Checks that the MCP server and the engine (sidecar) respond.

Complete documentation of the YATT test format (schema v1): fields, actions, variables, dataset and usage guide. Read it before creating tests.

Lists the saved reference images (visual asserts).

Returns a reference image as PNG (for visual comparison).

Lists the tests saved in the YATT library (names).

Returns a saved test as a full JSON object (steps, variables, environments, dataset).

Creates a new test. Accepts the content as a JSON string or as an object. Validates the schema (schemaVersion, steps, actions). Fails if the name already exists unless overwrite: true.

Replaces the full content of an existing test (same validation as test_create).

Deletes a test from the library (database and tests/.yatt.json file).

Renames a test in the library (updates the DB and the mirror file).

Duplicates an existing test under a new name (default " (copy)").

Validates test content (JSON string or object) without saving it. Returns {ok: true, doc: summary} or {ok: false, error}. Useful before test_create/test_update.

Generates the code of a saved test as a TypeScript spec (.spec.ts), in Playwright (@playwright/test) or Jest (jest-environment-playwright) format, with sub-flows embedded as functions. Returns the content; with write: true it saves the file into exports/.spec.ts like the app.

Lists the saved run reports (names .json and .html).

Returns the content of a report (parseable JSON). To diagnose failures, the report has steps[] with status ok/fail, error and ms.

Deletes a saved report (DB + file under reports/).

Executes a read-only query (SELECT/WITH/EXPLAIN/PRAGMA) against the app-under-test database. Pass the connection in db (SQLite path or "file:" / postgres:// URL); otherwise the engine-side YATT_APP_DB/--app-db configuration applies. Returns {columns, rows, totalRows}; rows are capped at 200.

Runs a saved test headless (Chromium engine by default) and saves a report in the library. Parameters: variable environment, per-run overrides, per-step timeout. Returns the summary with the steps and the report name.

Data-driven: runs a test once per row of overrides and returns each row result plus totals. No report is saved.

Open (or reopen) the controlled browser. headless=true by default; visible only when you need to point by hand.

Closes the controlled browser (clears the browser session).

State of the controlled browser: open/closed, engine, URL and interaction.

Captures the current viewport as a PNG image (the AI sees the page) + url, title, scroll and dimensions. It is the main visual inspection tool.

Executes arbitrary JavaScript in the current page and returns the value (useful to inspect the DOM, read texts, count elements, try selectors).

Runs a YATT (leaf) step in the current page: click, type, hover, assert_*, goto, wait_visible, etc. Returns ok/error, duration and, on failure, an evidence screenshot. With vars it interpolates {{name}} into the step before running it. Structure steps (if/repeat/for_each/run_flow) run with test_run, not here.

Checks whether an element exists in the page (or whether a variable condition holds); waits for the condition with optional polling (timeoutMs > 0 repeats the check until true or the timeout expires). Returns {value, elapsedMs}.

Scrolls the page vertically (dy in pixels, positive moves down) and returns the updated preview.

Click at viewport coordinates (x, y in CSS pixels); returns the resolved selector of the clicked element (data-testid → id → CSS path) plus the updated preview. Prefer browser_run_step with a selector for reproducible steps.

Opens a new tab (optionally with a URL) and returns the tab list.

Lists the open tabs: index, active, title and URL.

Switches to the tab with the given index (0-based).

Closes a tab (by index; without an index closes the active one).

Saves the current session state (cookies/localStorage) under a name, for tests with prior authentication.

Lists the saved sessions.

Deletes a saved session.