diff --git a/package-lock.json b/package-lock.json
index 1f36b81..935e9d4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1064,7 +1064,6 @@
       "resolved": "https://registry.npmjs.org/hono/-/hono-4.12.3.tgz",
       "integrity": "sha512-SFsVSjp8sj5UumXOOFlkZOG6XS9SJDKw0TbwFeV+AJ8xlST8kxK5Z/5EYa111UY8732lK2S/xB653ceuaoGwpg==",
       "license": "MIT",
-      "peer": true,
       "engines": {
         "node": ">=16.9.0"
       }
diff --git a/src/__tests__/agent-runner.test.ts b/src/__tests__/agent-runner.test.ts
index 631328b..6cbf505 100644
--- a/src/__tests__/agent-runner.test.ts
+++ b/src/__tests__/agent-runner.test.ts
@@ -1,9 +1,32 @@
-import { describe, it } from "node:test";
+import { describe, it, before, after } from "node:test";
 import assert from "node:assert/strict";
 import { AgentRunner } from "../agent-runner.js";
 import { createTask } from "../types.js";
+import { mkdtempSync, writeFileSync, mkdirSync, rmSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
 
 describe("AgentRunner", () => {
+  // Temp directories for language detection tests
+  let tsDir: string;
+  let pyDir: string;
+  let jsDir: string;
+
+  before(() => {
+    tsDir = mkdtempSync(join(tmpdir(), "test-ts-"));
+    writeFileSync(join(tsDir, "tsconfig.json"), "{}");
+    pyDir = mkdtempSync(join(tmpdir(), "test-py-"));
+    writeFileSync(join(pyDir, "pyproject.toml"), "");
+    jsDir = mkdtempSync(join(tmpdir(), "test-js-"));
+    writeFileSync(join(jsDir, "package.json"), "{}");
+  });
+
+  after(() => {
+    rmSync(tsDir, { recursive: true, force: true });
+    rmSync(pyDir, { recursive: true, force: true });
+    rmSync(jsDir, { recursive: true, force: true });
+  });
+
   // ── estimateCost ──
 
   it("estimateCost returns correct values for sonnet model", () => {
@@ -55,11 +78,36 @@ describe("AgentRunner", () => {
 
   // ── buildSystemPrompt ──
 
-  it("buildSystemPrompt includes tsc instruction", () => {
+  it("buildSystemPrompt includes tsc instruction for TypeScript projects", () => {
+    const runner = new AgentRunner();
+    const task = createTask("fix the bug");
+    const prompt = runner.buildSystemPrompt(task, tsDir);
+    assert.ok(prompt.includes("npx tsc"), "prompt should include npx tsc instruction for TS projects");
+  });
+
+  it("buildSystemPrompt includes python instructions for Python projects", () => {
+    const runner = new AgentRunner();
+    const task = createTask("fix the bug");
+    const prompt = runner.buildSystemPrompt(task, pyDir);
+    assert.ok(prompt.includes("test suite"), "prompt should include test suite instruction for Python projects");
+    assert.ok(prompt.includes("linter"), "prompt should include linter instruction for Python projects");
+    assert.ok(!prompt.includes("npx tsc"), "prompt should not include tsc for Python projects");
+  });
+
+  it("buildSystemPrompt includes npm test instruction for JavaScript projects", () => {
+    const runner = new AgentRunner();
+    const task = createTask("fix the bug");
+    const prompt = runner.buildSystemPrompt(task, jsDir);
+    assert.ok(prompt.includes("npm test"), "prompt should include npm test for JS projects");
+    assert.ok(!prompt.includes("npx tsc"), "prompt should not include tsc for JS projects");
+  });
+
+  it("buildSystemPrompt includes only commit instruction for unknown projects", () => {
     const runner = new AgentRunner();
     const task = createTask("fix the bug");
     const prompt = runner.buildSystemPrompt(task, "/nonexistent-path-xyz");
-    assert.ok(prompt.includes("npx tsc"), "prompt should include npx tsc instruction");
+    assert.ok(prompt.includes("git add -A"), "prompt should include commit instruction");
+    assert.ok(!prompt.includes("npx tsc"), "prompt should not include tsc for unknown projects");
   });
 
   it("buildSystemPrompt includes test runner hints for test-related tasks", () => {
@@ -188,11 +236,10 @@ describe("AgentRunner", () => {
     const runner = new AgentRunner();
     const task = createTask("hello", { agent: "echo", timeout: 5 });
     await runner.run(task, "/tmp");
-    // echo succeeds → output captured; verifyBuild fails (no tsconfig in /tmp) → status "failed" with [TSC_FAILED]
-    // Validates: (1) generic agent runs and captures output, (2) build verification is enforced
+    // echo succeeds → output captured; verifyBuild skips tsc (no tsconfig in /tmp) → status "success"
+    // Validates: (1) generic agent runs and captures output, (2) build verification is skipped for non-TS
     assert.ok(task.output.includes("hello"), "output should contain the prompt text from echo");
-    assert.strictEqual(task.status, "failed", "should fail due to tsc verification in /tmp");
-    assert.ok(task.output.startsWith("[TSC_FAILED]"), "output should be prefixed with [TSC_FAILED]");
+    assert.strictEqual(task.status, "success", "should succeed since /tmp is not a TS project");
     assert.ok(task.durationMs > 0, "durationMs should be recorded");
   });
 
@@ -253,13 +300,13 @@ describe("AgentRunner", () => {
     assert.strictEqual(typeof result.errors, "string");
   });
 
-  it("verifyBuild returns false when tsc fails", async () => {
+  it("verifyBuild skips tsc for non-TypeScript projects", async () => {
     const runner = new AgentRunner();
     const verify = (runner as unknown as { verifyBuild: (cwd: string) => Promise<{ ok: boolean; errors: string }> }).verifyBuild.bind(runner);
-    // /tmp has no tsconfig.json, so tsc will fail
+    // /tmp has no tsconfig.json, so verifyBuild should skip tsc and return ok
     const result = await verify("/tmp");
-    assert.strictEqual(result.ok, false);
-    assert.ok(result.errors.length > 0, "should have error message");
+    assert.strictEqual(result.ok, true, "should return ok for non-TS projects");
+    assert.strictEqual(result.errors, "", "should have no errors for non-TS projects");
   });
 
   // ── buildSystemPrompt edge cases ──
@@ -269,15 +316,15 @@ describe("AgentRunner", () => {
     const task = createTask("fix something");
     // Use actual project root where CLAUDE.md exists
     const prompt = runner.buildSystemPrompt(task, process.cwd() + "/../..");
-    // CLAUDE.md in project root has "## Development Rules" section
-    assert.ok(prompt.includes(".js"), "should include .js extension rule");
+    // Prompt should always include the commit instruction regardless of language
+    assert.ok(prompt.includes("git add -A"), "should include commit instruction");
   });
 
   it("buildSystemPrompt works without CLAUDE.md file", () => {
     const runner = new AgentRunner();
     const task = createTask("fix something");
     const prompt = runner.buildSystemPrompt(task, "/nonexistent-path");
-    assert.ok(prompt.includes("npx tsc"), "should still include tsc instruction");
+    assert.ok(prompt.includes("git add -A"), "should include commit instruction even without CLAUDE.md");
     assert.ok(prompt.length > 0);
   });
 
diff --git a/src/agent-runner.ts b/src/agent-runner.ts
index 6200fcc..2f0f117 100644
--- a/src/agent-runner.ts
+++ b/src/agent-runner.ts
@@ -3,7 +3,7 @@ import { log } from "./logger.js";
 import { spawn, type ChildProcess } from "node:child_process";
 import { exec as execCb } from "node:child_process";
 import { promisify } from "node:util";
-import { readFileSync } from "node:fs";
+import { readFileSync, existsSync } from "node:fs";
 
 const execAsync = promisify(execCb);
 
@@ -114,6 +114,13 @@ export class AgentRunner {
     return env;
   }
 
+  private detectLanguage(cwd: string): "typescript" | "javascript" | "python" | "unknown" {
+    if (existsSync(`${cwd}/tsconfig.json`)) return "typescript";
+    if (existsSync(`${cwd}/pyproject.toml`) || existsSync(`${cwd}/setup.py`) || existsSync(`${cwd}/setup.cfg`)) return "python";
+    if (existsSync(`${cwd}/package.json`)) return "javascript";
+    return "unknown";
+  }
+
   buildSystemPrompt(task: Task, cwd: string = process.cwd()): string {
     const parts: string[] = [];
 
@@ -128,9 +135,17 @@ export class AgentRunner {
       // CLAUDE.md not found – skip gracefully
     }
 
-    // Always-included instructions
-    parts.push("- Always use `.js` extensions in import paths (e.g. `import { foo } from \"./bar.js\"`).");
-    parts.push("- After making changes, run `npx tsc` to verify there are no type errors.");
+    // Language-aware instructions
+    const lang = this.detectLanguage(cwd);
+    if (lang === "typescript") {
+      parts.push("- Always use `.js` extensions in import paths (e.g. `import { foo } from \"./bar.js\"`).");
+      parts.push("- After making changes, run `npx tsc` to verify there are no type errors.");
+    } else if (lang === "python") {
+      parts.push("- After making changes, run the project's test suite to verify.");
+      parts.push("- Use the project's existing linter (ruff, flake8, etc.) if configured.");
+    } else if (lang === "javascript") {
+      parts.push("- After making changes, run `npm test` if configured.");
+    }
     parts.push("- Stage and commit all changes with `git add -A && git commit -m \"feat: <brief summary>\"`.");
 
     // Conditional: test or spec
@@ -241,7 +256,7 @@ export class AgentRunner {
     }
 
     const sysPrompt = this.buildSystemPrompt(task, cwd);
-    const fullPrompt = this.buildTaskPrompt(task);
+    const fullPrompt = this.buildTaskPrompt(task, cwd);
     const env = this.cleanEnv();
 
     const ac = new AbortController();
@@ -294,7 +309,7 @@ export class AgentRunner {
   private runClaude(task: Task, cwd: string, startMs: number, onEvent?: EventCallback): Promise<void> {
     return new Promise((resolve, reject) => {
       const sysPrompt = this.buildSystemPrompt(task, cwd);
-      const fullPrompt = this.buildTaskPrompt(task);
+      const fullPrompt = this.buildTaskPrompt(task, cwd);
 
       const args = [
         "-p",
@@ -431,7 +446,7 @@ export class AgentRunner {
   /** Run task using Codex CLI (exec mode with JSON output). */
   private runCodex(task: Task, cwd: string, startMs: number, onEvent?: EventCallback): Promise<void> {
     return new Promise((resolve, reject) => {
-      const fullPrompt = this.buildTaskPrompt(task);
+      const fullPrompt = this.buildTaskPrompt(task, cwd);
 
       const args = [
         "exec",
@@ -545,7 +560,7 @@ export class AgentRunner {
   /** Run task using any generic CLI command. The prompt is appended as the last argument. */
   private runGeneric(task: Task, cwd: string, agentCmd: string, startMs: number, onEvent?: EventCallback): Promise<void> {
     return new Promise((resolve, reject) => {
-      const fullPrompt = this.buildTaskPrompt(task);
+      const fullPrompt = this.buildTaskPrompt(task, cwd);
 
       // Split the agent command on whitespace: e.g. "aider --yes" → ["aider", "--yes"]
       const parts = agentCmd.split(/\s+/).filter(Boolean);
@@ -598,22 +613,43 @@ export class AgentRunner {
   }
 
   /** Build the full task prompt with instructions appended. */
-  private buildTaskPrompt(task: Task): string {
-    return `${task.prompt}
-
----
-
-## Instructions
+  private buildTaskPrompt(task: Task, cwd: string = process.cwd()): string {
+    const lang = this.detectLanguage(cwd);
+    const lines: string[] = [
+      `${task.prompt}`,
+      "",
+      "---",
+      "",
+      "## Instructions",
+      "",
+      "- **Minimal changes**: Only modify what is necessary to complete the task. Do not refactor, reformat, or touch unrelated code.",
+    ];
+
+    if (lang === "typescript") {
+      lines.push("- **TypeScript imports**: Always use `.js` extensions in import paths (e.g. `import { foo } from \"./bar.js\"`).");
+      lines.push("- **Type checking**: After making changes, run `npx tsc` to catch type errors.");
+      lines.push("- **Fix before committing**: If `npx tsc` fails, fix all errors before proceeding to commit.");
+      lines.push("- **Commit when done**: Stage and commit all changes with `git add -A && git commit -m \"feat: <brief summary>\"`.");
+    } else if (lang === "python") {
+      lines.push("- **Python project**: Use the project's build system (pyproject.toml / setup.py).");
+      lines.push("- **Verification**: Run relevant tests to verify changes work.");
+      lines.push("- **Commit when done**: Stage and commit with `git add -A && git commit -m \"feat: <brief summary>\"`.");
+    } else if (lang === "javascript") {
+      lines.push("- **Verification**: Run `npm test` if configured.");
+      lines.push("- **Commit when done**: Stage and commit with `git add -A && git commit -m \"feat: <brief summary>\"`.");
+    } else {
+      lines.push("- **Commit when done**: Stage and commit with `git add -A && git commit -m \"feat: <brief summary>\"`.");
+    }
 
-- **Minimal changes**: Only modify what is necessary to complete the task. Do not refactor, reformat, or touch unrelated code.
-- **TypeScript imports**: Always use \`.js\` extensions in import paths (e.g. \`import { foo } from "./bar.js"\`).
-- **Type checking**: After making changes, run \`npx tsc\` to catch type errors.
-- **Fix before committing**: If \`npx tsc\` fails, fix all errors before proceeding to commit.
-- **Commit when done**: Stage and commit all changes with \`git add -A && git commit -m "feat: <brief summary>"\`.`;
+    return lines.join("\n");
   }
 
   /** Async build verification — does not block the event loop. */
   private async verifyBuild(cwd: string): Promise<{ ok: boolean; errors: string }> {
+    const lang = this.detectLanguage(cwd);
+    if (lang !== "typescript") {
+      return { ok: true, errors: "" };
+    }
     try {
       await execAsync("npx tsc --noEmit", { cwd, encoding: "utf8" });
       return { ok: true, errors: "" };