diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index bd1522f..a7add3a 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -20,14 +20,14 @@ The extension has no activation code. Changes to a snippet catalog take effect t
 
 ## Commands
 
-There are no npm scripts, automated tests, or lint configuration. The PR workflow mirrors these local validation commands:
+There is no lint configuration. The PR workflow mirrors these local validation commands:
 
 ```bash
 # Install the locked packaging dependency
 npm ci
 
-# Validate all snippet catalogs parse as JSON
-node -e "for (const f of ['snippets/snippets.json','snippets/jinja-snippets.json','snippets/django-snippets.json']) JSON.parse(require('fs').readFileSync(f, 'utf8'))"
+# Validate snippet catalogs and snippet metadata rules
+npm test
 
 # Build a VSIX package (also validates the extension manifest)
 npx vsce package
@@ -37,7 +37,7 @@ npx vsce package
 
 ## Pull request checks
 
-PRs should keep the snippet catalogs parseable and the package manifest valid. The CI workflow runs `npm ci`, JSON parsing for all three snippet catalogs, and `npx vsce package` on every pull request.
+PRs should keep snippet catalogs and metadata valid, and the package manifest valid. The CI workflow runs `npm ci`, `npm test`, and `npx vsce package` on every pull request.
 
 ## Releases
 
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 90f8b20..23b0812 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -21,7 +21,7 @@ jobs:
         run: npm ci
 
       - name: Validate snippet catalogs
-        run: node -e "for (const f of ['snippets/snippets.json','snippets/jinja-snippets.json','snippets/django-snippets.json']) JSON.parse(require('fs').readFileSync(f, 'utf8'))"
+        run: npm test
 
       - name: Package extension
         run: npx vsce package
diff --git a/README.md b/README.md
index 3d39230..d878e46 100644
--- a/README.md
+++ b/README.md
@@ -176,7 +176,7 @@ Found a bug? Want a new snippet? Contributions are welcome!
 Every pull request runs a small validation suite on Node.js 20:
 
 1. `npm ci`
-2. Parse all snippet catalogs as JSON
+2. `npm test` (JSON + snippet metadata validation)
 3. `npx vsce package`
 
 If you want to mirror CI locally before opening a PR, run the same commands from the repository root.
diff --git a/package.json b/package.json
index 5f6b4c3..e91413f 100644
--- a/package.json
+++ b/package.json
@@ -56,6 +56,9 @@
         "url": "https://github.com/EndlessTrax/python-template-snippets"
     },
     "homepage": "https://github.com/EndlessTrax/python-template-snippets/blob/master/README.md",
+    "scripts": {
+        "test": "node scripts/validate-snippets.js"
+    },
     "devDependencies": {
         "@vscode/vsce": "^3.9.2"
     }
diff --git a/scripts/validate-snippets.js b/scripts/validate-snippets.js
new file mode 100644
index 0000000..a2ae8fd
--- /dev/null
+++ b/scripts/validate-snippets.js
@@ -0,0 +1,115 @@
+const fs = require("fs");
+const path = require("path");
+
+const catalogs = [
+    {
+        path: "snippets/snippets.json",
+        label: "shared",
+        expectedPrefix: "pt* (excluding ptj-*/ptd-*)",
+        prefixValidator: (prefix) =>
+            prefix.startsWith("pt") &&
+            !prefix.startsWith("ptj-") &&
+            !prefix.startsWith("ptd-"),
+    },
+    {
+        path: "snippets/jinja-snippets.json",
+        label: "jinja",
+        expectedPrefix: "ptj-*",
+        prefixValidator: (prefix) => prefix.startsWith("ptj-"),
+    },
+    {
+        path: "snippets/django-snippets.json",
+        label: "django",
+        expectedPrefix: "ptd-*",
+        prefixValidator: (prefix) => prefix.startsWith("ptd-"),
+    },
+];
+
+const errors = [];
+const seenPrefixes = new Map();
+
+function addError(message) {
+    errors.push(message);
+}
+
+function validateRequiredString(snippet, fieldName) {
+    return typeof snippet[fieldName] === "string" && snippet[fieldName].trim().length > 0;
+}
+
+for (const catalog of catalogs) {
+    const absolutePath = path.resolve(catalog.path);
+    let parsedCatalog;
+
+    try {
+        const rawCatalog = fs.readFileSync(absolutePath, "utf8");
+        parsedCatalog = JSON.parse(rawCatalog);
+    } catch (error) {
+        if (error && error.code) {
+            addError(`${catalog.path}: failed to read file (${error.message})`);
+        } else {
+            addError(`${catalog.path}: invalid JSON (${error.message})`);
+        }
+        continue;
+    }
+
+    if (
+        parsedCatalog === null ||
+        typeof parsedCatalog !== "object" ||
+        Array.isArray(parsedCatalog)
+    ) {
+        addError(`${catalog.path}: root must be a JSON object keyed by snippet name`);
+        continue;
+    }
+
+    for (const [snippetName, snippet] of Object.entries(parsedCatalog)) {
+        if (snippet === null || typeof snippet !== "object" || Array.isArray(snippet)) {
+            addError(`${catalog.path} > "${snippetName}": snippet definition must be an object`);
+            continue;
+        }
+
+        if (!validateRequiredString(snippet, "prefix")) {
+            addError(`${catalog.path} > "${snippetName}": missing or invalid "prefix"`);
+            continue;
+        }
+
+        const prefix = snippet.prefix;
+
+        if (!Array.isArray(snippet.body) || snippet.body.length === 0) {
+            addError(`${catalog.path} > "${snippetName}": missing or invalid "body" (must be a non-empty array)`);
+        } else if (!snippet.body.every((line) => typeof line === "string")) {
+            addError(`${catalog.path} > "${snippetName}": invalid "body" (all entries must be strings)`);
+        }
+
+        if (!validateRequiredString(snippet, "description")) {
+            addError(`${catalog.path} > "${snippetName}": missing or invalid "description"`);
+        }
+
+        if (!catalog.prefixValidator(prefix)) {
+            addError(
+                `${catalog.path} > "${snippetName}": invalid prefix "${prefix}" for ${catalog.label} catalog (expected ${catalog.expectedPrefix})`
+            );
+        }
+
+        const existing = seenPrefixes.get(prefix);
+        if (existing) {
+            addError(
+                `duplicate prefix "${prefix}" found in ${catalog.path} > "${snippetName}" and ${existing.catalogPath} > "${existing.snippetName}"`
+            );
+        } else {
+            seenPrefixes.set(prefix, {
+                catalogPath: catalog.path,
+                snippetName,
+            });
+        }
+    }
+}
+
+if (errors.length > 0) {
+    console.error("Snippet validation failed:\n");
+    errors.forEach((error, index) => {
+        console.error(`${index + 1}. ${error}`);
+    });
+    process.exit(1);
+}
+
+console.log(`Snippet validation passed (${catalogs.length} catalogs, ${seenPrefixes.size} prefixes checked).`);