Enhance calculators and SEO features, improve category handling, and update metadata for better indexing

hdyc-svelte/src/hooks.server.ts

@@ -1,4 +1,3 @@
-import path from 'node:path';
 import type { Handle } from '@sveltejs/kit';
 
 const MIME_TYPES: Record<string, string> = {
@@ -34,6 +33,8 @@ const LONG_CACHE_EXTENSIONS = new Set([
   '.otf'
 ]);
 
+const getExtension = (pathname: string): string => pathname.match(/\.[^./]+$/)?.[0].toLowerCase() ?? '';
+
 export const handle: Handle = async ({ event, resolve }) => {
   const response = await resolve(event);
   const pathname = event.url.pathname;
@@ -43,7 +44,7 @@ export const handle: Handle = async ({ event, resolve }) => {
     const existing = response.headers.get('content-type');
     const hasValidHeader = existing && existing.trim().length > 0;
     if (!hasValidHeader) {
-      const extension = path.extname(pathname).toLowerCase();
+      const extension = getExtension(pathname);
       const mime = extension && MIME_TYPES[extension];
       if (mime) {
         response.headers.set('content-type', mime);
@@ -61,7 +62,7 @@ export const handle: Handle = async ({ event, resolve }) => {
     return response;
   }
 
-  const extension = path.extname(pathname).toLowerCase();
+  const extension = getExtension(pathname);
   if (LONG_CACHE_EXTENSIONS.has(extension) && !contentType.includes('text/html')) {
     response.headers.set('cache-control', IMMUTABLE_ASSET_CACHE_CONTROL);
   }

hdyc-svelte/src/lib/components/Calculator.svelte

@@ -68,7 +68,7 @@
     }
 
     const manualField = swapState.originalField;
-    const manualValue = swapState.originalValue;
+    const manualValue = swapState.originalValue === null ? '' : String(swapState.originalValue);
     if (manualField === 1) val1 = manualValue;
     else val2 = manualValue;
     swapState = null;
@@ -441,6 +441,7 @@
     margin: 0;
   }
   .input-group input[type='number'] {
+    appearance: textfield;
     -moz-appearance: textfield;
   }
 

hdyc-svelte/src/lib/components/QuickConversionExample.svelte

@@ -26,11 +26,11 @@
     ? formatConversionValue(offset)
     : '';
   $: formulaExpression = supportsExample
-    ? `${exampleInput} × ${formattedFactorValue}${hasOffset ? ` + ${formattedOffsetValue}` : ''}`
+    ? `${exampleInput} x ${formattedFactorValue}${hasOffset ? ` ${offset > 0 ? '+' : '-'} ${formatConversionValue(Math.abs(offset))}` : ''}`
     : '';
 
   $: reverseExampleValue =
-    supportsExample && config.factor !== 0
+    supportsExample && typeof config.factor === 'number' && config.factor !== 0
       ? (1 - offset) / config.factor
       : null;
   $: formattedReverseValue = formatConversionValue(reverseExampleValue);
@@ -39,12 +39,18 @@
 {#if supportsExample && result}
   <section class="example-card">
     <h3>How to convert {config.labels.in1} to {config.labels.in2}</h3>
+    {#if hasOffset}
       <p class="example-note">
-      1 {config.labels.in1} = {formattedFactorValue}{hasOffset ? ` + ${formattedOffsetValue}` : ''} {config.labels.in2}
+        Formula: {config.labels.in2} = ({config.labels.in1} x {formattedFactorValue}) {offset > 0 ? '+' : '-'} {formatConversionValue(Math.abs(offset))}
+      </p>
+    {:else}
+      <p class="example-note">
+        1 {config.labels.in1} = {formattedFactorValue} {config.labels.in2}
       </p>
       <p class="example-note">
         1 {config.labels.in2} = {formattedReverseValue} {config.labels.in1}
       </p>
+    {/if}
     <p class="example-line">
       Example: convert {exampleInput} {config.labels.in1} to {config.labels.in2}
     </p>

hdyc-svelte/src/lib/components/Sidebar.svelte

@@ -148,7 +148,9 @@
     if ('addEventListener' in navBreakpoint) {
       navBreakpoint.addEventListener('change', handleNavChange);
     } else {
-      navBreakpoint.addListener(handleNavChange);
+      (navBreakpoint as MediaQueryList & {
+        addListener: (listener: (event: MediaQueryListEvent) => void) => void;
+      }).addListener(handleNavChange);
     }
 
     return () => {
@@ -156,7 +158,9 @@
       if ('removeEventListener' in navBreakpoint) {
         navBreakpoint.removeEventListener('change', handleNavChange);
       } else {
-        navBreakpoint.removeListener(handleNavChange);
+        (navBreakpoint as MediaQueryList & {
+          removeListener: (listener: (event: MediaQueryListEvent) => void) => void;
+        }).removeListener(handleNavChange);
       }
     };
   });

hdyc-svelte/src/lib/data/calculatorLoader.ts

@@ -7,8 +7,8 @@ export interface CalculatorDef {
   name: string;
   category: string;
   type: string;
-  teaser: string;
+  teaser?: string;
-  labels: { in1: string; in2: string };
+  labels: { in1: string; in2: string; in3?: string };
   factor?: number;
   offset?: number;
   hidden?: boolean;

hdyc-svelte/src/lib/data/calculators.ts

@@ -1,5 +1,5 @@
 // THIS FILE IS AUTO-GENERATED BY migrate.py
-export type CalcType = 'standard' | 'inverse' | '3col' | '3col-mul' | 'base' | 'text-bin' | 'bin-text' | 'dms-dd' | 'dd-dms' | 'dec-frac' | 'db-int' | 'db-spl' | 'db-v' | 'db-w' | 'awg' | 'brinell-rockwell' | 'ev-lux' | 'aov' | 'swg' | 'rockwell-vickers' | 'sus-cst' | 'molarity';
+export type CalcType = 'standard' | 'inverse' | '3col' | '3col-mul' | 'base' | 'text-bin' | 'bin-text' | 'dms-dd' | 'dd-dms' | 'dec-frac' | 'db-int' | 'db-spl' | 'db-v' | 'db-w' | 'awg' | 'awg-swg' | 'brinell-rockwell' | 'cmil-dia' | 'cmil-swg' | 'ev-lux' | 'aov' | 'swg' | 'rockwell-vickers' | 'sus-cst' | 'molarity';
 
 export interface CalculatorDef {
   slug: string;
@@ -3172,28 +3172,95 @@ const slugIndex: Map<string, CalculatorDef> = new Map(
 );
 
 
+const normalizedSlugCounts = calculators.reduce((counts, calc) => {
+  counts.set(calc.slug, (counts.get(calc.slug) ?? 0) + 1);
+  return counts;
+}, new Map<string, number>());
+
+const normalizeText = (value: string): string => value.toLowerCase().replace(/[^a-z0-9]+/g, ' ').trim();
+
+const labelsText = (calc: CalculatorDef): string =>
+  normalizeText([calc.name, calc.slug, calc.labels.in1, calc.labels.in2, calc.labels.in3 ?? ''].join(' '));
+
+const categoryRules: Array<[keyof typeof categories, RegExp]> = [
+  ['number-systems', /\b(binary|hex|hexadecimal|octal|decimal|ascii|fraction)\b/],
+  ['temperature', /\b(celsius|fahrenheit|kelvin|rankine|delisle)\b/],
+  ['data', /\b(bit|bits|byte|bytes|nibble|nibbles|baud|kilobyte|megabyte|gigabyte|terabyte|kibibyte|mebibyte|gibibyte|tebibyte)\b/],
+  ['electrical', /\b(volt|volts|amp|amps|ampere|amperes|ohm|ohms|siemens|farad|farads|henry|henries|coulomb|coulombs|kva)\b/],
+  ['radiation', /\b(becquerel|curie|gray|rad|sievert|rem|roentgen|rutherford|disintegrations)\b/],
+  ['light', /\b(lumen|lumens|lux|candela|foot candles?)\b/],
+  ['pressure', /\b(pascal|pascals|bar|psi|atmosphere|atmospheres|mmhg|torr|inches of water|inches of mercury|millimeters of mercury|water column)\b/],
+  ['power', /\b(watt|watts|kilowatt|kilowatts|megawatt|horsepower|btu hour|btu per hour|calories per second)\b/],
+  ['energy', /\b(joule|joules|calorie|calories|kilocalorie|btu|erg|therm|electron volt|watt hour|kilowatt hour)\b/],
+  ['force', /\b(force|torque|newton|newtons|dyne|dynes|foot pound|inch pound|pound force|kilogram force)\b/],
+  ['volume', /\b(cubic|liter|liters|litre|litres|gallon|gallons|cup|cups|pint|pints|quart|quarts|fluid|milliliter|milliliters|teaspoon|tablespoon|drop|bushel|peck|acre feet|acre foot|drams?)\b/],
+  ['area', /\b(square|acre|acres|hectare|hectares|are|ares|barn|barns|section|sections|township|townships)\b/],
+  ['speed', /\b(miles per hour|kilometers per hour|meters per second|feet per second|yards per second|knot|knots|mach|rpm|rads|hertz|furlongs per fortnight)\b/],
+  ['time', /\b(second|seconds|minute|minutes|hour|hours|day|days|week|weeks|month|months|year|years|nanosecond|microsecond|millisecond)\b/],
+  ['angle', /\b(degree|degrees|radian|radians|gradian|gradians|arcminute|arcminutes|arcsecond|arcseconds|mils)\b/],
+  ['weight', /\b(gram|grams|kilogram|kilograms|pound|pounds|ounce|ounces|carat|carats|stone|slug|ton|tons|pennyweight|grain|grains|momme|dalton|daltons|amu|atomic mass)\b/],
+  ['length', /\b(meter|meters|metre|metres|inch|inches|feet|foot|yard|yards|mile|miles|cable|cables|fathom|fathoms|rod|rods|chain|chains|nautical|league|leagues|angstrom|nanometer|centimeter|millimeter|micron)\b/],
+];
+
+export function getEffectiveCategory(calc: CalculatorDef): string {
+  const text = labelsText(calc);
+  const match = categoryRules.find(([, pattern]) => pattern.test(text));
+  return match?.[0] ?? calc.category;
+}
+
+export function isReliableCalculator(calc: CalculatorDef): boolean {
+  if (calc.type !== 'standard') return true;
+  if (typeof calc.factor === 'number' || typeof calc.offset === 'number') return true;
+  return normalizeText(calc.labels.in1) === normalizeText(calc.labels.in2);
+}
+
+export function isIndexableCalculator(calc: CalculatorDef): boolean {
+  return !calc.hidden && isReliableCalculator(calc) && normalizedSlugCounts.get(calc.slug) === 1;
+}
+
+export function getCanonicalSlug(calc: CalculatorDef): string {
+  if (!calc.hidden) return calc.slug;
+
+  const parts = calc.slug.match(/^(.*)-to-(.*)$/);
+  if (!parts) return calc.slug;
+
+  const reverseSlug = `${parts[2]}-to-${parts[1]}`;
+  const reverse = slugIndex.get(reverseSlug);
+  return reverse && isIndexableCalculator(reverse) ? reverse.slug : calc.slug;
+}
+
+export function getIndexableCalculators(): CalculatorDef[] {
+  const seen = new Set<string>();
+  return calculators.filter((calc) => {
+    if (!isIndexableCalculator(calc)) return false;
+    if (seen.has(calc.slug)) return false;
+    seen.add(calc.slug);
+    return true;
+  });
+}
+
 export function getCalculatorBySlug(slug: string): CalculatorDef | undefined {
   return slugIndex.get(slug);
 }
 
 export function getCalculatorsByCategory(category: string): CalculatorDef[] {
-  return calculators.filter(c => c.category === category && !c.hidden);
+  return getIndexableCalculators().filter(c => getEffectiveCategory(c) === category);
 }
 
 export function getCategoriesWithCounts(): { key: string; label: string; icon: string; count: number }[] {
   return Object.entries(categories).map(([key, meta]) => ({
     key,
     ...meta,
-    count: calculators.filter(c => c.category === key && !c.hidden).length,
+    count: getIndexableCalculators().filter(c => getEffectiveCategory(c) === key).length,
   }));
 }
 
 export function searchCalculators(query: string): CalculatorDef[] {
   const q = query.toLowerCase();
-  return calculators.filter(c =>
+  return getIndexableCalculators().filter(c =>
     (c.name.toLowerCase().includes(q) ||
     c.slug.includes(q) ||
     c.labels.in1.toLowerCase().includes(q) ||
-    c.labels.in2.toLowerCase().includes(q)) && !c.hidden
+    c.labels.in2.toLowerCase().includes(q))
   );
 }

hdyc-svelte/src/lib/data/unitDefinitions.ts

@@ -99,8 +99,31 @@ const normalizeLabel = (label?: string): string | undefined => {
 
 const categoryPriority = [...Object.keys(domainDefinitions)];
 
+const specificDefinitions: Array<[RegExp, string]> = [
+  [/\bwatts?\b|\bkilowatts?\b|\bmegawatts?\b|\bhorsepower\b/i, 'measures the rate at which energy is transferred or converted. It is used for engines, appliances, electrical loads, and heat-transfer rates.'],
+  [/\bcalories?\b|\bjoules?\b|\bbtu\b|\bkilocalories?\b|\btherms?\b|\bwatt hours?\b|\bkilowatt hours?\b/i, 'measures energy, heat, or work. These units are used for food energy, physics calculations, heating systems, and stored electricity.'],
+  [/\bvolts?\b/i, 'measures electric potential difference. Voltage describes the electrical pressure that pushes current through a circuit.'],
+  [/\bamps?\b|\bamperes?\b/i, 'measures electric current. Current describes how much electric charge flows through a circuit each second.'],
+  [/\bohms?\b/i, 'measures electrical resistance. Resistance describes how strongly a component opposes current flow.'],
+  [/\bfarads?\b/i, 'measures capacitance. Capacitance describes how much electric charge a component can store for a given voltage.'],
+  [/\bhenr(y|ies)\b/i, 'measures inductance. Inductance describes how strongly a circuit resists changes in current.'],
+  [/\bpascal|bar|psi|atmosphere|mmhg|torr|inches of water|inches of mercury/i, 'measures pressure, or force applied over an area. Pressure units are common in fluids, gases, weather, vacuum systems, and mechanical specifications.'],
+  [/\bcubic\b|\bliters?\b|\bgallons?\b|\bcups?\b|\bpints?\b|\bquarts?\b|\bfluid\b|\bbushels?\b|\bpecks?\b|\bacre[- ]feet\b|\bacre[- ]foot\b/i, 'measures volume or capacity. Volume units describe liquids, gases, containers, flow totals, and three-dimensional space.'],
+  [/\bsquare\b|\bacres?\b|\bhectares?\b|\bares?\b|\bbarns?\b|\bsections?\b|\btownships?\b/i, 'measures area or surface coverage. Area units are used for land, floors, materials, and two-dimensional spaces.'],
+  [/\bmeters per second\b|\bmiles per hour\b|\bkilometers per hour\b|\bfeet per second\b|\bknots?\b|\bmach\b|\brpm\b/i, 'measures speed, velocity, or rotation rate. These units describe motion over distance or repeated turns over time.'],
+  [/\bseconds?\b|\bminutes?\b|\bhours?\b|\bdays?\b|\bweeks?\b|\bmonths?\b|\byears?\b/i, 'measures time or duration. Time units describe intervals, schedules, rates, and elapsed periods.'],
+  [/\bdegrees?\b|\bradians?\b|\bgradians?\b|\barcminutes?\b|\barcseconds?\b/i, 'measures angle or rotation. Angle units describe turns, bearings, geometry, and circular motion.'],
+  [/\bgrams?\b|\bkilograms?\b|\bpounds?\b|\bounces?\b|\bcarats?\b|\btons?\b|\bdaltons?\b|\bamu\b/i, 'measures mass or weight. These units are used for materials, ingredients, shipping weights, laboratory quantities, and scientific mass scales.'],
+  [/\bbytes?\b|\bbits?\b|\bnibbles?\b|\bkilobytes?\b|\bmegabytes?\b|\bgigabytes?\b|\bterabytes?\b|\bkibibytes?\b|\bmebibytes?\b|\bgibibytes?\b/i, 'measures digital information or storage size. Data units are used for files, memory, transfer sizes, and storage devices.'],
+  [/\bbinary\b|\boctal\b|\bdecimal\b|\bhex\b|\bhexadecimal\b|\bascii\b/i, 'is a representation format for numbers or text. These systems define how values are encoded, displayed, or interpreted.'],
+  [/\bbecquerel|curie|gray|rad|sievert|rem|roentgen|rutherford/i, 'measures radioactivity, absorbed dose, or exposure. Radiation units describe decay rates, ionizing energy, and biological dose effects.'],
+];
+
 const buildDefinition = (label: string, categoryKey: string): string => {
   if (!label) return '';
+  const specific = specificDefinitions.find(([pattern]) => pattern.test(label));
+  if (specific) return `${label} ${specific[1]}`;
+
   const domain = domainDefinitions[categoryKey] || domainDefinitions.other;
   const description = [domain.summary, domain.context].filter(Boolean).join(' ');
   return `${label} ${description}`;

hdyc-svelte/src/lib/seo.ts

@@ -1,3 +1,6 @@
+import type { CalculatorDef } from '$lib/data/calculators';
+import { categories, getCanonicalSlug, getEffectiveCategory, isIndexableCalculator } from '$lib/data/calculators';
+
 export const SITE_URL = 'https://howdoyouconvert.com';
 export const SITE_NAME = 'HowDoYouConvert.com';
 export const DEFAULT_ROBOTS = 'index,follow';
@@ -10,6 +13,8 @@ type SeoInput = {
   description: string;
   pathname: string;
   type?: OpenGraphType;
+  canonical?: string;
+  robots?: string;
 };
 
 const normalizePathname = (pathname: string): string => {
@@ -23,11 +28,11 @@ const normalizePathname = (pathname: string): string => {
 
 export const canonicalUrl = (pathname: string): string => `${SITE_URL}${normalizePathname(pathname)}`;
 
-export const buildSeoMeta = ({ title, description, pathname, type = 'website' }: SeoInput) => {
+export const buildSeoMeta = ({ title, description, pathname, type = 'website', canonical: canonicalOverride, robots = DEFAULT_ROBOTS }: SeoInput) => {
-  const canonical = canonicalUrl(pathname);
+  const canonical = canonicalOverride ?? canonicalUrl(pathname);
   return {
     canonical,
-    robots: DEFAULT_ROBOTS,
+    robots,
     og: {
       type,
       title,
@@ -44,3 +49,52 @@ export const buildSeoMeta = ({ title, description, pathname, type = 'website' }:
 };
 
 export const toJsonLd = (value: unknown): string => JSON.stringify(value).replace(/</g, '\\u003c');
+
+export const escapeXml = (value: string): string =>
+  value
+    .replace(/&/g, '&amp;')
+    .replace(/</g, '&lt;')
+    .replace(/>/g, '&gt;')
+    .replace(/"/g, '&quot;')
+    .replace(/'/g, '&apos;');
+
+export const calculatorDescription = (calc: CalculatorDef): string => {
+  const category = categories[getEffectiveCategory(calc)]?.label ?? 'unit';
+  if (['3col', '3col-mul'].includes(calc.type)) {
+    return `Compute ${calc.labels.in3 ?? 'the derived value'} using ${calc.labels.in1} and ${calc.labels.in2}. Enter any two fields to solve the third.`;
+  }
+  return `Convert ${calc.labels.in1} to ${calc.labels.in2} with a fast ${category.toLowerCase()} calculator. Includes a bidirectional converter, formula notes, examples, and reference values.`;
+};
+
+export const calculatorSeo = (calc: CalculatorDef) => {
+  const canonicalSlug = getCanonicalSlug(calc);
+  const noindex = canonicalSlug !== calc.slug || !isIndexableCalculator(calc);
+  const title = `${calc.name} — ${SITE_NAME}`;
+  const description = calculatorDescription(calc);
+  const canonical = canonicalUrl(`/${canonicalSlug}`);
+
+  return {
+    ...buildSeoMeta({
+      title,
+      description,
+      pathname: `/${calc.slug}`,
+      canonical,
+      robots: noindex ? 'noindex,follow' : DEFAULT_ROBOTS,
+    }),
+    title,
+    description,
+    canonicalUrl: canonical,
+    noindex,
+  };
+};
+
+export const calculatorJsonLd = (calc: CalculatorDef, url: string) => ({
+  '@context': 'https://schema.org',
+  '@type': 'WebApplication',
+  name: `${calc.name} Converter`,
+  url,
+  applicationCategory: 'UtilitiesApplication',
+  operatingSystem: 'Any',
+  isAccessibleForFree: true,
+  description: calculatorDescription(calc),
+});

hdyc-svelte/src/routes/+layout.svelte

@@ -166,17 +166,23 @@
       if ('removeEventListener' in mediaQuery) {
         mediaQuery.removeEventListener('change', handlePreferenceChange);
       } else {
-        mediaQuery.removeListener(handlePreferenceChange);
+        (mediaQuery as MediaQueryList & {
+          removeListener: (listener: (event: MediaQueryListEvent) => void) => void;
+        }).removeListener(handlePreferenceChange);
       }
       if ('removeEventListener' in navBreakpoint) {
         navBreakpoint.removeEventListener('change', handleNavBreakpoint);
       } else {
-        navBreakpoint.removeListener(handleNavBreakpoint);
+        (navBreakpoint as MediaQueryList & {
+          removeListener: (listener: (event: MediaQueryListEvent) => void) => void;
+        }).removeListener(handleNavBreakpoint);
       }
       if ('removeEventListener' in headerBreakpoint) {
         headerBreakpoint.removeEventListener('change', handleHeaderBreakpoint);
       } else {
-        headerBreakpoint.removeListener(handleHeaderBreakpoint);
+        (headerBreakpoint as MediaQueryList & {
+          removeListener: (listener: (event: MediaQueryListEvent) => void) => void;
+        }).removeListener(handleHeaderBreakpoint);
       }
       if (idleCallbackId !== null && typeof appWindow.cancelIdleCallback === 'function') {
         appWindow.cancelIdleCallback(idleCallbackId);
@@ -193,18 +199,24 @@
     if ('addEventListener' in mediaQuery) {
       mediaQuery.addEventListener('change', handlePreferenceChange);
     } else {
-      mediaQuery.addListener(handlePreferenceChange);
+      (mediaQuery as MediaQueryList & {
+        addListener: (listener: (event: MediaQueryListEvent) => void) => void;
+      }).addListener(handlePreferenceChange);
     }
 
     if ('addEventListener' in navBreakpoint) {
       navBreakpoint.addEventListener('change', handleNavBreakpoint);
     } else {
-      navBreakpoint.addListener(handleNavBreakpoint);
+      (navBreakpoint as MediaQueryList & {
+        addListener: (listener: (event: MediaQueryListEvent) => void) => void;
+      }).addListener(handleNavBreakpoint);
     }
     if ('addEventListener' in headerBreakpoint) {
       headerBreakpoint.addEventListener('change', handleHeaderBreakpoint);
     } else {
-      headerBreakpoint.addListener(handleHeaderBreakpoint);
+      (headerBreakpoint as MediaQueryList & {
+        addListener: (listener: (event: MediaQueryListEvent) => void) => void;
+      }).addListener(handleHeaderBreakpoint);
     }
 
     return cleanup;

hdyc-svelte/src/routes/[slug]/+page.server.ts

@@ -1,8 +1,9 @@
 import { error } from '@sveltejs/kit';
 import type { PageServerLoad } from './$types';
-import { getCalculatorBySlug, getCalculatorsByCategory, categories } from '$lib/data/calculators';
+import { getCalculatorBySlug, getCalculatorsByCategory, categories, getEffectiveCategory } from '$lib/data/calculators';
+import { calculatorJsonLd, calculatorSeo } from '$lib/seo';
 
-export const load: PageServerLoad = ({ params }) => {
+export const load: PageServerLoad = ({ params, setHeaders }) => {
   const calc = getCalculatorBySlug(params.slug);
 
   if (!calc) {
@@ -11,16 +12,26 @@ export const load: PageServerLoad = ({ params }) => {
     });
   }
 
-  // Get related calculators from the same category (excluding this one)
+  const effectiveCategory = getEffectiveCategory(calc);
-  const related = getCalculatorsByCategory(calc.category)
+
+  const related = getCalculatorsByCategory(effectiveCategory)
     .filter(c => c.slug !== calc.slug)
     .slice(0, 8);
 
-  const categoryMeta = categories[calc.category];
+  const categoryMeta = categories[effectiveCategory];
+  const seo = calculatorSeo(calc);
+  if (seo.noindex) {
+    setHeaders({
+      'X-Robots-Tag': 'noindex, follow'
+    });
+  }
 
   return {
     calculator: calc,
     related,
+    seo,
+    jsonLd: JSON.stringify(calculatorJsonLd(calc, seo.canonicalUrl)),
+    category: effectiveCategory,
     categoryLabel: categoryMeta?.label ?? calc.category,
     categoryIcon: categoryMeta?.icon ?? '🔢'
   };

hdyc-svelte/src/routes/[slug]/+page.svelte

@@ -1,20 +1,20 @@
 <script lang="ts">
   import Calculator from '$lib/components/Calculator.svelte';
   import type { PageData } from './$types';
-  import { buildSeoMeta, canonicalUrl, SITE_NAME, SITE_URL, toJsonLd } from '$lib/seo';
+  import { buildSeoMeta, canonicalUrl, calculatorDescription, SITE_NAME, SITE_URL, toJsonLd } from '$lib/seo';
 
   export let data: PageData;
 
   $: calc = data.calculator;
   $: related = data.related;
-  $: pageTitle = `${calc.name} — ${SITE_NAME}`;
+  $: pageTitle = data.seo?.title ?? `${calc.name} — ${SITE_NAME}`;
-  $: pageDescription = ['3col', '3col-mul'].includes(calc.type)
+  $: pageDescription = data.seo?.description ?? calculatorDescription(calc);
-    ? `Compute ${calc.labels.in3 ?? 'the derived value'} using ${calc.labels.in1} and ${calc.labels.in2}. Enter any two fields to solve the third.`
-    : `Convert ${calc.labels.in1} to ${calc.labels.in2} instantly with our free online calculator. Accurate two-way conversion with the exact formula shown.`;
   $: seo = buildSeoMeta({
     title: pageTitle,
     description: pageDescription,
     pathname: `/${calc.slug}`,
+    canonical: data.seo?.canonicalUrl,
+    robots: data.seo?.robots,
   });
   $: breadcrumbJsonLd = toJsonLd({
     '@context': 'https://schema.org',
@@ -30,7 +30,7 @@
         '@type': 'ListItem',
         position: 2,
         name: data.categoryLabel,
-        item: canonicalUrl(`/category/${calc.category}`),
+        item: canonicalUrl(`/category/${data.category}`),
       },
       {
         '@type': 'ListItem',
@@ -75,7 +75,7 @@
 <nav class="breadcrumbs" aria-label="Breadcrumb">
   <ol>
     <li><a href="/">Home</a></li>
-    <li><a href="/category/{calc.category}">{data.categoryIcon} {data.categoryLabel}</a></li>
+    <li><a href="/category/{data.category}">{data.categoryIcon} {data.categoryLabel}</a></li>
     <li aria-current="page">{calc.name}</li>
   </ol>
 </nav>
@@ -91,18 +91,19 @@
     {@html calc.descriptionHTML}
   {:else}
     <h3>How to convert {calc.labels.in1} to {calc.labels.in2}</h3>
-    {#if calc.type === 'standard' && calc.factor}
+    {#if calc.type === 'standard' && (calc.factor || calc.offset)}
       <p>
         The conversion between {calc.labels.in1.toLowerCase()} and {calc.labels.in2.toLowerCase()}
-        uses a fixed multiplication factor. One {calc.labels.in1.toLowerCase().replace(/s$/, '')} equals
+        uses {calc.offset ? 'a linear formula with an offset' : 'a fixed multiplication factor'}.
-        {calc.factor}{calc.offset ? ` plus an offset of ${calc.offset}` : ''} {calc.labels.in2.toLowerCase()}.
         {#if calc.offset}
           This offset is common in temperature conversions, where scales differ not just in magnitude but also in their zero point.
+        {:else}
+          One {calc.labels.in1.toLowerCase()} equals {calc.factor} {calc.labels.in2.toLowerCase()}.
         {/if}
       </p>
       <p>
-        To convert, multiply the value in {calc.labels.in1.toLowerCase()} by {calc.factor}{calc.offset ? `, then add ${calc.offset}` : ''}.
+        To convert, multiply the value in {calc.labels.in1.toLowerCase()} by {calc.factor ?? 1}{calc.offset ? `, then ${calc.offset > 0 ? 'add' : 'subtract'} ${Math.abs(calc.offset)}` : ''}.
-        To convert in the opposite direction, {calc.offset ? `subtract ${calc.offset}, then ` : ''}divide by {calc.factor}.
+        To convert in the opposite direction, {calc.offset ? `${calc.offset > 0 ? 'subtract' : 'add'} ${Math.abs(calc.offset)}, then ` : ''}divide by {calc.factor ?? 1}.
       </p>
     {:else if calc.type === '3col' || calc.type === '3col-mul'}
       <p>

hdyc-svelte/src/routes/category/[category]/+page.server.ts

@@ -2,7 +2,7 @@ import { error } from '@sveltejs/kit';
 import type { PageServerLoad } from './$types';
 import { getCalculatorsByCategory, categories } from '$lib/data/calculators';
 
-export const load: PageServerLoad = ({ params }) => {
+export const load: PageServerLoad = ({ params, setHeaders }) => {
   const cat = params.category;
   const meta = categories[cat];
 
@@ -11,6 +11,11 @@ export const load: PageServerLoad = ({ params }) => {
   }
 
   const calcs = getCalculatorsByCategory(cat);
+  if (calcs.length === 0) {
+    setHeaders({
+      'X-Robots-Tag': 'noindex, follow'
+    });
+  }
 
   return {
     category: cat,

hdyc-svelte/src/routes/category/[category]/+page.svelte

@@ -15,7 +15,7 @@
     card.style.setProperty('--calc-tooltip-translate', 'calc(-100% - 0.55rem)');
   };
 
-  const resetCalcTooltipPosition = (event: MouseEvent) => {
+  const resetCalcTooltipPosition = (event: MouseEvent | FocusEvent) => {
     const card = event.currentTarget as HTMLElement | null;
     if (!card) return;
     card.style.removeProperty('--calc-tooltip-left');
@@ -33,6 +33,7 @@
     title: pageTitle,
     description: pageDescription,
     pathname: categoryPath,
+    robots: data.calculators.length > 0 ? 'index,follow' : 'noindex,follow',
   });
   $: breadcrumbJsonLd = toJsonLd({
     '@context': 'https://schema.org',

hdyc-svelte/src/routes/sitemap.xml/+server.ts

@@ -1,18 +1,19 @@
 import type { RequestHandler } from './$types';
-import { calculators, categories } from '$lib/data/calculators';
+import { getCategoriesWithCounts, getIndexableCalculators } from '$lib/data/calculators';
+import { canonicalUrl, escapeXml } from '$lib/seo';
 
 export const GET: RequestHandler = async () => {
-	const calculatorUrls = calculators.map(
+	const calculatorUrls = getIndexableCalculators().map(
 		(calc) => `  <url>
-    <loc>https://howdoyouconvert.com/${calc.slug}</loc>
+    <loc>${escapeXml(canonicalUrl(`/${calc.slug}`))}</loc>
     <changefreq>monthly</changefreq>
     <priority>0.8</priority>
   </url>`
 	);
 
-	const categoryUrls = Object.keys(categories).map(
+	const categoryUrls = getCategoriesWithCounts().filter(category => category.count > 0).map(
 		(category) => `  <url>
-    <loc>https://howdoyouconvert.com/category/${category}</loc>
+    <loc>${escapeXml(canonicalUrl(`/category/${category.key}`))}</loc>
     <changefreq>weekly</changefreq>
     <priority>0.9</priority>
   </url>`
@@ -21,7 +22,7 @@ export const GET: RequestHandler = async () => {
 	const sitemap = `<?xml version="1.0" encoding="UTF-8"?>
 <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
   <url>
-    <loc>https://howdoyouconvert.com/</loc>
+    <loc>${escapeXml(canonicalUrl('/'))}</loc>
     <changefreq>weekly</changefreq>
     <priority>1.0</priority>
   </url>