diff --git a/scripts/test-build-validation.ps1 b/scripts/test-build-validation.ps1
new file mode 100644
index 0000000..50f9e0e
--- /dev/null
+++ b/scripts/test-build-validation.ps1
@@ -0,0 +1,51 @@
+[CmdletBinding()]
+param()
+$ErrorActionPreference = 'Stop'
+$root = Split-Path $PSScriptRoot -Parent
+$work = Join-Path ([System.IO.Path]::GetTempPath()) ("ai-config-build-validation-" + [Guid]::NewGuid())
+New-Item $work -ItemType Directory -Force | Out-Null
+
+function New-RepoCopy {
+    $copy = Join-Path $work ("case-" + [Guid]::NewGuid())
+    New-Item $copy -ItemType Directory -Force | Out-Null
+    Get-ChildItem $root -Force | Where-Object { $_.Name -notin @('.git','generated') } | ForEach-Object {
+        Copy-Item $_.FullName (Join-Path $copy $_.Name) -Recurse -Force
+    }
+    return $copy
+}
+
+function Test-BuildFails([string]$Label, [scriptblock]$Mutate) {
+    $copy = New-RepoCopy
+    & $Mutate $copy
+    $failed = $false
+    try { & (Join-Path $copy 'scripts/build.ps1') 2>&1 | Out-Null }
+    catch { $failed = $true }
+    Remove-Item $copy -Recurse -Force -ErrorAction SilentlyContinue
+    if (-not $failed) { throw "Expected build to fail for case '$Label' but it succeeded." }
+}
+
+Test-BuildFails 'invalid Claude settings.json' {
+    param($copy)
+    Add-Content (Join-Path $copy 'adapters/claude/config/settings.json') '} this is not json {'
+}
+
+Test-BuildFails 'duplicate agent name' {
+    param($copy)
+    $architect = Join-Path $copy 'shared/agents/architect/agent.yml'
+    (Get-Content $architect -Raw) -replace 'name:\s*\S+', 'name: implementer' | Set-Content $architect -NoNewline
+}
+
+Test-BuildFails 'duplicate plugin name' {
+    param($copy)
+    $manifest = Join-Path $copy 'adapters/plugins.tsv'
+    $lines = Get-Content $manifest
+    Add-Content $manifest $lines[1]
+}
+
+Test-BuildFails 'leftover template placeholder' {
+    param($copy)
+    Add-Content (Join-Path $copy 'shared/global-instructions.md') "`n__NOT_A_REAL_PLACEHOLDER__"
+}
+
+Remove-Item $work -Recurse -Force -ErrorAction SilentlyContinue
+Write-Output 'PASS build validation: invalid JSON, duplicate agent, duplicate plugin, and leftover placeholders are all rejected'