can1357/oh-my-pi · error · ToolError

Assertion failed

Error message

Assertion failed

What it means

The browser-run sandbox exposes an `assert(cond, text?)` helper to user scripts; when the condition is falsy it throws this ToolError so the run cell fails with an explicit assertion message. It exists so in-page invariant checks surface as tool errors naming the failed assertion rather than silent bad state downstream.

Source

Thrown at packages/coding-agent/src/tools/browser/tab-worker.ts:1293

		this.#active = active;
		let completed = false;
		let returnValue: unknown;
		let failure: { error: unknown } | undefined;
		let runPage: RunPageScope | undefined;
		try {
			throwIfAborted(signal);
			runPage = createRunPageScope(this.#requirePage());
			const browser = this.#requireBrowser();
			const tabApi = this.#createTabApi(msg.name, msg.timeoutMs, signal, msg.session, output, screenshots, active);
			const runtime = this.#ensureRuntime(msg.session);
			runtime.setCwd(msg.session.cwd);
			const onFloatingRejection = (reason: unknown): void => this.#recordFloatingRejection(active, reason);
			runtime.setRunScope({
				page: bindRunFacade(runPage.page, signal, active.rejectionOwner, onFloatingRejection),
				browser: bindRunFacade(browser, signal, active.rejectionOwner, onFloatingRejection),
				tab: bindRunFacade(tabApi, signal, active.rejectionOwner, onFloatingRejection),
				assert: (cond: unknown, text?: string): void => {
					if (!cond) throw new ToolError(text ?? "Assertion failed");
				},
				// Both wait forms register in the in-flight map so a cell that dies while
				// sleeping/polling names the culprit instead of a bare whole-cell timeout.
				wait: (msOrPredicate: number | (() => unknown), opts?: WaitPredicateOptions): Promise<unknown> => {
					const label = typeof msOrPredicate === "number" ? `wait(${msOrPredicate}ms)` : "wait(predicate)";
					const resolved =
						typeof msOrPredicate === "number"
							? undefined
							: { timeout: resolvePredicateTimeout(msg.timeoutMs, opts?.timeout), interval: opts?.interval };
					return observeBrowserRunPromise(
						this.#runOp(active, label, signal, Number.POSITIVE_INFINITY, sig =>
							waitForRun(msOrPredicate, sig, resolved),
						),
						active.rejectionOwner,
						onFloatingRejection,
					);
				},
			});

View on GitHub (pinned to 9690622007)

Solutions

  1. Read the supplied assertion text (or the default 'Assertion failed') and fix the violated condition in the run script
  2. Wait for the element/state before asserting (use the runtime's wait/predicate helpers)
  3. Pass a descriptive message to assert() so failures are diagnosable: `assert(el, 'login button present')`
  4. Re-run with snapshot/ariaSnapshot to inspect actual page state when the assertion is unexpected

Example fix

// before
assert(page.$('.price'), 'Assertion failed');
// after
await wait(() => page.$('.price'), { timeout: 5000 });
assert(page.$('.price'), 'price element should appear after load');
Defensive patterns

Strategy: try-catch

Validate before calling

// precondition check inside the run script before asserting
const el = page.$('.price');
if (!el) throw new Error('price element missing — check selector/page state before assert');

Try / catch

try {
  await runCell(code);
} catch (err) {
  if (err instanceof ToolError && err.message.includes('Assertion failed')) {
    const snap = await tab.ariaSnapshot(); // inspect actual page state
    logger.warn('run assertion failed', { snap });
  } else throw err;
}

Prevention

When it happens

Trigger: User automation code inside a browser-run cell calls `assert(...)` with a condition that evaluated false — e.g. asserting a selector matched, an element's text equals an expectation, or a URL/state check after navigation.

Common situations: Page rendered differently than the script assumed (A/B variant, locale, login wall); element not yet present at assert time (missing wait); wrong selector; flaky async content.

Related errors

AI-assisted analysis of can1357/oh-my-pi@9690622007 (2026-08-31). Data as JSON: /api/errors/c2ea190827507f77. Report an issue: GitHub.