diff --git a/tests/parser-filter.test.ts b/tests/parser-filter.test.ts
new file mode 100644
index 0000000..4c34722
--- /dev/null
+++ b/tests/parser-filter.test.ts
@@ -0,0 +1,82 @@
+import { describe, it, expect } from 'vitest'
+
+import { filterProjectsByName } from '../src/parser.js'
+import type { ProjectSummary } from '../src/types.js'
+
+function makeProject(project: string, projectPath = project): ProjectSummary {
+  return {
+    project,
+    projectPath,
+    sessions: [],
+    totalCostUSD: 0,
+    totalApiCalls: 0,
+  }
+}
+
+describe('filterProjectsByName', () => {
+  const projects = [
+    makeProject('codeburn', '/Users/alice/codeburn'),
+    makeProject('AgentSeal', '/Users/alice/projects/AgentSeal'),
+    makeProject('dashboard', '/Users/alice/AgentSeal/dashboard'),
+    makeProject('sandbox', '/tmp/sandbox'),
+  ]
+
+  it('returns all projects when no filters given', () => {
+    expect(filterProjectsByName(projects)).toEqual(projects)
+    expect(filterProjectsByName(projects, [], [])).toEqual(projects)
+    expect(filterProjectsByName(projects, undefined, undefined)).toEqual(projects)
+  })
+
+  it('include matches project name (case-insensitive substring)', () => {
+    const result = filterProjectsByName(projects, ['codeburn'])
+    expect(result.map(p => p.project)).toEqual(['codeburn'])
+  })
+
+  it('include is case-insensitive', () => {
+    const result = filterProjectsByName(projects, ['AGENTSEAL'])
+    expect(result.map(p => p.project).sort()).toEqual(['AgentSeal', 'dashboard'])
+  })
+
+  it('include matches substring in path when name does not match', () => {
+    const result = filterProjectsByName(projects, ['alice/projects'])
+    expect(result.map(p => p.project)).toEqual(['AgentSeal'])
+  })
+
+  it('include uses OR semantics across patterns', () => {
+    const result = filterProjectsByName(projects, ['codeburn', 'sandbox'])
+    expect(result.map(p => p.project).sort()).toEqual(['codeburn', 'sandbox'])
+  })
+
+  it('exclude removes matching projects (AND-negation across patterns)', () => {
+    const result = filterProjectsByName(projects, undefined, ['codeburn', 'sandbox'])
+    expect(result.map(p => p.project).sort()).toEqual(['AgentSeal', 'dashboard'])
+  })
+
+  it('exclude matches path substring', () => {
+    const result = filterProjectsByName(projects, undefined, ['/tmp'])
+    expect(result.map(p => p.project)).not.toContain('sandbox')
+  })
+
+  it('exclude is applied after include', () => {
+    const result = filterProjectsByName(projects, ['AgentSeal'], ['dashboard'])
+    expect(result.map(p => p.project)).toEqual(['AgentSeal'])
+  })
+
+  it('returns empty array when no project matches include', () => {
+    expect(filterProjectsByName(projects, ['does-not-exist'])).toEqual([])
+  })
+
+  it('empty-string pattern matches every project', () => {
+    const resultInclude = filterProjectsByName(projects, [''])
+    expect(resultInclude).toHaveLength(projects.length)
+    const resultExclude = filterProjectsByName(projects, undefined, [''])
+    expect(resultExclude).toEqual([])
+  })
+
+  it('does not mutate the input array', () => {
+    const input = [makeProject('a'), makeProject('b')]
+    const snapshot = [...input]
+    filterProjectsByName(input, ['a'], ['b'])
+    expect(input).toEqual(snapshot)
+  })
+})