From a page problem to repeatable regression
From first principles, a trustworthy interface change must answer three questions.
A3S Test connects those results in one short, checkable loop. The browser supplies current facts. The coding agent chooses one typed action or explicit difference. Core admits it, verification reads the changed page again, and only then does the stable path become ACL.
The shortest trustworthy path
This order matters. A screenshot cannot prove component ownership. A source hint cannot prove the page rendered correctly. Model advice cannot grant edit authority. Each stage contributes one kind of truth and keeps its own boundary.
Choose one entry point
Test Kit is optional for ordinary browser automation. Add it when the task needs component ownership, ranked source spans, rendered geometry, visual evidence, or human marking.
The init, doctor, and dev local project loop is staged on main for the next release. The published v1.0.0 binary predates it. This guide therefore uses the released persistent-session commands below.
Install the CLI and Agent Skill
macOS or Linux
Windows PowerShell
The installer downloads the platform CLI, verifies its SHA-256, and installs the matching Skill for detected coding agents. See Installation to choose only Test Kit, only the CLI, or a specific agent destination.
1. Declare a result the page can prove
Start the local product, then name the goal and an observable success condition.
The session retains its browser, exact-origin policy, and append-only event log until it is explicitly finished, aborted, or timed out.
2. Read the page that actually rendered
The response contains a new observation_id and refs bound to that observation.
Page changes expire @eN, @uN, geometry, and screenshots. An @cN stable locator survives only inside the latest observation when an exact complete delta proves its private node unchanged; every changed, reset, legacy, or uncertain binding expires. This prevents an agent from silently applying an old decision to a new page state.
3. Execute one admitted action
Bind the action to the observation you just read.
Before the driver runs, A3S Test validates the action schema, session capability, target type, origin policy, and observation revision. Continue by observing again, not by reusing the old ref.
4. Verify the changed page and retain evidence
After the success condition appears, save the minimum evidence that another person or agent needs to inspect the result.
events.jsonl explains each admitted step. report.json holds the terminal result. artifacts/ contains only files owned by this session.
5. Preserve only the proven path
Exploration discovers the path. ACL keeps its smallest stable form. Encode explicit actions, bounded waits, assertions, and evidence, then admit the suite before running it.
Continue with Exploration and regression workflows for a complete ACL example. Use Assertions and stability when the success condition depends on control state, rendered text, collections, layout, viewport coverage, pointer reachability, or focus ownership.
Where Test Kit enters
Test Kit derives bounded context after browser rendering. It adds component ownership, stable locator candidates, multi-space geometry, ranked source spans, and a human review surface without replacing the browser accessibility tree.