diff --git a/packages/tooling/vis/__tests__/security/multi-eco-lockfiles.fuzz.test.ts b/packages/tooling/vis/__tests__/security/multi-eco-lockfiles.fuzz.test.ts
new file mode 100644
index 00000000..7f9fa918
--- /dev/null
+++ b/packages/tooling/vis/__tests__/security/multi-eco-lockfiles.fuzz.test.ts
@@ -0,0 +1,150 @@
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { afterAll, beforeAll, describe, expect, it } from "vitest";
+
+import { lockedPackagesForEcosystem } from "../../src/security/multi-eco-lockfiles";
+
+const ITERATIONS = 300;
+const RNG_SEED = 1337;
+
+// Deterministic Lehmer generator (MINSTD). Products stay below 2^53, so the sequence keeps its full period.
+// A failing iteration replays from RNG_SEED and its index.
+const createRandom = (seed: number): (() => number) => {
+    let state = seed;
+
+    return (): number => {
+        state = (state * 48_271) % 2_147_483_647;
+
+        return state / 2_147_483_647;
+    };
+};
+
+/* eslint-disable @stylistic/quotes -- sample lockfiles embed double quotes; prettier picks single quotes to avoid escapes */
+const SAMPLES: Record<string, { ecosystem: string; sample: string }> = {
+    "Cargo.lock": {
+        ecosystem: "cargo",
+        sample: '[[package]]\nname = "serde"\nversion = "1.0.0"\n\n[[package]]\nname = "tokio"\nversion = "1.38.0"\n',
+    },
+    "composer.lock": {
+        ecosystem: "composer",
+        sample: '{"packages":[{"name":"a/b","version":"1.0.0"}],"packages-dev":[{"name":"c/d","version":"2.0.0"}]}',
+    },
+    "Gemfile.lock": {
+        ecosystem: "rubygems",
+        sample: "GEM\n  remote: https://rubygems.org/\n  specs:\n    rake (13.0.1)\n\nPLATFORMS\n  ruby\n",
+    },
+    "go.sum": {
+        ecosystem: "go",
+        sample: "github.com/a/b v1.2.3 h1:abc=\ngithub.com/a/b v1.2.3/go.mod h1:def=\n",
+    },
+    "gradle.lockfile": {
+        ecosystem: "maven",
+        sample: "# Generated by Gradle\norg.example:lib:1.2.3=compileClasspath,runtimeClasspath\nempty=annotationProcessor\n",
+    },
+    "mix.lock": {
+        ecosystem: "hex",
+        sample: '%{\n  "jason": {:hex, :jason, "1.4.0", "hash", [:mix], [], "hexpm", "x"},\n}\n',
+    },
+    "Package.resolved": {
+        ecosystem: "swift",
+        sample: '{"pins":[{"identity":"a","location":"https://example.com/a.git","state":{"version":"1.0.0"}}],"version":2}',
+    },
+    "packages.lock.json": {
+        ecosystem: "nuget",
+        sample: '{"version":1,"dependencies":{"net8.0":{"Newtonsoft.Json":{"type":"Direct","resolved":"13.0.1"}}}}',
+    },
+    "Pipfile.lock": {
+        ecosystem: "pypi",
+        sample: '{"default":{"requests":{"version":"==2.31.0"}},"develop":{"pytest":{"version":"==8.0.0"}}}',
+    },
+    "pom.xml": {
+        ecosystem: "maven",
+        sample: "<project><modelVersion>4.0.0</modelVersion><groupId>g</groupId><artifactId>a</artifactId><version>1</version><dependencies><dependency><groupId>org.x</groupId><artifactId>lib</artifactId><version>1.2.3</version></dependency></dependencies></project>",
+    },
+    "pubspec.lock": {
+        ecosystem: "pub",
+        sample: 'packages:\n  path:\n    dependency: "direct main"\n    source: hosted\n    version: "1.8.0"\nsdks:\n  dart: ">=3.0.0 <4.0.0"\n',
+    },
+    "uv.lock": {
+        ecosystem: "pypi",
+        sample: '[[package]]\nname = "requests"\nversion = "2.31.0"\n',
+    },
+};
+
+/* eslint-enable @stylistic/quotes */
+
+const ALPHABET = `{}[]()"'\\:,=#%\n\r\t -./0123456789abcdefghijklmnopqrstuvwxyz\u0000\uFFFD`;
+
+// Mutates a valid sample: a few deletes and inserts with a rare truncation, or pure noise about one time in ten.
+// Truncation stays rare because a truncated JSON sample fails at parse time and never reaches the post-parse code.
+const mutate = (sample: string, random: () => number): string => {
+    if (random() < 0.1) {
+        return Array.from({ length: Math.floor(random() * 256) }, () => String.fromCodePoint(Math.floor(random() * 2048))).join("");
+    }
+
+    let out = sample;
+    const ops = 1 + Math.floor(random() * 4);
+
+    for (let i = 0; i < ops; i++) {
+        const position = Math.floor(random() * (out.length + 1));
+        const kind = random();
+
+        if (kind < 0.475) {
+            out = out.slice(0, position) + out.slice(position + 1);
+        } else if (kind < 0.95) {
+            out = out.slice(0, position) + ALPHABET.charAt(Math.floor(random() * ALPHABET.length)) + out.slice(position);
+        } else {
+            out = out.slice(0, position);
+        }
+    }
+
+    return out;
+};
+
+describe(lockedPackagesForEcosystem, () => {
+    let root: string;
+
+    beforeAll(() => {
+        root = mkdtempSync(join(tmpdir(), "vis-lockfile-fuzz-"));
+    });
+
+    afterAll(() => {
+        rmSync(root, { force: true, recursive: true });
+    });
+
+    it.each(Object.entries(SAMPLES))("parses the %s sample and survives mutated inputs without throwing", (file, { ecosystem, sample }) => {
+        expect.assertions(2);
+
+        const dir = mkdtempSync(join(root, "case-"));
+
+        // Guard against a sample that silently stops parsing, which would make the fuzz loop vacuous.
+        writeFileSync(join(dir, file), sample);
+
+        expect(lockedPackagesForEcosystem(dir, ecosystem).length).toBeGreaterThan(0);
+
+        const random = createRandom(RNG_SEED);
+        const failures: string[] = [];
+
+        for (let i = 0; i < ITERATIONS; i++) {
+            const input = mutate(sample, random);
+
+            writeFileSync(join(dir, file), input);
+
+            try {
+                const packages = lockedPackagesForEcosystem(dir, ecosystem);
+
+                if (
+                    !packages.every((pkg) => typeof pkg.name === "string" && typeof pkg.version === "string" && pkg.name.length > 0 && pkg.version.length > 0)
+                ) {
+                    failures.push(`iteration ${i}: malformed entry for input ${JSON.stringify(input)}`);
+                }
+            } catch (error) {
+                failures.push(`iteration ${i}: ${String(error)} for input ${JSON.stringify(input)}`);
+            }
+        }
+
+        expect({ count: failures.length, first: failures.slice(0, 5) }).toStrictEqual({ count: 0, first: [] });
+    });
+});