diff --git a/.dockerignore b/.dockerignore
index 4efd730c1..ad1631bd8 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -136,6 +136,7 @@ src/
 .pm2.config.js
 .prettierignore
 .prettierrc
+jsconfig.json
 CHANGELOG.md
 CODE_OF_CONDUCT.md
 CONTRIBUTING.md
diff --git a/jsconfig.json b/jsconfig.json
new file mode 100644
index 000000000..b395a4546
--- /dev/null
+++ b/jsconfig.json
@@ -0,0 +1,10 @@
+{
+	"compilerOptions": {
+		// "checkJs": true,
+		// "strict": true
+		"lib": ["ES2022"],
+		"moduleResolution": "nodenext",
+		"resolveJsonModule": true
+	},
+	"exclude": ["dist", "node_modules"]
+}
diff --git a/package-lock.json b/package-lock.json
index 4b7949e91..7963f23e1 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -55,6 +55,7 @@
 			"devDependencies": {
 				"@commitlint/cli": "^17.6.7",
 				"@commitlint/config-conventional": "^17.6.7",
+				"@types/jest": "^29.5.3",
 				"autocannon": "^7.12.0",
 				"esbuild": "^0.18.14",
 				"esbuild-plugin-glob": "^2.2.2",
@@ -2531,6 +2532,16 @@
 				"@types/istanbul-lib-report": "*"
 			}
 		},
+		"node_modules/@types/jest": {
+			"version": "29.5.3",
+			"resolved": "https://registry.npmjs.org/@types/jest/-/jest-29.5.3.tgz",
+			"integrity": "sha512-1Nq7YrO/vJE/FYnqYyw0FS8LdrjExSgIiHyKg7xPpn+yi8Q4huZryKnkJatN1ZRH89Kw2v33/8ZMB7DuZeSLlA==",
+			"dev": true,
+			"dependencies": {
+				"expect": "^29.0.0",
+				"pretty-format": "^29.0.0"
+			}
+		},
 		"node_modules/@types/json-schema": {
 			"version": "7.0.12",
 			"resolved": "https://registry.npmjs.org/@types/json-schema/-/json-schema-7.0.12.tgz",
diff --git a/package.json b/package.json
index 17bb2c411..6820af710 100644
--- a/package.json
+++ b/package.json
@@ -75,6 +75,7 @@
 	"devDependencies": {
 		"@commitlint/cli": "^17.6.7",
 		"@commitlint/config-conventional": "^17.6.7",
+		"@types/jest": "^29.5.3",
 		"autocannon": "^7.12.0",
 		"esbuild": "^0.18.14",
 		"esbuild-plugin-glob": "^2.2.2",
diff --git a/src/plugins/doc-to-txt/plugin.test.js b/src/plugins/doc-to-txt/plugin.test.js
index 86a1a723c..a552c03bb 100644
--- a/src/plugins/doc-to-txt/plugin.test.js
+++ b/src/plugins/doc-to-txt/plugin.test.js
@@ -6,6 +6,9 @@ const sensible = require("@fastify/sensible");
 const plugin = require(".");
 
 describe("DOC-to-TXT conversion plugin", () => {
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
diff --git a/src/plugins/docx-to-html/plugin.test.js b/src/plugins/docx-to-html/plugin.test.js
index f414ec8c3..5914d4e34 100644
--- a/src/plugins/docx-to-html/plugin.test.js
+++ b/src/plugins/docx-to-html/plugin.test.js
@@ -7,6 +7,9 @@ const sensible = require("@fastify/sensible");
 const plugin = require(".");
 
 describe("DOCX-to-HTML conversion plugin", () => {
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
diff --git a/src/plugins/embed-html-images/plugin.test.js b/src/plugins/embed-html-images/plugin.test.js
index 326701bc3..558180b6d 100644
--- a/src/plugins/embed-html-images/plugin.test.js
+++ b/src/plugins/embed-html-images/plugin.test.js
@@ -8,6 +8,9 @@ const getConfig = require("../../config");
 
 describe("Embed-HTML-Images plugin", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
diff --git a/src/plugins/html-to-txt/plugin.test.js b/src/plugins/html-to-txt/plugin.test.js
index 263bdb9e4..8b1d23be5 100644
--- a/src/plugins/html-to-txt/plugin.test.js
+++ b/src/plugins/html-to-txt/plugin.test.js
@@ -7,6 +7,9 @@ const sensible = require("@fastify/sensible");
 const plugin = require(".");
 
 describe("HTML-to-TXT conversion plugin", () => {
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
diff --git a/src/plugins/image-to-txt/plugin.test.js b/src/plugins/image-to-txt/plugin.test.js
index 5b655475e..a95f882cb 100644
--- a/src/plugins/image-to-txt/plugin.test.js
+++ b/src/plugins/image-to-txt/plugin.test.js
@@ -9,6 +9,9 @@ const getConfig = require("../../config");
 
 describe("Image-to-TXT conversion plugin", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
diff --git a/src/plugins/pdf-to-html/plugin.test.js b/src/plugins/pdf-to-html/plugin.test.js
index 49243906a..16038e12d 100644
--- a/src/plugins/pdf-to-html/plugin.test.js
+++ b/src/plugins/pdf-to-html/plugin.test.js
@@ -21,6 +21,9 @@ const artifacts =
 
 describe("PDF-to-HTML conversion plugin", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -73,8 +76,8 @@ describe("PDF-to-HTML conversion plugin", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				lastPageToConvert: 2,
-				ignoreImages: false,
+				lastPageToConvert: "2",
+				ignoreImages: "false",
 				...query,
 			},
 			headers: {
@@ -97,10 +100,10 @@ describe("PDF-to-HTML conversion plugin", () => {
 			httpEquiv: expect.stringMatching(/^content-type$/iu),
 		});
 		expect(
-			dom.window.document.head.querySelector("title").textContent
+			dom.window.document.head.querySelector("title")?.textContent
 		).toMatch(/^docsmith_pdf-to-html_/u);
 		// String found in first paragraph of the test document
-		expect(dom.window.document.querySelector("p").textContent).toMatch(
+		expect(dom.window.document.querySelector("p")?.textContent).toMatch(
 			/for\sEngland\s/u
 		);
 		// String found in last paragraph of the test document
@@ -167,8 +170,8 @@ describe("PDF-to-HTML conversion plugin", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				lastPageToConvert: 1,
-				ignoreImages: false,
+				lastPageToConvert: "1",
+				ignoreImages: "false",
 			},
 			headers: {
 				"content-type": "application/pdf",
diff --git a/src/plugins/pdf-to-txt/plugin.test.js b/src/plugins/pdf-to-txt/plugin.test.js
index 1456cf968..b0244ec3d 100644
--- a/src/plugins/pdf-to-txt/plugin.test.js
+++ b/src/plugins/pdf-to-txt/plugin.test.js
@@ -14,6 +14,9 @@ const imageToTxt = require("../image-to-txt");
 
 describe("PDF-to-TXT conversion plugin", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -67,8 +70,8 @@ describe("PDF-to-TXT conversion plugin", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				firstPageToConvert: 2,
-				lastPageToConvert: 2,
+				firstPageToConvert: "2",
+				lastPageToConvert: "2",
 				...query,
 			},
 			headers: {
@@ -87,12 +90,12 @@ describe("PDF-to-TXT conversion plugin", () => {
 	it.each([
 		{
 			testName: "Converts PDF file to TXT using OCR",
-			query: { ocr: true },
+			query: { ocr: "true" },
 		},
 		{
 			testName:
 				"Converts PDF file to TXT using OCR and ignore invalid `test` query string param ",
-			query: { ocr: true, test: "test" },
+			query: { ocr: "true", test: "test" },
 		},
 	])("$testName", async ({ query }) => {
 		const response = await server.inject({
@@ -102,8 +105,8 @@ describe("PDF-to-TXT conversion plugin", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				firstPageToConvert: 1,
-				lastPageToConvert: 2,
+				firstPageToConvert: "1",
+				lastPageToConvert: "2",
 				...query,
 			},
 			headers: {
@@ -137,9 +140,9 @@ describe("PDF-to-TXT conversion plugin", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				firstPageToConvert: 2,
-				generateHtmlMetaFile: true,
-				lastPageToConvert: 2,
+				firstPageToConvert: "2",
+				generateHtmlMetaFile: "true",
+				lastPageToConvert: "2",
 			},
 			headers: {
 				"content-type": "application/pdf",
@@ -160,14 +163,14 @@ describe("PDF-to-TXT conversion plugin", () => {
 			httpEquiv: expect.stringMatching(/^content-type$/iu),
 		});
 		expect(
-			dom.window.document.head.querySelector("title").textContent
+			dom.window.document.head.querySelector("title")?.textContent
 		).toMatch(/^docsmith_pdf-to-txt_/u);
 		// String found at the start of the HTML document
-		expect(dom.window.document.querySelector("pre").textContent).toMatch(
+		expect(dom.window.document.querySelector("pre")?.textContent).toMatch(
 			"The NHS belongs to the people"
 		);
 		// String found at the end of the HTML document
-		expect(dom.window.document.querySelector("pre").textContent).toMatch(
+		expect(dom.window.document.querySelector("pre")?.textContent).toMatch(
 			/a full and transparent debate with the public, patients and staff.$/mu
 		);
 		expect(response.statusCode).toBe(200);
@@ -184,8 +187,8 @@ describe("PDF-to-TXT conversion plugin", () => {
 			testName: "is not a valid PDF file for OCR",
 			read: true,
 			query: {
-				lastPageToConvert: 1,
-				ocr: true,
+				lastPageToConvert: "1",
+				ocr: "true",
 			},
 		},
 	])(
@@ -224,7 +227,7 @@ describe("PDF-to-TXT conversion plugin", () => {
 			testName: "poppler.pdfToCairo() for OCR",
 			funcName: "pdfToCairo",
 			query: {
-				ocr: true,
+				ocr: "true",
 			},
 		},
 	])(
@@ -241,7 +244,7 @@ describe("PDF-to-TXT conversion plugin", () => {
 					"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 				),
 				query: {
-					lastPageToConvert: 1,
+					lastPageToConvert: "1",
 					...query,
 				},
 				headers: {
diff --git a/src/plugins/rtf-to-html/plugin.test.js b/src/plugins/rtf-to-html/plugin.test.js
index c312872d9..fbbda3670 100644
--- a/src/plugins/rtf-to-html/plugin.test.js
+++ b/src/plugins/rtf-to-html/plugin.test.js
@@ -21,6 +21,9 @@ const artifacts =
 
 describe("RTF-to-HTML conversion plugin", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -76,7 +79,7 @@ describe("RTF-to-HTML conversion plugin", () => {
 			httpEquiv: expect.stringMatching(/^content-type$/iu),
 		});
 		expect(
-			dom.window.document.head.querySelector("title").textContent
+			dom.window.document.head.querySelector("title")?.textContent
 		).toMatch(/^docsmith_rtf-to-html_/u);
 		// Check all images are removed
 		expect(dom.window.document.querySelectorAll("img")).toHaveLength(0);
diff --git a/src/plugins/tidy-css/plugin.test.js b/src/plugins/tidy-css/plugin.test.js
index 7aadcb1ca..024ffaf3a 100644
--- a/src/plugins/tidy-css/plugin.test.js
+++ b/src/plugins/tidy-css/plugin.test.js
@@ -8,6 +8,9 @@ const getConfig = require("../../config");
 
 describe("Tidy-CSS plugin", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -112,17 +115,17 @@ describe("Tidy-CSS plugin", () => {
 		// Check CSS is combined into one style tag
 		expect(dom.window.document.querySelectorAll("style")).toHaveLength(1);
 		// Check font-family is set to expected value
-		expect(style.innerHTML).toMatch(expected?.fonts || /./u);
+		expect(style?.innerHTML).toMatch(expected?.fonts || /./u);
 		// Check background-color is set to expected value
-		expect(style.innerHTML).toMatch(expected?.backgroundColor || /./u);
+		expect(style?.innerHTML).toMatch(expected?.backgroundColor || /./u);
 		// Check page-break-inside is set to avoid
-		expect(style.innerHTML).toMatch(
+		expect(style?.innerHTML).toMatch(
 			file !== "html_valid_no_style_type.html"
 				? /page-break-inside:avoid/u
 				: /./u
 		);
 		// Check CSS is tidied and minified
-		expect(style.innerHTML).not.toMatch(/;\}|<!--|--!?>|\n|\r/u);
+		expect(style?.innerHTML).not.toMatch(/;\}|<!--|--!?>|\n|\r/u);
 		expect(response.statusCode).toBe(200);
 	});
 
diff --git a/src/plugins/tidy-html/index.js b/src/plugins/tidy-html/index.js
index 1a67b448a..123eca301 100644
--- a/src/plugins/tidy-html/index.js
+++ b/src/plugins/tidy-html/index.js
@@ -3,6 +3,7 @@
 const { promisify } = require("util");
 const fp = require("fastify-plugin");
 const { JSDOM } = require("jsdom");
+// @ts-ignore
 const { minify } = require("html-minifier-terser");
 const { tidy } = require("htmltidy2");
 const { check } = require("language-tags");
diff --git a/src/plugins/tidy-html/plugin.test.js b/src/plugins/tidy-html/plugin.test.js
index d358bf168..87bbb369d 100644
--- a/src/plugins/tidy-html/plugin.test.js
+++ b/src/plugins/tidy-html/plugin.test.js
@@ -7,6 +7,9 @@ const sensible = require("@fastify/sensible");
 const plugin = require(".");
 
 describe("Tidy-HTML plugin", () => {
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeEach(() => {
@@ -62,10 +65,10 @@ describe("Tidy-HTML plugin", () => {
 		expect(response.body).toMatchSnapshot();
 		// Check language is set to default or options.language
 		expect(
-			dom.window.document.querySelector("html").getAttribute("lang")
+			dom.window.document.querySelector("html")?.getAttribute("lang")
 		).toBe(options?.language || "en");
 		expect(
-			dom.window.document.querySelector("html").getAttribute("xml:lang")
+			dom.window.document.querySelector("html")?.getAttribute("xml:lang")
 		).toBe(options?.language || "en");
 
 		// Check alt attributes are removed if options.removeAlt is true
diff --git a/src/routes/admin/healthcheck/route.test.js b/src/routes/admin/healthcheck/route.test.js
index 2ce04182f..037678d5b 100644
--- a/src/routes/admin/healthcheck/route.test.js
+++ b/src/routes/admin/healthcheck/route.test.js
@@ -10,6 +10,9 @@ const sharedSchemas = require("../../../plugins/shared-schemas");
 describe("Healthcheck route", () => {
 	describe("GET requests", () => {
 		let config;
+		/**
+		 * @type {Fastify.FastifyInstance}
+		 */
 		let server;
 
 		beforeAll(async () => {
diff --git a/src/routes/doc/txt/route.test.js b/src/routes/doc/txt/route.test.js
index 081990a53..dfd96b1c2 100644
--- a/src/routes/doc/txt/route.test.js
+++ b/src/routes/doc/txt/route.test.js
@@ -10,6 +10,9 @@ const sharedSchemas = require("../../../plugins/shared-schemas");
 
 describe("DOC-to-TXT route", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
diff --git a/src/routes/docs/openapi/route.test.js b/src/routes/docs/openapi/route.test.js
index 68a183d1c..e53757c9c 100644
--- a/src/routes/docs/openapi/route.test.js
+++ b/src/routes/docs/openapi/route.test.js
@@ -11,6 +11,9 @@ const sharedSchemas = require("../../../plugins/shared-schemas");
 describe("OpenAPI route", () => {
 	describe("GET requests", () => {
 		let config;
+		/**
+		 * @type {Fastify.FastifyInstance}
+		 */
 		let server;
 
 		beforeAll(async () => {
diff --git a/src/routes/docs/route.test.js b/src/routes/docs/route.test.js
index cd56e3d88..fe1d6da98 100644
--- a/src/routes/docs/route.test.js
+++ b/src/routes/docs/route.test.js
@@ -10,6 +10,9 @@ const sharedSchemas = require("../../plugins/shared-schemas");
 describe("Docs route", () => {
 	describe("GET requests", () => {
 		let config;
+		/**
+		 * @type {Fastify.FastifyInstance}
+		 */
 		let server;
 
 		beforeAll(async () => {
diff --git a/src/routes/docx/html/route.test.js b/src/routes/docx/html/route.test.js
index 13b8b8ecf..825fa20ca 100644
--- a/src/routes/docx/html/route.test.js
+++ b/src/routes/docx/html/route.test.js
@@ -13,6 +13,9 @@ const tidyHtml = require("../../../plugins/tidy-html");
 
 describe("DOCX-to-HTML route", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -73,7 +76,7 @@ describe("DOCX-to-HTML route", () => {
 			// eslint-disable-next-line security/detect-non-literal-fs-filename
 			body: await readFile(filePath),
 			query: {
-				removeAlt: true,
+				removeAlt: "true",
 			},
 			headers: {
 				accept: "application/json, text/html",
@@ -82,10 +85,9 @@ describe("DOCX-to-HTML route", () => {
 		});
 
 		expect(
-			response.body.replace(
-				/<title>[-\w]+<\/title>/gu,
-				"<title>docsmith</title>"
-			)
+			response.body
+				.toString()
+				.replace(/<title>[-\w]+<\/title>/gu, "<title>docsmith</title>")
 		).toMatchSnapshot();
 		expect(response.headers).toMatchObject({
 			"content-type": "text/html; charset=utf-8",
diff --git a/src/routes/docx/txt/route.test.js b/src/routes/docx/txt/route.test.js
index 89cc2375b..f863eacdc 100644
--- a/src/routes/docx/txt/route.test.js
+++ b/src/routes/docx/txt/route.test.js
@@ -10,6 +10,9 @@ const sharedSchemas = require("../../../plugins/shared-schemas");
 
 describe("DOCX-to-TXT route", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
diff --git a/src/routes/html/txt/route.test.js b/src/routes/html/txt/route.test.js
index 59ec45363..a9e11f406 100644
--- a/src/routes/html/txt/route.test.js
+++ b/src/routes/html/txt/route.test.js
@@ -11,6 +11,9 @@ const sharedSchemas = require("../../../plugins/shared-schemas");
 
 describe("HTML-to-TXT route", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -76,7 +79,7 @@ describe("HTML-to-TXT route", () => {
 				"./test_resources/test_files/html_invalid.html"
 			),
 			query: {
-				lastPageToConvert: 1,
+				lastPageToConvert: "1",
 			},
 			headers: {
 				accept: "application/json, text/plain",
diff --git a/src/routes/pdf/html/route.test.js b/src/routes/pdf/html/route.test.js
index 29c9308df..e1297895a 100644
--- a/src/routes/pdf/html/route.test.js
+++ b/src/routes/pdf/html/route.test.js
@@ -17,15 +17,18 @@ const tidyHtml = require("../../../plugins/tidy-html");
 // Generates 64 different combinations
 const queryStrings = generateCombos([
 	{ backgroundColor: "white" },
-	{ firstPageToConvert: 1 },
+	{ firstPageToConvert: "1" },
 	{ fonts: "Arial" },
-	{ ignoreImages: true },
-	{ noDrm: true },
-	{ removeAlt: true },
+	{ ignoreImages: "true" },
+	{ noDrm: "true" },
+	{ removeAlt: "true" },
 ]);
 
 describe("PDF-to-HTML route", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -52,7 +55,7 @@ describe("PDF-to-HTML route", () => {
 		await Promise.all(
 			queryStrings.map(async (queryString) => {
 				const query = queryString;
-				query.lastPageToConvert = 1;
+				query.lastPageToConvert = "1";
 
 				return server
 					.inject({
@@ -86,7 +89,7 @@ describe("PDF-to-HTML route", () => {
 		await Promise.all(
 			queryStrings.map((queryString) => {
 				const query = queryString;
-				query.lastPageToConvert = 1;
+				query.lastPageToConvert = "1";
 
 				return server
 					.inject({
@@ -117,7 +120,7 @@ describe("PDF-to-HTML route", () => {
 		await Promise.all(
 			queryStrings.map(async (queryString) => {
 				const query = queryString;
-				query.lastPageToConvert = 1;
+				query.lastPageToConvert = "1";
 
 				return server
 					.inject({
@@ -151,7 +154,7 @@ describe("PDF-to-HTML route", () => {
 		await Promise.all(
 			queryStrings.map(async (queryString) => {
 				const query = queryString;
-				query.lastPageToConvert = 1;
+				query.lastPageToConvert = "1";
 
 				return server
 					.inject({
@@ -188,7 +191,7 @@ describe("PDF-to-HTML route", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				lastPageToConvert: 1,
+				lastPageToConvert: "1",
 			},
 			headers: {
 				accept: "application/javascript",
diff --git a/src/routes/pdf/txt/route.test.js b/src/routes/pdf/txt/route.test.js
index 6b27e8244..23eb1f254 100644
--- a/src/routes/pdf/txt/route.test.js
+++ b/src/routes/pdf/txt/route.test.js
@@ -15,15 +15,18 @@ const tidyHtml = require("../../../plugins/tidy-html");
 
 // Generates 32 different combinations
 const queryStrings = generateCombos([
-	{ firstPageToConvert: 1 },
+	{ firstPageToConvert: "1" },
 	{ eolConvention: "unix" },
-	{ maintainLayout: true },
-	{ noDiagonalText: true },
-	{ noPageBreaks: true },
+	{ maintainLayout: "true" },
+	{ noDiagonalText: "true" },
+	{ noPageBreaks: "true" },
 ]);
 
 describe("PDF-to-TXT route", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -53,7 +56,7 @@ describe("PDF-to-TXT route", () => {
 		await Promise.all(
 			queryStrings.map(async (queryString) => {
 				const query = queryString;
-				query.lastPageToConvert = 1;
+				query.lastPageToConvert = "1";
 
 				return server
 					.inject({
@@ -90,8 +93,8 @@ describe("PDF-to-TXT route", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				lastPageToConvert: 1,
-				ocr: true,
+				lastPageToConvert: "1",
+				ocr: "true",
 			},
 			headers: {
 				accept: "application/json, text/plain",
@@ -115,8 +118,8 @@ describe("PDF-to-TXT route", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				generateHtmlMetaFile: true,
-				lastPageToConvert: 1,
+				generateHtmlMetaFile: "true",
+				lastPageToConvert: "1",
 			},
 			headers: {
 				accept: "application/json, text/html",
@@ -137,7 +140,7 @@ describe("PDF-to-TXT route", () => {
 		await Promise.all(
 			queryStrings.map((queryString) => {
 				const query = queryString;
-				query.lastPageToConvert = 1;
+				query.lastPageToConvert = "1";
 
 				return server
 					.inject({
@@ -168,7 +171,7 @@ describe("PDF-to-TXT route", () => {
 		await Promise.all(
 			queryStrings.map(async (queryString) => {
 				const query = queryString;
-				query.lastPageToConvert = 1;
+				query.lastPageToConvert = "1";
 
 				return server
 					.inject({
@@ -202,7 +205,7 @@ describe("PDF-to-TXT route", () => {
 		await Promise.all(
 			queryStrings.map(async (queryString) => {
 				const query = queryString;
-				query.lastPageToConvert = 1;
+				query.lastPageToConvert = "1";
 
 				return server
 					.inject({
@@ -239,7 +242,7 @@ describe("PDF-to-TXT route", () => {
 				"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 			),
 			query: {
-				lastPageToConvert: 1,
+				lastPageToConvert: "1",
 			},
 			headers: {
 				accept: "application/javascript",
diff --git a/src/routes/rtf/html/route.test.js b/src/routes/rtf/html/route.test.js
index 552d08c01..df04774ec 100644
--- a/src/routes/rtf/html/route.test.js
+++ b/src/routes/rtf/html/route.test.js
@@ -23,6 +23,9 @@ const queryStrings = generateCombos([
 
 describe("RTF-to-HTML route", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
diff --git a/src/routes/rtf/txt/route.test.js b/src/routes/rtf/txt/route.test.js
index 015393423..d5ee3b5b3 100644
--- a/src/routes/rtf/txt/route.test.js
+++ b/src/routes/rtf/txt/route.test.js
@@ -14,6 +14,9 @@ const tidyHtml = require("../../../plugins/tidy-html");
 
 describe("RTF-to-TXT route", () => {
 	let config;
+	/**
+	 * @type {Fastify.FastifyInstance}
+	 */
 	let server;
 
 	beforeAll(async () => {
@@ -79,7 +82,7 @@ describe("RTF-to-TXT route", () => {
 			url: "/",
 			body: await readFile("./test_resources/test_files/rtf_invalid.rtf"),
 			query: {
-				lastPageToConvert: 1,
+				lastPageToConvert: "1",
 			},
 			headers: {
 				accept: "application/json, text/plain",
diff --git a/src/server.test.js b/src/server.test.js
index f447f9b24..0f52e05ae 100644
--- a/src/server.test.js
+++ b/src/server.test.js
@@ -103,6 +103,9 @@ const expResHeaders5xxErrors = {
 describe("Server deployment", () => {
 	describe("Bearer token and OCR disabled", () => {
 		let config;
+		/**
+		 * @type {Fastify.FastifyInstance}
+		 */
 		let server;
 
 		beforeAll(async () => {
@@ -348,7 +351,7 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
+						lastPageToConvert: "1",
 					},
 					headers: {
 						accept: "application/json, text/html",
@@ -370,7 +373,7 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
+						lastPageToConvert: "1",
 					},
 					headers: {
 						accept: "application/javascript",
@@ -397,7 +400,7 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
+						lastPageToConvert: "1",
 					},
 					headers: {
 						accept: "application/json, text/plain",
@@ -461,6 +464,9 @@ describe("Server deployment", () => {
 
 	describe("Bearer token and OCR enabled", () => {
 		let config;
+		/**
+		 * @type {Fastify.FastifyInstance}
+		 */
 		let server;
 
 		beforeAll(async () => {
@@ -562,7 +568,7 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
+						lastPageToConvert: "1",
 					},
 					headers: {
 						accept: "application/json, text/html",
@@ -585,7 +591,7 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
+						lastPageToConvert: "1",
 					},
 					headers: {
 						accept: "application/json, text/html",
@@ -609,7 +615,7 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
+						lastPageToConvert: "1",
 					},
 					headers: {
 						accept: "application/javascript",
@@ -637,8 +643,8 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
-						ocr: true,
+						lastPageToConvert: "1",
+						ocr: "true",
 					},
 					headers: {
 						accept: "application/json, text/plain",
@@ -661,8 +667,8 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
-						ocr: true,
+						lastPageToConvert: "1",
+						ocr: "true",
 					},
 					headers: {
 						accept: "application/json, text/plain",
@@ -686,8 +692,8 @@ describe("Server deployment", () => {
 						"./test_resources/test_files/pdf_1.3_NHS_Constitution.pdf"
 					),
 					query: {
-						lastPageToConvert: 1,
-						ocr: true,
+						lastPageToConvert: "1",
+						ocr: "true",
 					},
 					headers: {
 						accept: "application/javascript",
@@ -709,8 +715,14 @@ describe("Server deployment", () => {
 
 	describe("CORS", () => {
 		let config;
-		let server;
+		/**
+		 * @type {{ [x: string]: any }}
+		 */
 		let currentEnv;
+		/**
+		 * @type {Fastify.FastifyInstance}
+		 */
+		let server;
 
 		beforeAll(() => {
 			Object.assign(process.env, {
@@ -729,7 +741,7 @@ describe("Server deployment", () => {
 				},
 				request: {
 					headers: {
-						origin: null,
+						origin: "",
 					},
 				},
 				expected: {
@@ -991,6 +1003,9 @@ describe("Server deployment", () => {
 
 	describe("API documentation", () => {
 		let config;
+		/**
+		 * @type {Fastify.FastifyInstance}
+		 */
 		let server;
 
 		beforeAll(async () => {
@@ -1008,6 +1023,7 @@ describe("Server deployment", () => {
 
 			// Turn off logging for test runs
 			config.fastifyInit.logger = undefined;
+			// @ts-ignore
 			server = Fastify({ ...config.fastifyInit, pluginTimeout: 0 });
 			await server.register(startServer, config).listen(config.fastify);
 		});
@@ -1089,6 +1105,9 @@ describe("Server deployment", () => {
 
 	describe("Error handling", () => {
 		let config;
+		/**
+		 * @type {Fastify.FastifyInstance}
+		 */
 		let server;
 
 		beforeAll(async () => {