diff --git a/bindings/js/README.md b/bindings/js/README.md
index 67792b4..85173ee 100644
--- a/bindings/js/README.md
+++ b/bindings/js/README.md
@@ -51,7 +51,7 @@ Every failure maps to one of the daemon's exit codes:
 | `VersionMismatchError` | 4 | the daemon's version differs from this package |
 | `InternalError` | 5 | internal daemon error |
 
-All derive from `ShellUseError` and carry `kind` and `exitCode`. `waitX` and `expectX` reject with `ExpectationError` on failure.
+All derive from `ShellUseError` and carry `kind` and `exitCode`. `waitX` and `expectX` reject with `ExpectationError` on failure. Assertion errors include the current visible terminal content.
 
 On its first call, a client checks that the running daemon's version matches the
 package version and throws `VersionMismatchError` if they differ. Stop the daemon
diff --git a/bindings/js/src/client.ts b/bindings/js/src/client.ts
index 25fa963..93d9131 100644
--- a/bindings/js/src/client.ts
+++ b/bindings/js/src/client.ts
@@ -5,6 +5,7 @@ import {
   resolveHome,
   resolveSession,
 } from "./config.js";
+import { ExpectationError } from "./errors.js";
 import { envPairs, unwrap } from "./protocol.js";
 import * as transport from "./transport.js";
 import { checkVersion } from "./version.js";
@@ -38,6 +39,21 @@ export interface MouseButtonOptions {
   button?: number;
 }
 
+function withOperation(error: unknown, operation: string): unknown {
+  if (!(error instanceof ExpectationError)) {
+    return error;
+  }
+  const previous = error.message;
+  error.message = `${operation}: ${previous}`;
+  if (error.stack) {
+    error.stack = error.stack.replace(
+      `${error.name}: ${previous}`,
+      `${error.name}: ${error.message}`,
+    );
+  }
+  return error;
+}
+
 class Mouse {
   #client: ShellUse;
 
@@ -281,17 +297,21 @@ export class ShellUse {
   }
 
   async expectText(text: string, opts: ExpectTextOptions = {}): Promise<void> {
-    await this.send({
-      kind: "expect_text",
-      text,
-      regex: opts.regex ?? false,
-      full: opts.full ?? false,
-      strict: opts.strict ?? true,
-      not: opts.not ?? false,
-      fg: opts.fg ?? null,
-      bg: opts.bg ?? null,
-      timeout_ms: opts.timeout ?? 5000,
-    });
+    try {
+      await this.send({
+        kind: "expect_text",
+        text,
+        regex: opts.regex ?? false,
+        full: opts.full ?? false,
+        strict: opts.strict ?? true,
+        not: opts.not ?? false,
+        fg: opts.fg ?? null,
+        bg: opts.bg ?? null,
+        timeout_ms: opts.timeout ?? 5000,
+      });
+    } catch (error) {
+      throw withOperation(error, "expectText");
+    }
   }
 
   async expectExitCode(code: number): Promise<void> {
diff --git a/bindings/js/test/integration.test.mjs b/bindings/js/test/integration.test.mjs
index 7ff74ca..3f93ec5 100644
--- a/bindings/js/test/integration.test.mjs
+++ b/bindings/js/test/integration.test.mjs
@@ -4,17 +4,22 @@ import { tmpdir } from "node:os";
 import { basename, join } from "node:path";
 import { test } from "node:test";
 
-import { ShellUse, sessions } from "../dist/index.js";
+import { ExpectationError, ShellUse, sessions } from "../dist/index.js";
 
 const BIN = process.env.SHELL_USE_BIN;
 const skip = !BIN;
+const shell = process.platform === "win32" ? "pwsh" : undefined;
+const evalArgs =
+  typeof globalThis.Deno === "undefined"
+    ? ["-e", "console.log('ready'); setInterval(() => {}, 1000)"]
+    : ["eval", "console.log('ready'); setInterval(() => {}, 1000)"];
 
 test("echo roundtrip drives a real session", { skip }, async () => {
   const home = mkdtempSync(join(tmpdir(), "shell-use-js-"));
   const session = `nodetest-${process.pid}-a`;
   const su = new ShellUse(session, { home });
   try {
-    await su.open();
+    await su.open({ shell });
     await su.submit("echo hello-sdk");
     await su.waitCommand();
     await su.expectText("hello-sdk", { strict: false });
@@ -26,11 +31,53 @@ test("echo roundtrip drives a real session", { skip }, async () => {
   }
 });
 
+test(
+  "assertion errors include the current terminal",
+  { skip },
+  async () => {
+    const home = mkdtempSync(join(tmpdir(), "shell-use-js-"));
+    const session = `nodetest-${process.pid}-error`;
+    const su = new ShellUse(session, { home });
+    try {
+      await su.run(process.execPath, evalArgs);
+      await su.waitText("ready", { timeout: 2000 });
+      await assert.rejects(
+        su.expectText("text-that-is-not-on-screen", { timeout: 50 }),
+        (error) =>
+          error instanceof ExpectationError &&
+          error.message.includes(
+            "expectText: timed out after 50ms waiting for 'text-that-is-not-on-screen' to be visible",
+          ) &&
+          error.message.includes("Terminal content:\n╭") &&
+          error.message.includes("ready") &&
+          error.message.includes("\n╰"),
+      );
+      await assert.rejects(
+        su.waitText("ready", { not: true, timeout: 50 }),
+        (error) =>
+          error instanceof ExpectationError &&
+          error.message.includes("timed out after 50ms waiting for 'ready' to be hidden") &&
+          error.message.includes("Terminal content:\n╭"),
+      );
+      await assert.rejects(
+        su.expectOutput("missing"),
+        (error) =>
+          error instanceof ExpectationError &&
+          error.message.includes("no command output tracked yet") &&
+          error.message.includes("Terminal content:\n╭") &&
+          error.message.includes("ready"),
+      );
+    } finally {
+      await su.close();
+    }
+  },
+);
+
 test("sessions lists an open session", { skip }, async () => {
   const home = mkdtempSync(join(tmpdir(), "shell-use-js-"));
   const session = `nodetest-${process.pid}-b`;
   const su = new ShellUse(session, { home });
-  await su.open();
+  await su.open({ shell });
   try {
     const names = await sessions({ home });
     assert.ok(names.includes(session));
@@ -47,7 +94,7 @@ test("snapshot lands in the client cwd", { skip }, async () => {
   const session = `nodetest-${process.pid}-c`;
   const su = new ShellUse(session, { home });
   try {
-    await su.open();
+    await su.open({ shell });
     await su.submit("echo snapshot-marker");
     await su.waitCommand();
     process.chdir(snapRoot);
diff --git a/bindings/python/README.md b/bindings/python/README.md
index 8f63112..1986a04 100644
--- a/bindings/python/README.md
+++ b/bindings/python/README.md
@@ -54,7 +54,7 @@ Every failure maps to one of the daemon's exit codes:
 | `VersionMismatchError` | 4 | the daemon's version differs from this package |
 | `InternalError` | 5 | internal daemon error |
 
-All derive from `ShellUseError`. `wait_*` and `expect_*` raise `ExpectationError` on failure.
+All derive from `ShellUseError`. `wait_*` and `expect_*` raise `ExpectationError` on failure. Assertion errors include the current visible terminal content.
 
 On its first call, a client checks that the running daemon's version matches the
 package version and raises `VersionMismatchError` if they differ. Stop the daemon
diff --git a/bindings/python/src/shell_use/client.py b/bindings/python/src/shell_use/client.py
index 30cf700..9fbcf43 100644
--- a/bindings/python/src/shell_use/client.py
+++ b/bindings/python/src/shell_use/client.py
@@ -6,7 +6,7 @@
 from . import _config as cfg
 from . import _transport as transport
 from ._protocol import EnvLike, env_pairs, unwrap
-from .errors import VersionMismatchError
+from .errors import ExpectationError, VersionMismatchError
 from .types import Cell, State
 
 
@@ -269,19 +269,24 @@ async def expect_text(
         bg: Optional[str] = None,
         timeout: int = 5000,
     ) -> None:
-        await self.send(
-            {
-                "kind": "expect_text",
-                "text": text,
-                "regex": regex,
-                "full": full,
-                "strict": strict,
-                "not": not_,
-                "fg": fg,
-                "bg": bg,
-                "timeout_ms": timeout,
-            }
-        )
+        try:
+            await self.send(
+                {
+                    "kind": "expect_text",
+                    "text": text,
+                    "regex": regex,
+                    "full": full,
+                    "strict": strict,
+                    "not": not_,
+                    "fg": fg,
+                    "bg": bg,
+                    "timeout_ms": timeout,
+                }
+            )
+        except ExpectationError as error:
+            error.message = f"expect_text: {error.message}"
+            error.args = (error.message,)
+            raise
 
     async def expect_exit_code(self, code: int) -> None:
         await self.send({"kind": "expect_exit_code", "code": code})
diff --git a/bindings/python/tests/test_integration.py b/bindings/python/tests/test_integration.py
index 6e7ffcc..1ed70ba 100644
--- a/bindings/python/tests/test_integration.py
+++ b/bindings/python/tests/test_integration.py
@@ -1,13 +1,15 @@
 import asyncio
 import os
+import sys
 import tempfile
 import unittest
 from pathlib import Path
 
 import shell_use
-from shell_use import ShellUse
+from shell_use import ExpectationError, ShellUse
 
 BIN = os.environ.get("SHELL_USE_BIN")
+SHELL = "pwsh" if sys.platform == "win32" else None
 
 
 def run(coro):
@@ -26,7 +28,7 @@ def _client(self):
     def test_echo_roundtrip(self):
         async def scenario():
             async with self._client() as su:
-                await su.open()
+                await su.open(shell=SHELL)
                 await su.submit("echo hello-sdk")
                 await su.wait_command()
                 await su.expect_text("hello-sdk", strict=False)
@@ -36,10 +38,34 @@ async def scenario():
 
         run(scenario())
 
+    def test_expect_text_error_includes_terminal(self):
+        async def scenario():
+            async with self._client() as su:
+                await su.run(
+                    sys.executable,
+                    "-c",
+                    "import sys,time; sys.stdout.write('ready'); "
+                    "sys.stdout.flush(); time.sleep(60)",
+                )
+                await su.wait_text("ready", timeout=2000)
+                with self.assertRaises(ExpectationError) as raised:
+                    await su.expect_text("text-that-is-not-on-screen", timeout=50)
+                message = str(raised.exception)
+                self.assertIn(
+                    "expect_text: timed out after 50ms waiting for "
+                    "'text-that-is-not-on-screen' to be visible",
+                    message,
+                )
+                self.assertIn("Terminal content:\n╭", message)
+                self.assertIn("ready", message)
+                self.assertIn("\n╰", message)
+
+        run(scenario())
+
     def test_sessions_lists_open_session(self):
         async def scenario():
             su = self._client()
-            await su.open()
+            await su.open(shell=SHELL)
             try:
                 names = await shell_use.sessions(home=self._home)
                 self.assertIn(self._session, names)
@@ -54,7 +80,7 @@ async def scenario():
             snap_root = tempfile.mkdtemp(prefix="shell-use-snap-")
             name = f"snap-{os.path.basename(snap_root)}"
             async with self._client() as su:
-                await su.open()
+                await su.open(shell=SHELL)
                 await su.submit("echo snapshot-marker")
                 await su.wait_command()
                 os.chdir(snap_root)
diff --git a/src/daemon/mod.rs b/src/daemon/mod.rs
index e350917..df7ca62 100644
--- a/src/daemon/mod.rs
+++ b/src/daemon/mod.rs
@@ -19,7 +19,7 @@ use crate::config::{self, POLL_DELAY_MS};
 use crate::input::{keys, mouse};
 use crate::ipc;
 use crate::monitor;
-use crate::protocol::{GetField, MouseAction, Request, Response};
+use crate::protocol::{ErrorKind, GetField, MouseAction, Request, Response};
 use crate::terminal::emu::{rows_to_strings, Color, EmuCell};
 use crate::terminal::locator::{self, Pattern};
 use logger::Logger;
@@ -348,7 +348,7 @@ fn text_of(rows: &[Vec<EmuCell>]) -> String {
 }
 
 fn dispatch(s: &mut Session, req: Request) -> Response {
-    match req {
+    let mut response = match req {
         Request::State => state(s),
         Request::Text { full } => Response::with(json!({ "text": text_of(&grid(s, full)) })),
         Request::Cells { x, y, w, h } => cells(s, x, y, w, h),
@@ -389,7 +389,13 @@ fn dispatch(s: &mut Session, req: Request) -> Response {
         } => do_snapshot(s, &name, update, include_colors, cwd),
         Request::Screenshot { full, path } => screenshot(s, full, path),
         _ => Response::internal("unsupported request"),
+    };
+    if response.kind == Some(ErrorKind::Assertion) {
+        if let Some(message) = response.message.take() {
+            response.message = Some(assertion_message(s, &message));
+        }
     }
+    response
 }
 
 fn act(r: anyhow::Result<()>) -> Response {
@@ -573,8 +579,10 @@ fn wait_text(
     );
     if found {
         Response::ok()
+    } else if not {
+        Response::assertion(timeout_message(&pattern.describe(), timeout_ms, true))
     } else {
-        Response::assertion(timeout_message(s, &pattern.describe(), timeout_ms))
+        Response::assertion(timeout_message(&pattern.describe(), timeout_ms, false))
     }
 }
 
@@ -655,10 +663,7 @@ fn expect_text(
         return if gone {
             Response::ok()
         } else {
-            Response::assertion(format!(
-                "expected '{}' to not be visible",
-                pattern.describe()
-            ))
+            Response::assertion(timeout_message(&pattern.describe(), timeout_ms, true))
         };
     }
 
@@ -687,7 +692,7 @@ fn expect_text(
     } else if let Some(err) = last_err {
         Response::assertion(err)
     } else {
-        Response::assertion(timeout_message(s, &pattern.describe(), timeout_ms))
+        Response::assertion(timeout_message(&pattern.describe(), timeout_ms, false))
     }
 }
 
@@ -822,9 +827,23 @@ fn screenshot(s: &Session, full: bool, path: Option<String>) -> Response {
     }
 }
 
-fn timeout_message(s: &Session, pattern: &str, timeout_ms: u64) -> String {
-    let snapshot = text_of(&viewable(s));
+fn timeout_message(pattern: &str, timeout_ms: u64, not: bool) -> String {
     format!(
-        "locator timeout: '{pattern}' not found after {timeout_ms}ms\n\nTerminal content:\n---START---\n{snapshot}\n---END---"
+        "timed out after {} waiting for '{pattern}' to be {}",
+        format_timeout(timeout_ms),
+        if not { "hidden" } else { "visible" }
     )
 }
+
+fn assertion_message(s: &Session, message: &str) -> String {
+    let screen = snapshot::serialize(&viewable(s), s.cols, false);
+    format!("{message}\n\nTerminal content:\n{screen}")
+}
+
+fn format_timeout(timeout_ms: u64) -> String {
+    if timeout_ms.is_multiple_of(1_000) {
+        format!("{}s", timeout_ms / 1_000)
+    } else {
+        format!("{timeout_ms}ms")
+    }
+}
diff --git a/src/terminal/locator.rs b/src/terminal/locator.rs
index a267ace..b62f110 100644
--- a/src/terminal/locator.rs
+++ b/src/terminal/locator.rs
@@ -74,7 +74,7 @@ pub fn find(
             }
             if occurrences > 1 && strict {
                 anyhow::bail!(
-                    "strict mode violation: getByText({}) resolved to {} elements",
+                    "strict mode expected one match for '{}', but found {}",
                     text,
                     occurrences
                 );
@@ -90,7 +90,7 @@ pub fn find(
             }
             if matches.len() > 1 && strict {
                 anyhow::bail!(
-                    "strict mode violation: getByText({}) resolved to {} elements",
+                    "strict mode expected one match for '{}', but found {}",
                     re.as_str(),
                     matches.len()
                 );