Next Browser

Onboarding

• If the user already gave a URL, cookies, and task — skip questions, open and go.
• Otherwise ask only what's missing: dev server URL (running?), session cookies if behind login.
• For cookies, give the user two options: (1) DevTools → Application → Cookies, export as [{"name":"session","value":"..."}], or (2) just "Copy as cURL" from DevTools → Network on any authenticated request — you can extract the cookies from the header yourself.
• Never say "ready, what would you like to do?". Never auto-discover (port scans, project, config reads) before being asked.

Show, don't tell

• screenshot after every navigation, code change, or visual finding. Always caption it (screenshot "Before fix", screenshot "PPR shell — locked"). In headed mode the Screenshot Log window opens automatically so the user sees every screenshot in real time.
• Don't narrate what a screenshot shows. State your conclusion or next action.

Escalate, don't decide

• Suspense boundary placement and fallback UI — design with the user.
• Caching decisions (staleness, visibility) — the user's call, not yours.
• "Make this page faster" without context — ask: cold URL hit or client navigation? From which page? Don't guess, don't do both.

Headless mode

By default the browser opens headed (visible window). For CI or cloud environments with no display, set NEXT_BROWSER_HEADLESS=1 to run headless.

Commands

open <url> [--cookies-json <file>]

Launch browser, navigate to URL. With --cookies-json, sets auth cookies before navigating (domain derived from URL hostname).

$ next-browser open http://localhost:3024/vercel --cookies-json cookies.json
opened → http://localhost:3024/vercel (11 cookies for localhost)

Cookie file format: [{"name":"authorization","value":"Bearer ..."}, ...]

Only name and value are required per cookie — omit domain, path, expires, etc. To create the file, use Bash (echo '[...]' > /tmp/cookies.json) since the Write tool requires a prior Read.

close

Close browser and kill daemon.

goto <url>

Navigate to a URL with a fresh server render. The browser loads a new document — equivalent to typing a URL in the address bar.

$ next-browser goto http://localhost:3024/vercel/~/deployments
→ http://localhost:3024/vercel/~/deployments

push [path]

Client-side navigation — the page transitions without a full reload, the way a user clicks a link in the app. Without a path, shows an interactive picker of all links on the current page.

$ next-browser push /vercel/~/deployments
→ http://localhost:3024/vercel/~/deployments

If push fails silently (URL unchanged), the route wasn't prefetched.

back

Go back one page in browser history.

reload

Reload the current page from the server.

ssr lock

Block external scripts on all subsequent navigations. While locked, every goto, push, back, and reload shows the raw server-rendered HTML without React hydration or client-side JavaScript — what search engines and social crawlers see.

$ next-browser ssr lock
ssr locked — external scripts blocked on all navigations

ssr unlock

Re-enable external scripts. The next navigation will load normally with full hydration.

$ next-browser ssr unlock
ssr unlocked — external scripts re-enabled

perf [url]

Profile a full page load — reloads the current page (or navigates to a URL) and collects Core Web Vitals and React hydration timing in one pass.

$ next-browser perf http://localhost:3000/dashboard
# Page Load Profile — http://localhost:3000/dashboard

## Core Web Vitals
  TTFB                   42ms
  LCP               1205.3ms (img: /_next/image?url=...)
  CLS                    0.03

## React Hydration — 65.5ms (466.2ms → 531.7ms)
  Hydrated                         65.5ms  (466.2 → 531.7)
  Commit                            2.0ms  (531.7 → 533.7)
  Waiting for Paint                 3.0ms  (533.7 → 536.7)
  Remaining Effects                 4.1ms  (536.7 → 540.8)

## Hydrated components (42 total, sorted by duration)
  DeploymentsProvider                       8.3ms
  NavigationProvider                        5.1ms
  ...

TTFB — server response time (Navigation Timing API). LCP — when the largest visible element painted, plus what it was. CLS — cumulative layout shift score (lower is better). Hydration — React reconciler phases and per-component cost (requires React profiling build / next dev; production strips console.timeStamp).

Without a URL, reloads the current page. With a URL, navigates there first.

renders start

Begin recording React re-renders. Hooks into onCommitFiberRoot to collect raw per-component data: render count, totalTime, selfTime, DOM mutations, change reasons, and FPS.

Survives full-page navigations (goto/reload) and captures mount and hydration renders — no need to start before or after navigation.

$ next-browser renders start
recording renders — interact with the page, then run `renders stop`

renders stop [--json]

Stop recording and print a per-component render profile. Raw data — the agent decides what's actionable.

$ next-browser renders stop
# Render Profile — 3.05s recording
# 426 renders (38 mounts + 388 re-renders) across 38 components
# FPS: avg 120, min 106, max 137, drops (<30fps): 0

## Components by total render time
| Component              | Insts | Mounts | Re-renders | Total    | Self     | DOM   | Top change reason          |
| ---------------------- | ----- | ------ | ---------- | -------- | -------- | ----- | -------------------------- |
| Parent                 |     1 |      1 |          9 |   5.8ms  |   3.4ms  | 10/10 | state (hook #0)            |
| MemoChild              |     3 |      3 |         27 |     2ms  |   1.9ms  | 30/30 | props.data                 |
| Router                 |     1 |      1 |          9 |   6.3ms  |       —  |  0/10 | parent (ErrorBoundaryHandler) |

## Change details (prev → next)
  Parent
    state (hook #0): 0 → 1
  MemoChild
    props.data: {value} → {value}

The Change details section shows the actual prev→next values for each change. This makes the data self-contained — you can see that MemoChild gets props.data: {value} → {value} (same shape, new reference — memo defeated) without needing to inspect the component.

With --json, outputs raw structured JSON with full change arrays per component (type, name, prev, next for each render event).

Columns:

• Insts — number of unique component instances observed during recording
• Mounts — how many times an instance mounted (first render, no alternate fiber)
• Re-renders — update-phase renders (total renders minus mounts)
• Total — inclusive render time (component + children)
• Self — exclusive render time (component only, excludes children)
• DOM — how many renders actually mutated the DOM vs total renders
• Top change reason — most frequent trigger for this component

Timing data (Total, Self) requires a React profiling build (next dev). In production builds these columns show — but render counts, DOM mutations, and change reasons are still reported.

Change reasons — what triggered each re-render:

• props.<name> — a prop changed by reference, with prev→next values
• state (hook #N) — a useState/useReducer hook changed, with prev→next values
• context (<name>) — a specific context changed, with prev→next values
• parent (<name>) — parent component re-rendered, names the parent
• parent (<name> (mount)) — parent is also mounting (typical during page load, not a leak)
• mount — first render

FPS — frames per second during recording. drops counts frames below 30fps.

Up to 200 components are tracked. If output exceeds 4 000 chars it is written to a temp file.

restart-server

Restart the Next.js dev server and clear its caches. Forces a clean recompile from scratch.

Last resort. HMR picks up code changes on its own — reach for this only when you have evidence the dev server is wedged (stale output after edits, builds that never finish, errors that don't clear).

Often exits with net::ERR_ABORTED — this is expected (the page detaches during restart). Follow up with goto <url> to re-navigate after the server is back. Don't treat this error as a failure.

ppr lock

Prerequisite: PPR requires cacheComponents to be enabled in next.config. Without it the shell won't have pre-rendered content to show.

Freeze dynamic content so you can inspect the static shell — the part of the page that's instantly available before any data loads. After locking:

• goto — shows the server-rendered shell with holes where dynamic content would appear.
• push — shows what the client already has from prefetching. Requires the current page to already be hydrated (prefetch is client-side), so lock after you've landed on the origin, not before.

$ next-browser ppr lock
locked

ppr unlock

Resume dynamic content and print a shell analysis — which Suspense boundaries were holes in the shell, what blocked them, and which were static. The output can be very large (hundreds of boundaries). Pipe through | head -20 if you only need the summary and dynamic holes.

$ next-browser ppr unlock
unlocked

# PPR Shell Analysis
# 131 boundaries: 3 dynamic holes, 128 static

## Summary
- Top actionable hole: TrackedSuspense — usePathname (client-hook)
- Suggested next step: This route segment is suspending on client hooks. Check loading.tsx first...
- Most common root cause: usePathname (client-hook) affecting 1 boundary

## Quick Reference
| Boundary                   | Type              | Fallback source | Primary blocker           | Source                        | Suggested next step       |
| ---                        | ---               | ---             | ---                       | ---                           | ---                       |
| TrackedSuspense            | component         | unknown         | usePathname (client-hook) | tracked-suspense.js:6         | Push the hook-using cl... |
| TeamDeploymentsLayout      | route-segment     | unknown         | unknown                   | layout.tsx:37                 | Inspect the nearest us... |
| Next.Metadata              | component         | unknown         | unknown                   | unknown                       | No primary blocker was... |

## Detail
  TrackedSuspense
    rendered by: TrackedSuspense > RootLayout > AppLayout
    environments: SSR
  TeamDeploymentsLayout
    suspenders unknown: thrown Promise (library using throw instead of use())

## Static (pre-rendered in shell)
  GeistProvider at .../geist-provider.tsx:80:9
  TrackedSuspense at ...
  ...

The Quick Reference table is the main overview — boundary, blocker, source, and suggested fix at a glance. The Detail section only appears for holes that have extra info (owner chains, environments, secondary blockers) not already in the table.

errors doesn't report while locked. If the shell looks wrong (empty, bailed to CSR), unlock and goto the page normally, then run errors. Don't debug blind under the lock.

Full bailout (scrollHeight = 0). When PPR bails out completely, unlock returns just "unlocked" with no shell analysis — there are no boundaries to report. In this case, unlock, goto the page normally, then use errors and logs to find the root cause.

tree

Full React component tree — every component on the page with its hierarchy, like the Components panel in React DevTools.

$ next-browser tree
# React component tree
# Columns: depth id parent name [key=...]
# Use `tree <id>` for props/hooks/state. IDs valid until next navigation.

0 38167 - Root
1 38168 38167 HeadManagerContext.Provider
2 38169 38168 Root
...
224 46375 46374 DeploymentsProvider
226 46506 46376 DeploymentsTable

tree <id>

Inspect one component: ancestor path, props, hooks, state, source location (source-mapped to original file).

$ next-browser tree 46375