diff --git a/src/tools/lsp/config.test.ts b/src/tools/lsp/config.test.ts
new file mode 100644
index 000000000..977b6af00
--- /dev/null
+++ b/src/tools/lsp/config.test.ts
@@ -0,0 +1,110 @@
+import { describe, test, expect, beforeEach, afterEach } from "bun:test"
+import { isServerInstalled } from "./config"
+import { mkdtempSync, rmSync, writeFileSync } from "fs"
+import { join } from "path"
+import { tmpdir } from "os"
+
+describe("isServerInstalled", () => {
+  let tempDir: string
+  let savedEnv: { [key: string]: string | undefined }
+
+  beforeEach(() => {
+    tempDir = mkdtempSync(join(tmpdir(), "lsp-config-test-"))
+    savedEnv = {
+      PATH: process.env.PATH,
+      Path: process.env.Path,
+      PATHEXT: process.env.PATHEXT,
+    }
+  })
+
+  afterEach(() => {
+    try {
+      rmSync(tempDir, { recursive: true, force: true })
+    } catch (e) {
+      console.error(`Failed to clean up temp dir: ${e}`)
+    }
+
+    const keys = ["PATH", "Path", "PATHEXT"]
+    for (const key of keys) {
+      const val = savedEnv[key]
+      if (val === undefined) {
+        delete process.env[key]
+      } else {
+        process.env[key] = val
+      }
+    }
+  })
+
+  test("detects executable in PATH", () => {
+    const binName = "test-lsp-server"
+    const ext = process.platform === "win32" ? ".cmd" : ""
+    const binPath = join(tempDir, binName + ext)
+    
+    writeFileSync(binPath, "echo hello")
+    
+    const pathSep = process.platform === "win32" ? ";" : ":"
+    process.env.PATH = `${tempDir}${pathSep}${process.env.PATH || ""}`
+
+    expect(isServerInstalled([binName])).toBe(true)
+  })
+
+  test("returns false for missing executable", () => {
+    expect(isServerInstalled(["non-existent-server"])).toBe(false)
+  })
+
+  if (process.platform === "win32") {
+    test("Windows: detects executable with Path env var", () => {
+       const binName = "test-lsp-server-case"
+       const binPath = join(tempDir, binName + ".cmd")
+       writeFileSync(binPath, "echo hello")
+
+       delete process.env.PATH
+       process.env.Path = tempDir
+
+       expect(isServerInstalled([binName])).toBe(true)
+    })
+
+    test("Windows: respects PATHEXT", () => {
+       const binName = "test-lsp-server-custom"
+       const binPath = join(tempDir, binName + ".COM")
+       writeFileSync(binPath, "echo hello")
+
+       process.env.PATH = tempDir
+       process.env.PATHEXT = ".COM;.EXE"
+
+       expect(isServerInstalled([binName])).toBe(true)
+    })
+    
+    test("Windows: ensures default extensions are checked even if PATHEXT is missing", () => {
+       const binName = "test-lsp-server-default"
+       const binPath = join(tempDir, binName + ".bat")
+       writeFileSync(binPath, "echo hello")
+
+       process.env.PATH = tempDir
+       delete process.env.PATHEXT
+
+       expect(isServerInstalled([binName])).toBe(true)
+    })
+
+    test("Windows: ensures default extensions are checked even if PATHEXT does not include them", () => {
+        const binName = "test-lsp-server-ps1"
+        const binPath = join(tempDir, binName + ".ps1")
+        writeFileSync(binPath, "echo hello")
+ 
+        process.env.PATH = tempDir
+        process.env.PATHEXT = ".COM"
+ 
+        expect(isServerInstalled([binName])).toBe(true)
+     })
+  } else {
+      test("Non-Windows: does not use windows extensions", () => {
+          const binName = "test-lsp-server-win"
+          const binPath = join(tempDir, binName + ".cmd")
+          writeFileSync(binPath, "echo hello")
+          
+          process.env.PATH = tempDir
+          
+          expect(isServerInstalled([binName])).toBe(false)
+      })
+  }
+})
diff --git a/src/tools/lsp/config.ts b/src/tools/lsp/config.ts
index b29f9ac63..10a6febcf 100644
--- a/src/tools/lsp/config.ts
+++ b/src/tools/lsp/config.ts
@@ -170,31 +170,46 @@ export function isServerInstalled(command: string[]): boolean {
   }
 
   const isWindows = process.platform === "win32"
-  const ext = isWindows ? ".exe" : ""
+  
+  let exts = [""]
+  if (isWindows) {
+    const pathExt = process.env.PATHEXT || ""
+    if (pathExt) {
+       const systemExts = pathExt.split(";").filter(Boolean)
+       exts = [...new Set([...exts, ...systemExts, ".exe", ".cmd", ".bat", ".ps1"])]
+    } else {
+       exts = ["", ".exe", ".cmd", ".bat", ".ps1"]
+    }
+  }
 
-  const pathEnv = process.env.PATH || ""
+  let pathEnv = process.env.PATH || ""
+  if (isWindows && !pathEnv) {
+    pathEnv = process.env.Path || ""
+  }
+  
   const pathSeparator = isWindows ? ";" : ":"
   const paths = pathEnv.split(pathSeparator)
 
   for (const p of paths) {
-    if (existsSync(join(p, cmd)) || existsSync(join(p, cmd + ext))) {
-      return true
+    for (const suffix of exts) {
+      if (existsSync(join(p, cmd + suffix))) {
+        return true
+      }
     }
   }
 
   const cwd = process.cwd()
-  const additionalPaths = [
-    join(cwd, "node_modules", ".bin", cmd),
-    join(cwd, "node_modules", ".bin", cmd + ext),
-    join(homedir(), ".config", "opencode", "bin", cmd),
-    join(homedir(), ".config", "opencode", "bin", cmd + ext),
-    join(homedir(), ".config", "opencode", "node_modules", ".bin", cmd),
-    join(homedir(), ".config", "opencode", "node_modules", ".bin", cmd + ext),
+  const additionalBases = [
+    join(cwd, "node_modules", ".bin"),
+    join(homedir(), ".config", "opencode", "bin"),
+    join(homedir(), ".config", "opencode", "node_modules", ".bin"),
   ]
 
-  for (const p of additionalPaths) {
-    if (existsSync(p)) {
-      return true
+  for (const base of additionalBases) {
+    for (const suffix of exts) {
+      if (existsSync(join(base, cmd + suffix))) {
+        return true
+      }
     }
   }