diff --git a/eslint.config.js b/eslint.config.js
index ff446cd..2465ec0 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -4,7 +4,7 @@ import tsEslint from "typescript-eslint";
 
 const vitestEslintRecommended = vitestEslint.configs.recommended;
 
-/** @type {import("eslint").Linter.Config} */
+/** @type {import("eslint").Linter.Config[]} */
 export default [
 	{
 		ignores: ["lib/"],
@@ -17,12 +17,38 @@ export default [
 	cyfConfig,
 	...tsEslint.configs.strict,
 	...tsEslint.configs.stylistic,
+	...typeScriptOnly(
+		tsEslint.configs.strictTypeCheckedOnly,
+		tsEslint.configs.stylisticTypeCheckedOnly,
+	),
 	{
-		files: ["src/**/*.test.ts"],
+		files: ["setupTests.ts", "src/**/*.test.ts"],
 		...vitestEslintRecommended,
 		rules: {
 			"@typescript-eslint/no-non-null-assertion": "off",
+			"@typescript-eslint/no-unsafe-assignment": "off",
 			...vitestEslintRecommended.rules,
 		},
 	},
 ];
+
+/**
+ * Apply the supplied configurations only to TypeScript files.
+ *
+ * @param {import("eslint").Linter.Config[][]} configs
+ * @returns {import("eslint").Linter.Config[]}
+ */
+function typeScriptOnly(...configs) {
+	return configs.flat().map((config) => ({
+		...config,
+		files: [...(config.files ?? []), "**/*.ts"],
+		languageOptions: {
+			...config.languageOptions,
+			parserOptions: {
+				...config.languageOptions?.parserOptions,
+				projectService: true,
+				tsconfigRootDir: import.meta.dirname,
+			},
+		},
+	}));
+}
diff --git a/src/github.ts b/src/github.ts
index b25606f..d942198 100644
--- a/src/github.ts
+++ b/src/github.ts
@@ -18,7 +18,7 @@ export const validatePayload = async (body: string, signature: string): Promise<
 	if (!(await verify(secret, body, signature))) {
 		throw new Error("payload validation failed");
 	}
-	const payload: PingEvent | RepositoryEvent = JSON.parse(body);
+	const payload = JSON.parse(body) as PingEvent | RepositoryEvent;
 	if (!("action" in payload) || payload.action !== "created") {
 		console.log(`Ignoring event: ${"action" in payload ? payload.action : "ping"}`);
 		return;
diff --git a/src/netlify/slack_interaction.test.ts b/src/netlify/slack_interaction.test.ts
index f850dfc..352f534 100644
--- a/src/netlify/slack_interaction.test.ts
+++ b/src/netlify/slack_interaction.test.ts
@@ -169,12 +169,12 @@ describe("slack interaction handler", () => {
 		const timestamp = Math.floor(Date.now() / 1_000);
 		const body = new URLSearchParams(payload).toString();
 		const hmac = createHmac("sha256", secret);
-		hmac.update(`v0:${timestamp}:${body}`);
+		hmac.update(`v0:${timestamp.toFixed(0)}:${body}`);
 		const signature = hmac.digest("hex");
 		return { body, signature, timestamp };
 	};
 
 	const makeRequest = (body: string, signature: string, timestamp: number): Promise<HandlerResponse> => {
-		return handler({ body, headers: { "x-slack-request-timestamp": `${timestamp}`, "x-slack-signature": `v0=${signature}` } });
+		return handler({ body, headers: { "x-slack-request-timestamp": timestamp.toFixed(0), "x-slack-signature": `v0=${signature}` } });
 	};
 });
diff --git a/src/slack.test.ts b/src/slack.test.ts
index 468be12..f867107 100644
--- a/src/slack.test.ts
+++ b/src/slack.test.ts
@@ -4,20 +4,20 @@ import { validatePayload } from "./slack.js";
 import type { Maybe, MessageRef } from "./types.js";
 
 describe("validatePayload", () => {
-	it("rejects invalid version", async () => {
+	it("rejects invalid version", () => {
 		expect(() => attemptValidation({
 			signature: "v1=abc123",
 		})).toThrow("invalid signature version");
 	});
 
-	it("rejects old timestamp", async () => {
+	it("rejects old timestamp", () => {
 		expect(() => attemptValidation({
 			signature: "v0=abc123",
 			timestamp: Math.floor((Date.now() / 1_000) - (6 * 60)),
 		})).toThrow("timestamp too old");
 	});
 
-	it("rejects invalid hash", async () => {
+	it("rejects invalid hash", () => {
 		const body = "goodbye=world";
 		process.env.SLACK_SIGNING_SECRET = "keepitquiet";
 		const { signature, timestamp } = sign(body, "someothersecret");
@@ -28,7 +28,7 @@ describe("validatePayload", () => {
 		})).toThrow("payload validation failed");
 	});
 
-	it("turns the body into an object", async () => {
+	it("turns the body into an object", () => {
 		const body = `hello=world&payload=${JSON.stringify({})}`;
 		const secret = "secretsquirrel";
 		process.env.SLACK_SIGNING_SECRET = secret;
@@ -40,7 +40,7 @@ describe("validatePayload", () => {
 		})).toBeUndefined();
 	});
 
-	it("extracts the relevant delete action", async () => {
+	it("extracts the relevant delete action", () => {
 		const payload = {
 			actions: [{
 				action_id: "delete-repository",
@@ -71,7 +71,7 @@ describe("validatePayload", () => {
 		});
 	});
 
-	it("extracts the relevant dismiss action", async () => {
+	it("extracts the relevant dismiss action", () => {
 		const payload = {
 			actions: [{
 				action_id: "dismiss-deletion",
@@ -114,6 +114,6 @@ describe("validatePayload", () => {
 const sign = (payload: string, secret: string): { signature: string, timestamp: number } => {
 	const timestamp = Math.floor(Date.now() / 1_000);
 	const hmac = createHmac("sha256", secret);
-	hmac.update(`v0:${timestamp}:${payload}`);
+	hmac.update(`v0:${timestamp.toFixed(0)}:${payload}`);
 	return { signature: `v0=${hmac.digest("hex")}`, timestamp };
 };
diff --git a/src/slack.ts b/src/slack.ts
index 73b2f3d..6b4ecdd 100644
--- a/src/slack.ts
+++ b/src/slack.ts
@@ -80,7 +80,8 @@ export const validatePayload = (body: string, signature: string, timestamp: numb
 	if (!isValid(body, signature, timestamp)) {
 		throw new Error("payload validation failed");
 	}
-	return getPayload(JSON.parse(Object.fromEntries(new URLSearchParams(body).entries()).payload));
+	const payload = JSON.parse(Object.fromEntries(new URLSearchParams(body).entries()).payload) as SlackInteraction;
+	return getPayload(payload);
 };
 
 const actionsSection = (repo: Repository): ActionsBlock => ({
@@ -120,8 +121,8 @@ const fiveMinutesAgo = () => Math.floor((Date.now() / 1_000) - (5 * 60));
 
 const getPayload = ({ actions = [], message, user }: SlackInteraction): Maybe<MessageRef> => {
 	const action = actions.find(({ action_id }) => [DELETE_ACTION_ID, DISMISS_ACTION_ID].includes(action_id ?? ""));
-	if (action && action.value) {
-		const repo: Repository = JSON.parse(action.value);
+	if (action?.value) {
+		const repo = JSON.parse(action.value) as Repository;
 		return {
 			action: action.action_id === DELETE_ACTION_ID ? "delete" : "dismiss",
 			messageTs: message.ts,
@@ -153,7 +154,7 @@ const repoSection = ({ repoName, repoUrl, userLogin, userName, userUrl }: Reposi
 	const lines = [
 		`A new repository <${repoUrl}|\`${repoName}\`> was just created by <${userUrl}|${userName ? userName : `\`${userLogin}\``}>.`,
 	];
-	const match = repoUrl.match(/-\d+$/);
+	const match = /-\d+$/.exec(repoUrl);
 	if (match !== null) {
 		lines.push(`:redflag: *The \`${match[0]}\` makes this likely a mistake.*`);
 	}