diff --git a/packages/core/src/Id.ts b/packages/core/src/Id.ts
index 6f8c148d..187d6353 100644
--- a/packages/core/src/Id.ts
+++ b/packages/core/src/Id.ts
@@ -6,12 +6,13 @@ export type Tagged =
   | PropertyId
   | TheoremId
   | { kind: 'trait'; space: number; property: number }
+  | { kind: 'unknown'; id: number }
 
 export type SpaceId = { kind: 'space'; id: number }
 export type PropertyId = { kind: 'property'; id: number }
 export type TheoremId = { kind: 'theorem'; id: number }
 
-const pattern = /^(?<prefix>[spti])0*(?<id>\d+)/i
+const pattern = /^(?<prefix>[spti])?0*(?<id>\d+)/i
 
 export function traitId({ space, property }: TraitId): string {
   return `${space}|${property}`
@@ -33,6 +34,9 @@ export function tag(input: string): Tagged | null {
   }
 
   const id = parseInt(match.groups.id)
+  if (!match.groups.prefix) {
+    return { kind: 'unknown', id }
+  }
   switch (match.groups.prefix.toUpperCase()) {
     case 'S':
       return { kind: 'space', id }
diff --git a/packages/core/test/Id.test.ts b/packages/core/test/Id.test.ts
index 2b071f3c..f89c425d 100644
--- a/packages/core/test/Id.test.ts
+++ b/packages/core/test/Id.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { format, toInt, trim } from '../src/Id'
+import { format, toInt, trim, tag } from '../src/Id'
 
 describe('format', () => {
   it('pads the given character', () => {
@@ -16,13 +16,17 @@ describe('toInt', () => {
     expect(toInt('T000100')).toEqual(100)
   })
 
-  it('does not require a leading prefix', () => {
+  it('does not require leading zeros', () => {
     expect(toInt('P12')).toEqual(12)
   })
 
-  it('does not match unknown types', () => {
+  it('does not match nonexistent kinds', () => {
     expect(toInt('Z000100')).toEqual(0)
   })
+
+  it('matches unknown kind', () => {
+    expect(toInt('000123')).toEqual(123)
+  })
 })
 
 describe('trim', () => {
@@ -30,11 +34,41 @@ describe('trim', () => {
     expect(trim('T000100')).toEqual('100')
   })
 
-  it('does not require a leading prefix', () => {
+  it('does not require leading zeros', () => {
     expect(trim('P12')).toEqual('12')
   })
 
-  it('does not match unknown types', () => {
+  it('returns self for nonexistent kinds', () => {
     expect(trim('Z000100')).toEqual('Z000100')
   })
+
+  it('matches unknown kind', () => {
+    expect(trim('000123')).toEqual('123')
+  })
+})
+
+describe('tag', () => {
+  it('tags spaces', () => {
+    expect(tag('S000100')?.kind).toEqual('space')
+  })
+
+  it('tags properties', () => {
+    expect(tag('P000100')?.kind).toEqual('property')
+  })
+
+  it('tags theorems', () => {
+    expect(tag('T000100')?.kind).toEqual('theorem')
+  })
+
+  it('tags unknowns', () => {
+    expect(tag('000100')?.kind).toEqual('unknown')
+  })
+
+  it('is null for nonexistent kinds', () => {
+    expect(tag('X000100')).toEqual(null)
+  })
+
+  it('allows lowercase', () => {
+    expect(tag('s000100')?.kind).toEqual('space')
+  })
 })
diff --git a/packages/core/vite.config.ts b/packages/core/vite.config.ts
index ec2c34f9..a0f6f73c 100644
--- a/packages/core/vite.config.ts
+++ b/packages/core/vite.config.ts
@@ -17,10 +17,10 @@ export default defineConfig({
   },
   test: {
     coverage: {
-      lines: 91.04,
-      branches: 93.68,
-      statements: 91.04,
-      functions: 83.55,
+      lines: 91.19,
+      branches: 94.07,
+      statements: 91.19,
+      functions: 84.21,
       skipFull: true,
       thresholdAutoUpdate: true,
       exclude: ['src/Formula/Grammar.ts', 'test'],
diff --git a/packages/viewer/src/params/id.ts b/packages/viewer/src/params/id.ts
new file mode 100644
index 00000000..51d005bd
--- /dev/null
+++ b/packages/viewer/src/params/id.ts
@@ -0,0 +1,5 @@
+import type { ParamMatcher } from '@sveltejs/kit'
+
+export const match: ParamMatcher = param => {
+  return /^\w?(\d+)(.md)?$/.test(param)
+}
diff --git a/packages/viewer/src/routes/(app)/properties/[id]/+layout.ts b/packages/viewer/src/routes/(app)/properties/[id=id]/+layout.ts
similarity index 100%
rename from packages/viewer/src/routes/(app)/properties/[id]/+layout.ts
rename to packages/viewer/src/routes/(app)/properties/[id=id]/+layout.ts
diff --git a/packages/viewer/src/routes/(app)/properties/[id]/+page.svelte b/packages/viewer/src/routes/(app)/properties/[id=id]/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/properties/[id]/+page.svelte
rename to packages/viewer/src/routes/(app)/properties/[id=id]/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/properties/[id]/references/+page.svelte b/packages/viewer/src/routes/(app)/properties/[id=id]/references/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/properties/[id]/references/+page.svelte
rename to packages/viewer/src/routes/(app)/properties/[id=id]/references/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/properties/[id]/spaces/+page.svelte b/packages/viewer/src/routes/(app)/properties/[id=id]/spaces/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/properties/[id]/spaces/+page.svelte
rename to packages/viewer/src/routes/(app)/properties/[id=id]/spaces/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/properties/[id]/theorems/+page.svelte b/packages/viewer/src/routes/(app)/properties/[id=id]/theorems/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/properties/[id]/theorems/+page.svelte
rename to packages/viewer/src/routes/(app)/properties/[id=id]/theorems/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/spaces/[id]/+layout.ts b/packages/viewer/src/routes/(app)/spaces/[id=id]/+layout.ts
similarity index 100%
rename from packages/viewer/src/routes/(app)/spaces/[id]/+layout.ts
rename to packages/viewer/src/routes/(app)/spaces/[id=id]/+layout.ts
diff --git a/packages/viewer/src/routes/(app)/spaces/[id]/+page.svelte b/packages/viewer/src/routes/(app)/spaces/[id=id]/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/spaces/[id]/+page.svelte
rename to packages/viewer/src/routes/(app)/spaces/[id=id]/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/spaces/[id]/properties/+page.svelte b/packages/viewer/src/routes/(app)/spaces/[id=id]/properties/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/spaces/[id]/properties/+page.svelte
rename to packages/viewer/src/routes/(app)/spaces/[id=id]/properties/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/spaces/[id]/properties/[propertyId]/+page.svelte b/packages/viewer/src/routes/(app)/spaces/[id=id]/properties/[propertyId=id]/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/spaces/[id]/properties/[propertyId]/+page.svelte
rename to packages/viewer/src/routes/(app)/spaces/[id=id]/properties/[propertyId=id]/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/spaces/[id]/references/+page.svelte b/packages/viewer/src/routes/(app)/spaces/[id=id]/references/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/spaces/[id]/references/+page.svelte
rename to packages/viewer/src/routes/(app)/spaces/[id=id]/references/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/spaces/[id]/theorems/+page.svelte b/packages/viewer/src/routes/(app)/spaces/[id=id]/theorems/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/spaces/[id]/theorems/+page.svelte
rename to packages/viewer/src/routes/(app)/spaces/[id=id]/theorems/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/theorems/[id]/+layout.ts b/packages/viewer/src/routes/(app)/theorems/[id=id]/+layout.ts
similarity index 100%
rename from packages/viewer/src/routes/(app)/theorems/[id]/+layout.ts
rename to packages/viewer/src/routes/(app)/theorems/[id=id]/+layout.ts
diff --git a/packages/viewer/src/routes/(app)/theorems/[id]/+page.svelte b/packages/viewer/src/routes/(app)/theorems/[id=id]/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/theorems/[id]/+page.svelte
rename to packages/viewer/src/routes/(app)/theorems/[id=id]/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/theorems/[id]/converse/+page.svelte b/packages/viewer/src/routes/(app)/theorems/[id=id]/converse/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/theorems/[id]/converse/+page.svelte
rename to packages/viewer/src/routes/(app)/theorems/[id=id]/converse/+page.svelte
diff --git a/packages/viewer/src/routes/(app)/theorems/[id]/references/+page.svelte b/packages/viewer/src/routes/(app)/theorems/[id=id]/references/+page.svelte
similarity index 100%
rename from packages/viewer/src/routes/(app)/theorems/[id]/references/+page.svelte
rename to packages/viewer/src/routes/(app)/theorems/[id=id]/references/+page.svelte