diff --git a/.cspell.json b/.cspell.json
index cfc24d9..1c3e15e 100644
--- a/.cspell.json
+++ b/.cspell.json
@@ -14,6 +14,7 @@
     "eslint-plugin",
     "parser",
     "cspell",
+    "dry-aged-deps",
     "eslint-config-prettier",
     "eslint-import-resolver-node",
     "eslint-import-resolver-typescript",
@@ -90,6 +91,7 @@
   ],
   "ignorePaths": [
     "docs",
+    ".dry-aged-deps.json",
     ".eslintignore",
     ".eslintrc-json.json",
     ".eslintrc.json",
@@ -101,7 +103,6 @@
     ".github/workflows/release.yml",
     ".github/workflows/upgrade-main.yml",
     ".gitignore",
-    ".mergify.yml",
     ".npmignore",
     ".prettierignore",
     ".prettierrc.json",
diff --git a/.dry-aged-deps.json b/.dry-aged-deps.json
new file mode 100644
index 0000000..ae79709
--- /dev/null
+++ b/.dry-aged-deps.json
@@ -0,0 +1,24 @@
+{
+  "exclude": {
+    "@types/jest": "Pinned to jest 27.x; upgrade requires jest 29+ migration",
+    "cspell": "Major version upgrade; requires compatibility testing with current config",
+    "eslint": "Pinned to ^8; upgrade to 9+ requires flat config migration and plugin compatibility",
+    "eslint-config-prettier": "Major version upgrade; blocked by eslint 8.x constraint",
+    "eslint-import-resolver-node": "Pinned by eslint-plugin-import compatibility",
+    "eslint-import-resolver-typescript": "Major version upgrade; blocked by eslint 8.x constraint",
+    "eslint-plugin-import": "Pinned by eslint 8.x compatibility",
+    "eslint-plugin-no-secrets": "Major version upgrade; blocked by eslint 8.x constraint",
+    "eslint-plugin-prettier": "Major version upgrade; blocked by eslint 8.x constraint",
+    "eslint-plugin-unicorn": "Major version upgrade; blocked by eslint 8.x constraint",
+    "http-status-codes": "Used only in tests; minor update with no security impact",
+    "husky": "Major version upgrade; requires migration to new config format",
+    "jest": "Pinned to ^27 by projen; upgrade requires projen and ts-jest migration",
+    "jest-junit": "Major version upgrade; blocked by jest 27.x constraint",
+    "npm-check-updates": "Major version upgrade; used only for maintenance scripts",
+    "prettier": "Major version upgrade; may cause formatting changes across codebase",
+    "projen": "Pinned to ^0.58; upgrade may cause breaking changes to project config",
+    "ts-jest": "Pinned to jest 27.x; upgrade requires jest migration",
+    "ts-node": "Minor update; low priority with no security impact",
+    "typescript": "Major version upgrade; requires codebase compatibility verification"
+  }
+}
diff --git a/.eslintignore b/.eslintignore
index 2dc2f32..4ad7ddf 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -15,7 +15,6 @@
 .husky/commit-msg
 .husky/pre-commit
 .husky/pre-push
-.mergify.yml
 .npmignore
 .prettierignore
 .prettierrc.json
diff --git a/.eslintrc.json b/.eslintrc.json
index a2e833e..0b7eba6 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -208,7 +208,6 @@
         ".github/workflows/release.yml",
         ".github/workflows/upgrade-main.yml",
         ".gitignore",
-        ".mergify.yml",
         ".npmignore",
         ".prettierignore",
         ".prettierrc.json",
diff --git a/.gitattributes b/.gitattributes
index ee0304a..1f3b110 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -17,7 +17,6 @@
 /.husky/commit-msg linguist-generated
 /.husky/pre-commit linguist-generated
 /.husky/pre-push linguist-generated
-/.mergify.yml linguist-generated
 /.npmignore linguist-generated
 /.prettierignore linguist-generated
 /.prettierrc.json linguist-generated
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 03d6f68..33c0f94 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -15,7 +15,7 @@ jobs:
       CI: "true"
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.ref }}
           repository: ${{ github.event.pull_request.head.repo.full_name }}
@@ -23,6 +23,8 @@ jobs:
         run: yarn install --check-files
       - name: build
         run: npx projen build
+      - name: Check for outdated dependencies
+        run: npx dry-aged-deps --check
       - id: self_mutation
         name: Find mutations
         run: |-
@@ -30,7 +32,7 @@ jobs:
           git diff --staged --patch --exit-code > .repo.patch || echo "::set-output name=self_mutation_happened::true"
       - if: steps.self_mutation.outputs.self_mutation_happened
         name: Upload patch
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: .repo.patch
           path: .repo.patch
@@ -48,13 +50,13 @@ jobs:
     if: always() && needs.build.outputs.self_mutation_happened && !(github.event.pull_request.head.repo.full_name != github.repository)
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           token: ${{ secrets.PROJEN_GITHUB_TOKEN }}
           ref: ${{ github.event.pull_request.head.ref }}
           repository: ${{ github.event.pull_request.head.repo.full_name }}
       - name: Download patch
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: .repo.patch
           path: ${{ runner.temp }}
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 802ca24..3bd09cd 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -17,7 +17,7 @@ jobs:
       CI: "true"
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Set git identity
@@ -33,7 +33,7 @@ jobs:
         run: echo ::set-output name=latest_commit::"$(git ls-remote origin -h ${{ github.ref }} | cut -f1)"
       - name: Upload artifact
         if: ${{ steps.git_remote.outputs.latest_commit == github.sha }}
-        uses: actions/upload-artifact@v2.1.1
+        uses: actions/upload-artifact@v4
         with:
           name: build-artifact
           path: dist
@@ -45,11 +45,11 @@ jobs:
       contents: write
     if: needs.release.outputs.latest_commit == github.sha
     steps:
-      - uses: actions/setup-node@v3
+      - uses: actions/setup-node@v4
         with:
           node-version: 14.x
       - name: Download build artifacts
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: build-artifact
           path: dist
@@ -67,11 +67,11 @@ jobs:
       contents: read
     if: needs.release.outputs.latest_commit == github.sha
     steps:
-      - uses: actions/setup-node@v3
+      - uses: actions/setup-node@v4
         with:
           node-version: 14.x
       - name: Download build artifacts
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: build-artifact
           path: dist
diff --git a/.github/workflows/upgrade-main.yml b/.github/workflows/upgrade-main.yml
index af1c1cd..5bed630 100644
--- a/.github/workflows/upgrade-main.yml
+++ b/.github/workflows/upgrade-main.yml
@@ -15,7 +15,7 @@ jobs:
       patch_created: ${{ steps.create_patch.outputs.patch_created }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: main
       - name: Install dependencies
@@ -29,7 +29,7 @@ jobs:
           git diff --staged --patch --exit-code > .repo.patch || echo "::set-output name=patch_created::true"
       - if: steps.create_patch.outputs.patch_created
         name: Upload patch
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: .repo.patch
           path: .repo.patch
@@ -43,12 +43,12 @@ jobs:
     if: ${{ needs.upgrade.outputs.patch_created }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           token: ${{ secrets.PROJEN_GITHUB_TOKEN }}
           ref: main
       - name: Download patch
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: .repo.patch
           path: ${{ runner.temp }}
diff --git a/.gitignore b/.gitignore
index 73779e3..78d268d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -39,7 +39,6 @@ junit.xml
 /dist/changelog.md
 /dist/version.txt
 !/.github/workflows/release.yml
-!/.mergify.yml
 !/.github/workflows/upgrade-main.yml
 !/.github/pull_request_template.md
 !/.prettierignore
diff --git a/.husky/pre-push b/.husky/pre-push
index f3e5d85..82f2bab 100755
--- a/.husky/pre-push
+++ b/.husky/pre-push
@@ -1,4 +1,5 @@
 #!/bin/sh
 . "$(dirname "$0")/_/husky.sh"
 npm run test
-npm run eslint
\ No newline at end of file
+npm run eslint
+npx dry-aged-deps --check
\ No newline at end of file
diff --git a/.mergify.yml b/.mergify.yml
deleted file mode 100644
index eddac7d..0000000
--- a/.mergify.yml
+++ /dev/null
@@ -1,23 +0,0 @@
-# ~~ Generated by projen. To modify, edit .projenrc.js and run "npx projen".
-
-queue_rules:
-  - name: default
-    conditions:
-      - "#approved-reviews-by>=1"
-      - -label~=(do-not-merge)
-      - status-success=build
-pull_request_rules:
-  - name: Automatic merge on approval and successful build
-    actions:
-      delete_head_branch: {}
-      queue:
-        method: squash
-        name: default
-        commit_message_template: |-
-          {{ title }} (#{{ number }})
-
-          {{ body }}
-    conditions:
-      - "#approved-reviews-by>=1"
-      - -label~=(do-not-merge)
-      - status-success=build
diff --git a/.npmignore b/.npmignore
index 77227ac..ad0995b 100644
--- a/.npmignore
+++ b/.npmignore
@@ -5,7 +5,6 @@ junit.xml
 /coverage/
 /dist/changelog.md
 /dist/version.txt
-/.mergify.yml
 /test/
 /tsconfig.dev.json
 /src/
diff --git a/.project-words.txt b/.project-words.txt
index f7db663..d9e7a4e 100644
--- a/.project-words.txt
+++ b/.project-words.txt
@@ -1,2 +1,4 @@
 Hubber
 deps
+mergify
+yarnrc
diff --git a/.projen/deps.json b/.projen/deps.json
index b7f7044..9d103f5 100644
--- a/.projen/deps.json
+++ b/.projen/deps.json
@@ -39,6 +39,10 @@
       "name": "cspell",
       "type": "build"
     },
+    {
+      "name": "dry-aged-deps",
+      "type": "build"
+    },
     {
       "name": "eslint-config-prettier",
       "type": "build"
diff --git a/.projen/files.json b/.projen/files.json
index 9210305..259ecd7 100644
--- a/.projen/files.json
+++ b/.projen/files.json
@@ -16,7 +16,6 @@
     ".husky/commit-msg",
     ".husky/pre-commit",
     ".husky/pre-push",
-    ".mergify.yml",
     ".npmignore",
     ".prettierignore",
     ".prettierrc.json",
diff --git a/.projen/tasks.json b/.projen/tasks.json
index 1c10b22..f3dc807 100644
--- a/.projen/tasks.json
+++ b/.projen/tasks.json
@@ -129,7 +129,7 @@
           "exec": "mkdir -p dist/js"
         },
         {
-          "exec": "mv $(npm pack) dist/js/"
+          "exec": "npm pack --pack-destination dist/js"
         }
       ]
     },
diff --git a/.projenrc.ts b/.projenrc.ts
index a6dec21..db04894 100644
--- a/.projenrc.ts
+++ b/.projenrc.ts
@@ -39,6 +39,7 @@ const project = new TypeScriptProject({
     "http-status-codes",
     "@types/http-status-codes",
     "@mountainpass/cool-bits-for-projen",
+    "dry-aged-deps",
   ] /* Build dependencies for this module. */,
   keywords: ["problem-details", "rfc7807"],
   defaultReleaseBranch: "main",
@@ -63,6 +64,7 @@ const project = new TypeScriptProject({
     secret: "GITHUB_TOKEN",
   },
   githubOptions: {
+    mergify: false,
     pullRequestLintOptions: {
       semanticTitleOptions: {
         types: [
@@ -83,12 +85,99 @@ const project = new TypeScriptProject({
   },
 });
 
-new Recommended(project, {
-  cSpellOptions: { language: "en-GB", ignorePaths: ["docs"] },
+const recommended = new Recommended(project, {
+  cSpellOptions: {
+    language: "en-GB",
+    ignorePaths: ["docs", ".dry-aged-deps.json"],
+  },
 });
 
+// Add dry-aged-deps check to the pre-push hook
+recommended.husky.addHook("pre-push", "npx dry-aged-deps --check");
+
 new CodeOfConduct(project, { contactMethod: "tom@mountain-pass.com.au" });
 
+// Fix npm pack command for newer npm versions
+const packageTask = project.tasks.tryFind("package")!;
+packageTask.reset();
+packageTask.exec("mkdir -p dist/js");
+packageTask.exec("npm pack --pack-destination dist/js");
+
+// Add dry-aged-deps check to the build workflow
+project.buildWorkflow?.addPostBuildSteps({
+  name: "Check for outdated dependencies",
+  run: "npx dry-aged-deps --check",
+});
+
+// Upgrade deprecated GitHub Actions from v2/v3 to v4
+const buildWorkflow = project.github?.tryFindWorkflow("build");
+if (buildWorkflow?.file) {
+  buildWorkflow.file.addOverride(
+    "jobs.build.steps.0.uses",
+    "actions/checkout@v4"
+  );
+  buildWorkflow.file.addOverride(
+    "jobs.build.steps.5.uses",
+    "actions/upload-artifact@v4"
+  );
+  buildWorkflow.file.addOverride(
+    "jobs.self-mutation.steps.0.uses",
+    "actions/checkout@v4"
+  );
+  buildWorkflow.file.addOverride(
+    "jobs.self-mutation.steps.1.uses",
+    "actions/download-artifact@v4"
+  );
+}
+
+const releaseWorkflow = project.github?.tryFindWorkflow("release");
+if (releaseWorkflow?.file) {
+  releaseWorkflow.file.addOverride(
+    "jobs.release.steps.0.uses",
+    "actions/checkout@v4"
+  );
+  releaseWorkflow.file.addOverride(
+    "jobs.release.steps.5.uses",
+    "actions/upload-artifact@v4"
+  );
+  releaseWorkflow.file.addOverride(
+    "jobs.release_github.steps.0.uses",
+    "actions/setup-node@v4"
+  );
+  releaseWorkflow.file.addOverride(
+    "jobs.release_github.steps.1.uses",
+    "actions/download-artifact@v4"
+  );
+  releaseWorkflow.file.addOverride(
+    "jobs.release_npm.steps.0.uses",
+    "actions/setup-node@v4"
+  );
+  releaseWorkflow.file.addOverride(
+    "jobs.release_npm.steps.1.uses",
+    "actions/download-artifact@v4"
+  );
+}
+
+const upgradeWorkflow = project.github?.tryFindWorkflow("upgrade-main");
+if (upgradeWorkflow?.file) {
+  upgradeWorkflow.file.addOverride(
+    "jobs.upgrade.steps.0.uses",
+    "actions/checkout@v4"
+  );
+  upgradeWorkflow.file.addOverride(
+    "jobs.upgrade.steps.4.uses",
+    "actions/upload-artifact@v4"
+  );
+  upgradeWorkflow.file.addOverride(
+    "jobs.pr.steps.0.uses",
+    "actions/checkout@v4"
+  );
+  upgradeWorkflow.file.addOverride(
+    "jobs.pr.steps.1.uses",
+    "actions/download-artifact@v4"
+  );
+}
+
 gitHubber.addToProject(project);
 npmReleaser.addToProject(project);
 organisational.addToProject(project);
diff --git a/.yarnrc b/.yarnrc
new file mode 100644
index 0000000..4f14322
--- /dev/null
+++ b/.yarnrc
@@ -0,0 +1 @@
+--ignore-engines true
diff --git a/package.json b/package.json
index e4d8610..37c8cfe 100644
--- a/package.json
+++ b/package.json
@@ -45,6 +45,7 @@
     "@typescript-eslint/eslint-plugin": "^5",
     "@typescript-eslint/parser": "^5",
     "cspell": "*",
+    "dry-aged-deps": "^2.6.0",
     "eslint": "^8",
     "eslint-config-prettier": "^8.5.0",
     "eslint-import-resolver-node": "^0.3.6",
@@ -132,6 +133,7 @@
   },
   "types": "lib/index.d.ts",
   "contributors": [
+    "Claude <noreply@anthropic.com>",
     "Tom Howard <tom@windyroad.com.au>",
     "dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>"
   ],
diff --git a/yarn.lock b/yarn.lock
index 4a37d87..a03aa8d 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2449,6 +2449,11 @@ dotgitignore@^2.1.0:
     find-up "^3.0.0"
     minimatch "^3.0.4"
 
+dry-aged-deps@^2.6.0:
+  version "2.6.0"
+  resolved "https://registry.yarnpkg.com/dry-aged-deps/-/dry-aged-deps-2.6.0.tgz#d011e791bdc3b795f95660716ab2c65b8ca39246"
+  integrity sha512-neznE/c94RF2yOV7O3UXbXEL0Ohp6IX8T73h4t03+keCYXLmRIT/yhjGZh8IIvL75JN+HDyOoQQGvIIEvU4GSg==
+
 duplexer3@^0.1.4:
   version "0.1.4"
   resolved "https://registry.yarnpkg.com/duplexer3/-/duplexer3-0.1.4.tgz#ee01dd1cac0ed3cbc7fdbea37dc0a8f1ce002ce2"