diff --git a/code-generation/hap-gen.js b/code-generation/hap-gen.js
index c8cccfb..4b23084 100755
--- a/code-generation/hap-gen.js
+++ b/code-generation/hap-gen.js
@@ -24,9 +24,9 @@ for (const [name, service] of Object.entries(hap.Service)) {
 const code = format(
     `
 // Auto-generated by "${join(basename(__dirname), basename(__filename))}", don’t manually edit
-export const Uuids: Record<string,string> = ${JSON.stringify(uuidToServiceMap)} as const
+export const Uuids = ${JSON.stringify(uuidToServiceMap)} as const
 
-export const Services: Record<string,string> = ${JSON.stringify(serviceToUuidMap)} as const
+export const Services = ${JSON.stringify(serviceToUuidMap)} as const
 `,
     { filepath: 'codegen.ts', ...prettierConfig },
 )
diff --git a/src/adapters/http/api.ts b/src/adapters/http/api.ts
index 1424b93..e3a2131 100644
--- a/src/adapters/http/api.ts
+++ b/src/adapters/http/api.ts
@@ -21,10 +21,10 @@ export type HttpConfig = Pick<
 >
 
 export interface HttpServer {
-    log?: Logger
+    log: Logger | null
     config: HttpConfig
     serverFactory?: (requestListener: RequestListener) => Server
-    onRequest(): HttpResponse | undefined
+    onRequest(): HttpResponse | null
     onMetrics(): HttpResponse
     onNotFound(): HttpResponse
     onError(error: Error): HttpResponse
diff --git a/src/generated/services.ts b/src/generated/services.ts
index 92a4e80..039d557 100644
--- a/src/generated/services.ts
+++ b/src/generated/services.ts
@@ -1,5 +1,5 @@
 // Auto-generated by "code-generation/hap-gen.js", don’t manually edit
-export const Uuids: Record<string, string> = {
+export const Uuids = {
     '00000260-0000-1000-8000-0026BB765291': 'AccessCode',
     '000000DA-0000-1000-8000-0026BB765291': 'AccessControl',
     '0000003E-0000-1000-8000-0026BB765291': 'AccessoryInformation',
@@ -78,7 +78,7 @@ export const Uuids: Record<string, string> = {
     '0000008C-0000-1000-8000-0026BB765291': 'WindowCovering',
 } as const
 
-export const Services: Record<string, string> = {
+export const Services = {
     AccessCode: '00000260-0000-1000-8000-0026BB765291',
     AccessControl: '000000DA-0000-1000-8000-0026BB765291',
     AccessoryInformation: '0000003E-0000-1000-8000-0026BB765291',
diff --git a/src/metrics.ts b/src/metrics.ts
index 732fb87..3b793e0 100644
--- a/src/metrics.ts
+++ b/src/metrics.ts
@@ -1,13 +1,15 @@
 import type { Accessory, Device, Service } from './boundaries'
-import { Uuids } from './generated/services'
-import { assertTypeExhausted, isType } from './std'
+import { Services, Uuids } from './generated/services'
+import { assertTypeExhausted, isKeyOfConstObject, isType, strCamelCaseToSnakeCase } from './std'
+
+type Labels = Record<string, string>
 
 export class Metric {
     constructor(
         public readonly name: string,
         public readonly value: number,
         public readonly timestamp: Date | null = null,
-        public readonly labels: Record<string, string> = {},
+        public readonly labels: Labels = {},
     ) {}
 }
 
@@ -35,7 +37,7 @@ export function aggregate(devices: Device[], timestamp: Date): Metric[] {
     return metrics.flat()
 }
 
-function extractMetrics(service: Service, timestamp: Date, labels: Record<string, string>) {
+function extractMetrics(service: Service, timestamp: Date, labels: Labels): Metric[] {
     const metrics: Metric[] = []
 
     for (const characteristic of service.characteristics) {
@@ -63,7 +65,7 @@ function extractMetrics(service: Service, timestamp: Date, labels: Record<string
             case 'uint64':
                 {
                     const name = formatName(
-                        Uuids[service.type] || 'custom',
+                        isKeyOfConstObject(service.type, Uuids) ? Uuids[service.type] : 'custom',
                         characteristic.description,
                         characteristic.unit,
                     )
@@ -79,45 +81,35 @@ function extractMetrics(service: Service, timestamp: Date, labels: Record<string
     return metrics
 }
 
-export function formatName(serviceName: string, description: string, unit: string | undefined = undefined): string {
+export function formatName(serviceName: string, description: string, unit: string | null = null): string {
     return (
         [serviceName, description, typeof unit === 'string' ? unit.toLowerCase() : undefined]
             .filter(isType('string'))
-            .map((v) => camelCaseToSnakeCase(v))
+            .map((val) => strCamelCaseToSnakeCase(val))
             // Remove duplicate prefix
-            .reduce((carry, value) => (value.startsWith(carry) ? value : `${carry}_${value}`))
+            .reduce((carry, val) => (val.startsWith(carry) ? val : `${carry}_${val}`))
     )
 }
 
-function camelCaseToSnakeCase(str: string): string {
-    return str
-        .replace(/\B([A-Z][a-z])/g, ' $1')
-        .toLowerCase()
-        .trim()
-        .replace(/\s+/g, '_')
-}
-
-function getDeviceLabels(device: Device): Record<string, string> {
+function getDeviceLabels(device: Device): Labels {
     return {
         bridge: device.instance.name,
         device_id: device.instance.deviceID,
     }
 }
 
-function getAccessoryLabels(accessory: Accessory): Record<string, string> {
-    const labels: Record<string, string> = {}
-
+function getAccessoryLabels(accessory: Accessory): Labels {
     for (const service of accessory.services) {
-        if (service.type === '0000003E-0000-1000-8000-0026BB765291') {
+        if (service.type === Services.AccessoryInformation) {
             return getServiceLabels(service)
         }
     }
 
-    return labels
+    return {}
 }
 
-function getServiceLabels(service: Service): Record<string, string> {
-    const labels: Record<string, string> = {}
+function getServiceLabels(service: Service): Labels {
+    const labels: Labels = {}
 
     for (const characteristic of service.characteristics) {
         if (
@@ -134,7 +126,7 @@ function getServiceLabels(service: Service): Record<string, string> {
                 'Hardware Revision',
             ].includes(characteristic.description)
         ) {
-            labels[camelCaseToSnakeCase(characteristic.description)] = characteristic.value
+            labels[strCamelCaseToSnakeCase(characteristic.description)] = characteristic.value
         }
     }
 
diff --git a/src/platform.ts b/src/platform.ts
index 4bc6b06..c052d6b 100644
--- a/src/platform.ts
+++ b/src/platform.ts
@@ -8,7 +8,7 @@ import { type Config, ConfigBoundary, checkBoundary } from './boundaries'
 
 export class PrometheusExporterPlatform implements IndependentPlatformPlugin {
     private readonly httpServer: PrometheusServer
-    private httpServerController: HttpServerController | undefined = undefined
+    private httpServerController: HttpServerController | null = null
     private readonly config: Config
 
     constructor(public readonly log: Logger, config: PlatformConfig, public readonly api: API) {
diff --git a/src/prometheus.ts b/src/prometheus.ts
index df1da81..68f15df 100644
--- a/src/prometheus.ts
+++ b/src/prometheus.ts
@@ -1,12 +1,13 @@
-import type { Metric } from './metrics'
 import type { Logger } from 'homebridge'
 import type { HttpConfig, HttpResponse, HttpServer } from './adapters/http'
+import type { Metric } from './metrics'
+import { strTrimRight } from './std'
 
 export class MetricsRenderer {
     private readonly prefix: string
 
     constructor(prefix: string) {
-        this.prefix = trimRight(prefix, '_')
+        this.prefix = strTrimRight(prefix, '_')
     }
 
     render(metric: Metric): string {
@@ -21,7 +22,7 @@ export class MetricsRenderer {
 
     private renderLabels(labels: Metric['labels']): string {
         const rendered = Object.entries(labels)
-            .map(([key, value]) => `${sanitizePrometheusMetricName(key)}="${escapeAttributeValue(value)}"`)
+            .map(([label, val]) => `${sanitizePrometheusMetricName(label)}="${escapeAttributeValue(val)}"`)
             .join(',')
 
         return rendered !== '' ? '{' + rendered + '}' : ''
@@ -34,14 +35,6 @@ export class MetricsRenderer {
     }
 }
 
-function trimRight(str: string, char: string): string {
-    return stringReverse(stringReverse(str).replace(new RegExp(`^[${char}]+`), ''))
-}
-
-function stringReverse(str: string): string {
-    return str.split('').reverse().join('')
-}
-
 const retryAfterWhileDiscovery = 15
 const textContentType = 'text/plain; charset=utf-8'
 const prometheusSpecVersion = '0.0.4'
@@ -57,17 +50,19 @@ export class PrometheusServer implements HttpServer {
 
     constructor(
         public readonly config: HttpConfig,
-        public readonly log: Logger | undefined = undefined,
+        public readonly log: Logger | null = null,
         private readonly renderer: MetricsRenderer = new MetricsRenderer(config.prefix),
     ) {}
 
-    onRequest(): HttpResponse | undefined {
-        if (!this.metricsDiscovered) {
-            return {
-                statusCode: 503,
-                headers: withHeaders(textContentType, { 'Retry-After': String(retryAfterWhileDiscovery) }),
-                body: 'Metrics discovery pending',
-            }
+    onRequest(): HttpResponse | null {
+        if (this.metricsDiscovered) {
+            return null
+        }
+
+        return {
+            statusCode: 503,
+            headers: withHeaders(textContentType, { 'Retry-After': String(retryAfterWhileDiscovery) }),
+            body: 'Metrics discovery pending',
         }
     }
 
@@ -113,7 +108,7 @@ function escapeString(str: string) {
  *
  * `undefined` is converted to an empty string.
  */
-function escapeAttributeValue(str: string) {
+function escapeAttributeValue(str: Metric['labels'][keyof Metric['labels']]) {
     if (typeof str !== 'string') {
         str = JSON.stringify(str)
     }
diff --git a/src/std.ts b/src/std.ts
index 626362e..c1badb5 100644
--- a/src/std.ts
+++ b/src/std.ts
@@ -1,15 +1,41 @@
-type Types = 'string' | 'number' | 'boolean' | 'object'
 interface TypeMap {
     string: string
     number: number
+    bigint: bigint
     boolean: boolean
     object: object
+    symbol: symbol
+    undefined: undefined
 }
 
-export function isType<T extends Types>(type: T): (v: unknown) => v is TypeMap[T] {
+// Type predicate higher order function for use with e.g. filter or map
+export function isType<T extends keyof TypeMap>(type: T): (v: unknown) => v is TypeMap[T] {
     return (v: unknown): v is TypeMap[T] => typeof v === type
 }
 
+// Type predicate for object keys
+// Only safe for const objects, as other objects might carry additional, undeclared properties
+export function isKeyOfConstObject<T extends object>(key: string | number | symbol, obj: T): key is keyof T {
+    return key in obj
+}
+
+// Use for exhaustiveness checks in switch/case
 export function assertTypeExhausted(v: never): never {
     throw new Error(`Type should be exhausted but is not. Value "${JSON.stringify(v)}`)
 }
+
+export function strCamelCaseToSnakeCase(str: string): string {
+    return str
+        .replace(/\B([A-Z][a-z])/g, ' $1')
+        .toLowerCase()
+        .trim()
+        .replace(/\s+/g, '_')
+}
+
+export function strReverse(str: string): string {
+    return str.split('').reverse().join('')
+}
+
+export function strTrimRight(str: string, char: string): string {
+    return strReverse(strReverse(str).replace(new RegExp(`^[${char}]+`), ''))
+}