diff --git a/README.md b/README.md
index 16968a7..d4ee499 100644
--- a/README.md
+++ b/README.md
@@ -161,7 +161,7 @@ The router escalates automatically when a task turns out harder than it looked a
 
 ### Post-Edit Diagnostics — the Model Sees Its Own Mistakes
 
-After a successful edit, Klaat Code runs your project's typechecker/linter on the changed file (auto-detects eslint/biome, ruff, gofmt, or a configured command) and hands any errors straight back to the model in the same turn — it fixes them before returning control to you, instead of costing you a round-trip.
+After a successful edit, Klaat Code runs your project's typechecker/linter on the changed file (auto-detects eslint/biome, ruff, gofmt, rubocop, swiftlint, phpstan/pint, ktlint, shellcheck, or a configured command) and hands any errors straight back to the model in the same turn — it fixes them before returning control to you, instead of costing you a round-trip.
 
 ### Terminal UI with Real Syntax Highlighting
 
diff --git a/src/tools/diagnostics.test.ts b/src/tools/diagnostics.test.ts
index 4b6fa95..2d66267 100644
--- a/src/tools/diagnostics.test.ts
+++ b/src/tools/diagnostics.test.ts
@@ -2,7 +2,11 @@
 import { mkdtempSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
-import { runDiagnostics, configureDiagnostics } from "./diagnostics";
+import {
+  runDiagnostics,
+  configureDiagnostics,
+  resolveDiagnosticsCommand,
+} from "./diagnostics";
 
 let tmp: string;
 
@@ -51,3 +55,156 @@ describe("Ruby diagnostics (.rb)", () => {
     expect(result === null || typeof result === "string").toBe(true);
   });
 });
+
+/** Shared shape for PATH-gated language branches: never throw; null or string. */
+function expectSoftResult(absPath: string): void {
+  expect(() => runDiagnostics(absPath, tmp)).not.toThrow();
+  const result = runDiagnostics(absPath, tmp);
+  expect(result === null || typeof result === "string").toBe(true);
+}
+
+describe("Swift diagnostics (.swift)", () => {
+  test("never throws; skips when swiftlint absent", () => {
+    const absPath = join(tmp, "Foo.swift");
+    writeFileSync(absPath, "struct Foo {}\n");
+    expectSoftResult(absPath);
+  });
+
+  test("returns null when diagnostics disabled", () => {
+    configureDiagnostics({ enabled: false });
+    const absPath = join(tmp, "Bar.swift");
+    writeFileSync(absPath, "struct Bar {}\n");
+    expect(runDiagnostics(absPath, tmp)).toBeNull();
+  });
+});
+
+describe("PHP diagnostics (.php)", () => {
+  test("never throws; skips when phpstan/pint absent", () => {
+    const absPath = join(tmp, "foo.php");
+    writeFileSync(absPath, "<?php echo 1;\n");
+    expectSoftResult(absPath);
+  });
+
+  test("returns null when diagnostics disabled", () => {
+    configureDiagnostics({ enabled: false });
+    const absPath = join(tmp, "bar.php");
+    writeFileSync(absPath, "<?php echo 1;\n");
+    expect(runDiagnostics(absPath, tmp)).toBeNull();
+  });
+});
+
+describe("Kotlin diagnostics (.kt / .kts)", () => {
+  test("never throws for .kt when ktlint absent", () => {
+    const absPath = join(tmp, "Foo.kt");
+    writeFileSync(absPath, "fun main() {}\n");
+    expectSoftResult(absPath);
+  });
+
+  test("never throws for .kts when ktlint absent", () => {
+    const absPath = join(tmp, "build.kts");
+    writeFileSync(absPath, "plugins {}\n");
+    expectSoftResult(absPath);
+  });
+
+  test("returns null when diagnostics disabled", () => {
+    configureDiagnostics({ enabled: false });
+    const absPath = join(tmp, "Bar.kt");
+    writeFileSync(absPath, "class Bar\n");
+    expect(runDiagnostics(absPath, tmp)).toBeNull();
+  });
+});
+
+describe("Shell diagnostics (.sh / .bash)", () => {
+  test("never throws for .sh when shellcheck absent", () => {
+    const absPath = join(tmp, "script.sh");
+    writeFileSync(absPath, "#!/bin/sh\necho hi\n");
+    expectSoftResult(absPath);
+  });
+
+  test("never throws for .bash when shellcheck absent", () => {
+    const absPath = join(tmp, "script.bash");
+    writeFileSync(absPath, "#!/bin/bash\necho hi\n");
+    expectSoftResult(absPath);
+  });
+
+  test("does not run shellcheck on .zsh (unsupported)", () => {
+    const absPath = join(tmp, "script.zsh");
+    writeFileSync(absPath, "#!/bin/zsh\necho hi\n");
+    const cmd = resolveDiagnosticsCommand(absPath, tmp, { onPath: () => true });
+    expect(cmd).toBeNull();
+  });
+
+  test("returns null when diagnostics disabled", () => {
+    configureDiagnostics({ enabled: false });
+    const absPath = join(tmp, "x.sh");
+    writeFileSync(absPath, "#!/bin/sh\ntrue\n");
+    expect(runDiagnostics(absPath, tmp)).toBeNull();
+  });
+});
+
+describe("resolveDiagnosticsCommand — positive PATH stubs", () => {
+  const present = (name: string) => (cmd: string) => cmd === name;
+
+  test("swiftlint argv", () => {
+    const abs = join(tmp, "A.swift");
+    const cmd = resolveDiagnosticsCommand(abs, tmp, { onPath: present("swiftlint") });
+    expect(cmd).toEqual(["swiftlint", "lint", "--quiet", "--reporter", "xcode", abs]);
+  });
+
+  test("phpstan preferred over pint", () => {
+    const abs = join(tmp, "a.php");
+    const cmd = resolveDiagnosticsCommand(abs, tmp, {
+      onPath: (c) => c === "phpstan" || c === "pint",
+    });
+    expect(cmd![0]).toBe("phpstan");
+    expect(cmd).toContain(abs);
+  });
+
+  test("pint used when phpstan absent; php alone is not enough", () => {
+    const abs = join(tmp, "a.php");
+    expect(resolveDiagnosticsCommand(abs, tmp, { onPath: present("pint") })![0]).toBe("pint");
+    expect(resolveDiagnosticsCommand(abs, tmp, { onPath: present("php") })).toBeNull();
+  });
+
+  test("ktlint argv has no --reporter flag", () => {
+    const abs = join(tmp, "A.kt");
+    expect(resolveDiagnosticsCommand(abs, tmp, { onPath: present("ktlint") }))
+      .toEqual(["ktlint", abs]);
+  });
+
+  test("shellcheck argv for .sh and .bash", () => {
+    const sh = join(tmp, "a.sh");
+    const bash = join(tmp, "a.bash");
+    expect(resolveDiagnosticsCommand(sh, tmp, { onPath: present("shellcheck") }))
+      .toEqual(["shellcheck", "-f", "gcc", sh]);
+    expect(resolveDiagnosticsCommand(bash, tmp, { onPath: present("shellcheck") }))
+      .toEqual(["shellcheck", "-f", "gcc", bash]);
+  });
+});
+
+describe("config override still wins for new extensions", () => {
+  test("explicit commands override PATH detection for .sh", () => {
+    configureDiagnostics({
+      enabled: true,
+      timeoutMs: 8_000,
+      commands: { ".sh": "echo 'script.sh:1:1: error: fake' >&2; exit 1" },
+    });
+    const absPath = join(tmp, "override.sh");
+    writeFileSync(absPath, "#!/bin/sh\n");
+    const result = runDiagnostics(absPath, tmp);
+    expect(result).not.toBeNull();
+    expect(result!).toContain("Diagnostics after this edit");
+    expect(result!).toContain("fake");
+  });
+
+  test("explicit clean override returns null for .swift", () => {
+    configureDiagnostics({
+      enabled: true,
+      timeoutMs: 8_000,
+      commands: { ".swift": "true" },
+    });
+    const absPath = join(tmp, "clean.swift");
+    writeFileSync(absPath, "struct Ok {}\n");
+    expect(runDiagnostics(absPath, tmp)).toBeNull();
+  });
+});
diff --git a/src/tools/diagnostics.ts b/src/tools/diagnostics.ts
index 46ee499..6e87431 100644
--- a/src/tools/diagnostics.ts
+++ b/src/tools/diagnostics.ts
@@ -35,15 +35,29 @@ function hasLocalBin(projectRoot: string, bin: string): boolean {
 }
 
 /** Is a command available on PATH? */
-function onPath(cmd: string): boolean {
+function onPathDefault(cmd: string): boolean {
   try {
     const r = spawnSync(process.platform === "win32" ? "where" : "which", [cmd], { timeout: 2000 });
     return r.status === 0;
   } catch { return false; }
 }
 
-/** Choose a fast per-file diagnostics command for a file, or null. */
-function commandFor(absPath: string, projectRoot: string): string[] | null {
+export interface CommandResolveDeps {
+  onPath?: (cmd: string) => boolean;
+  hasLocalBin?: (projectRoot: string, bin: string) => boolean;
+}
+
+/**
+ * Choose a fast per-file diagnostics command for a file, or null.
+ * Exported so tests can inject PATH/local-bin stubs and assert argv shape.
+ */
+export function resolveDiagnosticsCommand(
+  absPath: string,
+  projectRoot: string,
+  deps: CommandResolveDeps = {},
+): string[] | null {
+  const onPath = deps.onPath ?? onPathDefault;
+  const localBin = deps.hasLocalBin ?? hasLocalBin;
   const ext = extname(absPath).toLowerCase();
 
   // Explicit config override wins.
@@ -52,10 +66,10 @@ function commandFor(absPath: string, projectRoot: string): string[] | null {
 
   if ([".ts", ".tsx", ".js", ".jsx", ".mjs", ".cjs"].includes(ext)) {
     // Prefer a locally-installed linter (fast, per-file). Never npx-install.
-    if (hasLocalBin(projectRoot, "eslint")) {
+    if (localBin(projectRoot, "eslint")) {
       return [join(projectRoot, "node_modules", ".bin", "eslint"), "--no-color", "--format", "unix", absPath];
     }
-    if (hasLocalBin(projectRoot, "biome")) {
+    if (localBin(projectRoot, "biome")) {
       return [join(projectRoot, "node_modules", ".bin", "biome"), "check", "--no-colors", absPath];
     }
     return null;
@@ -73,6 +87,26 @@ function commandFor(absPath: string, projectRoot: string): string[] | null {
     if (onPath("rubocop")) return ["rubocop", "--format", "emacs", "--no-color", absPath];
     return null;
   }
+  if (ext === ".swift") {
+    if (onPath("swiftlint")) return ["swiftlint", "lint", "--quiet", "--reporter", "xcode", absPath];
+    return null;
+  }
+  if (ext === ".php") {
+    // Static analysis / style only — no php -l fallback (syntax-only is a different semantic level).
+    if (onPath("phpstan")) return ["phpstan", "analyse", "--no-progress", "--error-format=raw", absPath];
+    if (onPath("pint")) return ["pint", "--test", absPath];
+    return null;
+  }
+  if (ext === ".kt" || ext === ".kts") {
+    // No --reporter flag: ktlint 1.x changed reporter CLI; default plain output is fine.
+    if (onPath("ktlint")) return ["ktlint", absPath];
+    return null;
+  }
+  if (ext === ".sh" || ext === ".bash") {
+    // shellcheck does not support zsh — do not include .zsh (false positives).
+    if (onPath("shellcheck")) return ["shellcheck", "-f", "gcc", absPath];
+    return null;
+  }
   if (ext === ".rs") {
     // cargo check is whole-crate/slow — only via explicit config override.
     return null;
@@ -86,7 +120,7 @@ function commandFor(absPath: string, projectRoot: string): string[] | null {
  */
 export function runDiagnostics(absPath: string, projectRoot: string): string | null {
   if (!cfg.enabled) return null;
-  const cmd = commandFor(absPath, projectRoot);
+  const cmd = resolveDiagnosticsCommand(absPath, projectRoot);
   if (!cmd) return null;
 
   let out: string;