Antithesis agent-browser

Skill version: 2026-09-23 a8fe900

A helper skill for reading data from authenticated Antithesis web pages when the snouty API doesn't expose what's needed. Other skills (antithesis-triage, antithesis-debug, antithesis-query-logs) delegate here when they need an authenticated browser session.

Purpose

• Handle interactive authentication to the user's Antithesis tenant with minimal disruption.
• Load Antithesis web pages (reports, logs, runs, causality) and extract data from them via an injected runtime.

When to use

• When another skill needs information from an Antithesis page that snouty cannot reliably provide.
• When the user or another skill needs to interact with an Antithesis web page directly.

Prerequisites

• DO NOT PROCEED if agent-browser is not installed. See https://raw.githubusercontent.com/vercel-labs/agent-browser/refs/heads/main/README.md for installation options.
• DO NOT PROCEED if agent-browser is older than version v0.23.4. You can upgrade with agent-browser upgrade.
• DO NOT PROCEED if jq is not installed. See https://jqlang.org/download/ for installation options.

Reference files: This skill's references/ directory contains detailed guides for specific tasks. Do NOT read them all up front — only read a reference file when you are told to. Each reference file is mentioned by name at the point where it is needed.

General guidance

• Always ensure you are authenticated first.
• Use disposable sessions. Generate a unique SESSION for each invocation of this skill.
• Inject the runtime after navigation. After every open, after link clicks that may change pages, and after reopening a report from a finding route, wait until networkidle, inject assets/antithesis-agent-browser.js, then use the matching *.waitForReady() method before continuing.
• Never run agent-browser calls in parallel. They are stateful with side effects.
• Retry missing-runtime errors by reinjecting. If a command fails because window.__antithesisAgentBrowser is undefined or missing, inject the runtime and rerun the same method.
• Keep report evals on the main report view. If you click into another page by accident, reopen the original report URL before using report queries again.

Session management with agent-browser

agent-browser has two session variables:

• --session: the name of a unique, isolated browser instance
• --session-name: auto-save/restore cookies by name

Every invocation MUST use a unique --session value. Generate it once and reuse it whenever you see $SESSION referenced by this skill.

SESSION=antithesis-ab-$(date +%s)-$$

Use --session-name antithesis on the FIRST agent-browser command that references a new $SESSION. This creates the session and restores saved cookies. Subsequent commands for the same $SESSION do not need --session-name — the session already exists.

Close the live session when done.

agent-browser --session $SESSION close

Authentication

Do NOT navigate to the home page just to check auth. Instead, navigate directly to your target URL (report, runs page, etc.) using the session-creation command:

agent-browser --session "$SESSION" --session-name antithesis open "$TARGET_URL"
agent-browser --session "$SESSION" wait --load networkidle
agent-browser --session "$SESSION" get url

If the URL starts with https://$TENANT.antithesis.com then you are authenticated. If it redirected to a login page, you need to authenticate — read references/setup-auth.md, which gates the interactive headed login on user confirmation.

Runtime injection

This skill ships a runtime (assets/antithesis-agent-browser.js) that exposes helper methods on window.__antithesisAgentBrowser for reading data from Antithesis pages. Inject it after navigation completes:

cat assets/antithesis-agent-browser.js \
  | agent-browser --session "$SESSION" eval --stdin

Call its methods with agent-browser eval:

agent-browser --session "$SESSION" eval \
  "window.__antithesisAgentBrowser.report.getRunMetadata()"

agent-browser eval awaits Promises automatically, so async and sync methods use the same call pattern.

Error handling: Runtime methods throw on error, which causes agent-browser eval to return a non-zero exit code. Check the exit code to detect failures — no output parsing required. The error message describes what went wrong (e.g. wrong page, element not found, timeout).

If window.__antithesisAgentBrowser is missing, reinject assets/antithesis-agent-browser.js and retry.

NEVER run agent-browser calls in parallel. They are stateful calls with side effects; parallel calls can break or return confusing results.

Navigation and loading

Each Antithesis page loads content asynchronously. After navigation to any Antithesis page, follow this pattern:

First, wait for networkidle:

agent-browser --session "$SESSION" wait --load networkidle

Then, check the url to see if you got redirected to an authentication page:

agent-browser --session "$SESSION" get url

If you hit an authentication page, stop and reauthenticate before continuing.

Then, inject the runtime:

cat assets/antithesis-agent-browser.js \
  | agent-browser --session "$SESSION" eval --stdin

Finally, eval the page-specific wait function to wait for all asynchronous chunks to finish loading:

• Report page: window.__antithesisAgentBrowser.report.waitForReady()
• Logs page: window.__antithesisAgentBrowser.logs.waitForReady()
• Runs page: window.__antithesisAgentBrowser.runs.waitForReady()

Each wait method polls for up to 60 seconds by default. On success it returns { attempts, waitedMs }. On timeout, the method throws causing agent-browser eval to return a non-zero exit code.

Use the lower-level boolean checks when you need a one-shot probe:

• Report page: window.__antithesisAgentBrowser.report.loadingFinished()
• Logs page: window.__antithesisAgentBrowser.logs.loadingFinished()
• Runs page: window.__antithesisAgentBrowser.runs.loadingFinished()

If a page still does not become ready, inspect status:

• Report page: window.__antithesisAgentBrowser.report.loadingStatus()
• Logs page: window.__antithesisAgentBrowser.logs.loadingStatus()
• Runs page: window.__antithesisAgentBrowser.runs.loadingStatus()

Handling error reports

After every report waitForReady() call, check result.error. If it is present, read references/error-reports.md for the error-report workflow.

What this skill can do

1. Authenticate to the tenant. Read references/setup-auth.md for the interactive login flow.
2. Discover runs from the runs page. Read references/run-discovery-ui.md. Prefer snouty runs list whenever possible — only fall back to the UI when the API is unavailable or doesn't expose what you need.
3. Read properties from a triage report. Read references/properties-from-ui.md. Prefer snouty runs --json properties whenever possible.
4. Look up a run_id from a triage-report URL that cannot be matched against snouty runs list. The run_id is rendered at the bottom of the main report page (report_id → run_id is not currently exposed by the API).
5. Download an error log from a failed run's report page. See references/error-reports.md.
6. Read a causality report. Ask the user for the causality report URL. The main signal is the bug-probability trajectory in the logs leading up to the bug moment.