Verify that an exact quote appears on a web page.

Fetches url and confirms quote is present in its visible text. Use before attributing a statement to a source. Returns refuted if the page loads but the quote is absent -- i.e. the attribution is fabricated.

Verify that an arXiv id or DOI actually resolves, and return its real title.

Pass an arXiv id (e.g. '2412.18004' or 'arXiv:2412.18004') or a DOI. A 'checked' verdict includes the genuine title, so a plausible-looking but fabricated identifier is caught as 'refuted'.

Run a self-contained Python snippet and confirm its stdout contains expected_output.

WARNING: this executes the code. Only pass code you would run yourself; it is not sandboxed from the network or filesystem. Returns refuted if the snippet errors or prints something other than claimed.

Confirm that a string (or regex) actually occurs in files under a local path.

Use to verify a claim about what a codebase or document contains -- 'the README reports 0.9086', 'the function is defined in src/' -- rather than trusting the assertion. Returns the real matching lines.

Confirm an arithmetic expression equals a claimed result.

Evaluates expression (numeric literals and + - * / // % ** only) and compares to claimed_result. Catches arithmetic a model asserted without computing.