries");
+        lines.push("");
+        lines.push("_None — all entries under the limit._");
+    } else {
+        lines.push("## Top 10 bloat entries (sorted by char count)");
+        lines.push("");
+        lines.push("| Line | Chars | Preview |");
+        lines.push("|------|-------|---------|");
+        for (const e of result.bloatEntries) {
+            const preview = e.preview.replace(/\|/g, "\\|");
+            lines.push(`| ${e.lineNumber} | ${e.chars} | ${preview}... |`);
+        }
+    }
+    lines.push("");
+    lines.push("## Cleanup procedure");
+    lines.push("");
+    lines.push("Per B-0517 Phase 1: for each over-limit entry,");
+    lines.push("");
+    lines.push("1. Read the underlying topic file (`memory/<filename>`)");
+    lines.push("2. Verify the topic file's body + frontmatter `description:` contain the full detail");
+    lines.push("3. Rewrite the MEMORY.md entry to a short hook (~50-100 chars):");
+    lines.push("   `- [Short Title](filename.md) — one-line hook.`");
+    lines.push("");
+    return lines.join("\n");
+}
+
+function main(argv: string[]): AuditExitCode {
+    const parsed = parseArgs(argv);
+    if (parsed.kind === "error") {
+        console.error(`error: ${parsed.message}`);
+        return 64;
+    }
+
+    const memoryPath = parsed.args.memoryPath ?? defaultMemoryPath();
+    if (!existsSync(memoryPath)) {
+        console.error(`MEMORY.md not found at ${memoryPath}`);
+        return 128;
+    }
+
+    const result = audit(memoryPath);
+    const report = renderReport(result, new Date());
+
+    if (parsed.args.report) {
+        writeFileSync(parsed.args.report, report);
+        console.log(`wrote ${parsed.args.report}`);
+    } else {
+        console.log(report);
+    }
+
+    return 0;
+}
+
+if (import.meta.main) {
+    process.exit(main(process.argv.slice(2)));
+}
+
+export { audit, renderReport };