Stably vs BrowserBash: AI QA Agent Comparison 2026

If you are shopping for a Stably AI testing alternative in 2026, you have probably already noticed that "AI QA agent" means two very different things depending on who you ask. To some vendors it means a hosted SaaS that generates, runs, and self-heals an entire Playwright suite in the cloud. To others it means a small command-line agent that drives your own Chrome from a plain-English objective and never phones home. Stably and BrowserBash sit on opposite ends of that spectrum, and which one fits you comes down to three honest questions: how much autonomy you want the agent to have, where your test data is allowed to go, and whether you are willing to pay a per-credit cloud bill or would rather run the model on your own machine for nothing.

This comparison is written for engineers who actually have to pick. I will not invent Stably benchmarks or guess at internals that aren't public. Where a fact isn't on Stably's site or docs as of 2026, I'll say so and move on. The goal is a fair read of two tools that overlap in ambition but diverge sharply in architecture.

What Stably actually is

Stably is an AI-native QA testing platform from a Y Combinator-backed company (the same team behind the Orca open-source editor). The pitch is straightforward: point it at your web app, describe what you want tested in plain English, and the platform auto-generates, runs, and maintains end-to-end tests for you. Stably positions itself as "the AI layer for Playwright" — it generates Playwright tests, runs them in cloud browsers or inside your CI, and uses an LLM (Claude Sonnet is named in their docs for the auto-heal path) to repair tests when selectors drift or the UI changes.

The headline capabilities, per Stably's own marketing and docs as of 2026, are:

• Natural-language test authoring with a no-code visual editor, so non-engineers can create and edit flows.
• AI-generated Playwright scripts you can run in CI/CD, with screenshots, traces, and recordings.
• Auto-heal and caching, so a UI change doesn't immediately turn the suite red — the agent patches the test and keeps it deterministic.
• Parallel cloud browsers and agents for scale.
• Human-in-the-loop hooks when the agent gets stuck.

Pricing is credit-based. As of early 2026 Stably advertises a free tier with $10/month in credits, a Team plan around $60/month, and a Growth plan around $250/month, with capacity scaling by spend. That's a genuine, managed product with a team behind it — and for a lot of companies that's exactly the right shape.

What BrowserBash actually is

BrowserBash is a free, open-source (Apache-2.0) natural-language browser automation CLI built by The Testing Academy, founded by Pramod Dutta. You install it with one command, write a plain-English objective, and an AI agent drives a real Chrome or Chromium browser step by step — no selectors, no page objects, no recorded scripts. It returns a verdict plus structured results. The current release is 1.3.1.

npm install -g browserbash-cli
browserbash run "Log in with the demo account, add the blue running shoes to the cart, complete checkout, and verify the page shows 'Thank you for your order!'"

The defining design choice is that BrowserBash is Ollama-first. Out of the box it defaults to free local models, with no API keys and nothing leaving your machine. It auto-resolves a provider in this order: a local Ollama install, then ANTHROPIC_API_KEY, then OPENROUTER_API_KEY. So if Ollama is running, you get a genuine $0 model bill and full data isolation. If you'd rather use a hosted model for a hard flow, it supports OpenRouter (including genuinely free hosted models like openai/gpt-oss-120b:free) and Anthropic Claude with your own key.

There's no account required to run anything. An optional, free cloud dashboard exists for run history, video recordings, and per-run replay, but it is strictly opt-in — you only touch it if you run browserbash connect and pass --upload. There's also a fully local dashboard (browserbash dashboard) if you want history and replay with zero cloud involvement.

So both tools answer "how do I test a web app with AI instead of brittle selectors?" The split is in where the intelligence runs and who holds your data.

The honest overlap

Before the differences, here's what genuinely carries over between the two, because pretending they're opposites in every dimension wouldn't help you choose:

• Plain-English intent. Both let you describe a flow in natural language instead of writing or maintaining selectors. You say "test checkout with an expired coupon," and the agent figures out the clicks.
• Real browser execution. Both drive actual Chromium-based browsers, not a stripped-down DOM sandbox.
• CI-friendly output. Both produce artifacts you can wire into a pipeline — Stably with cloud traces and recordings, BrowserBash with NDJSON events, exit codes, screenshots, and .webm video.
• Self-healing intent, different mechanisms. Stably has an explicit auto-heal feature that patches committed Playwright tests. BrowserBash doesn't commit selectors at all, so there's nothing to "heal" — the agent re-derives the path from the live page on every run. Different philosophy, same goal of surviving UI churn.

That last point is worth sitting with, because it's the crux of the comparison.

Autonomy: a managed suite vs a stateless agent

Stably's autonomy is suite-level. It wants to own your test estate: generate the tests, store them, run them on a schedule or in CI, watch them go red, and heal them. The promise is "80% coverage in a day with zero code." That's a real value proposition if your bottleneck is that nobody on the team has time to author and babysit a Playwright suite. The agent's job is continuous maintenance of an asset Stably manages for you.

BrowserBash's autonomy is run-level and stateless. Each invocation is an agent driving a browser toward one objective, then exiting with a verdict. It doesn't maintain a persistent suite for you (though you can commit Markdown tests — more on that below). This is a sharper fit when you want an agent you call from your own orchestration: a CI gate, a coding agent verifying its own change, a quick smoke check before a deploy.

# Agent mode: NDJSON on stdout, one JSON event per line, stable exit codes
browserbash run "Open the pricing page and confirm the Pro plan lists a 14-day free trial" --agent --headless

In --agent mode, BrowserBash emits one JSON event per line and uses precise exit codes: 0 passed, 1 failed, 2 error, 3 timeout. Nothing to parse out of prose. That makes it a clean building block for AI coding agents and CI scripts — it's designed to be called by automation rather than to be the automation platform. You can read more about that contract on the features page.

Neither model is strictly better. If you want a system that owns and continuously maintains your coverage, Stably's suite-level autonomy is the point. If you want a deterministic, callable agent you compose yourself, BrowserBash's stateless model is cleaner and has fewer moving parts.

Privacy: cloud-only inference vs local-first

This is the dimension where the two genuinely part ways, and it's the strongest reason teams look for a Stably AI testing alternative in the first place.

Stably is, by design, a cloud product backed by hosted LLMs. Test generation and auto-heal route through a cloud model (Claude, per their docs). That means your application's DOM, page structure, and whatever data is on screen during a run can be sent to a third-party model API. For most marketing sites and internal dashboards, that's a non-issue. But if your test fixtures touch real customer PII, regulated health or financial data, or pre-release features under NDA, "the DOM goes to a cloud LLM" is a compliance conversation, not a footnote. To be fair, Stably can run the actual browser execution inside your own CI, and enterprise data terms may exist that aren't fully public as of 2026 — if you're in a regulated shop, that's a question to put to their sales team directly rather than assume either way.

BrowserBash inverts the default. With Ollama running locally, the model inference happens on your machine, the browser runs on your machine, and nothing — not the DOM, not screenshots, not your objective text — leaves the box. There are no API keys to leak and no third party in the loop. If you need an audit-friendly story, "we can guarantee a $0 model bill and zero data egress on local models" is a clean sentence to put in front of a security reviewer.

There's an honest caveat here, and BrowserBash doesn't hide it: very small local models (roughly 8B parameters and under) can get flaky on long, multi-step objectives — they lose the plot halfway through a checkout flow. The sweet spot for fully-local runs is a mid-size model (Qwen3 or Llama 3.3 70B-class). If you only have a laptop GPU and need a hard flow to pass reliably, the pragmatic move is to point BrowserBash at a capable hosted model just for that run. The privacy/cost win is real, but it scales with the hardware you have.

Cost: per-credit cloud bill vs $0 on local

Cost is where the architectural difference turns into a number on an invoice.

With Stably you're buying capacity. Credits get consumed by generation, runs, and healing, and heavy suites cost more — that's the model, and it's predictable in the way SaaS is predictable. With BrowserBash on local models, the marginal cost of a run is electricity. The trade is that you're responsible for the hardware and for choosing a model that's actually good enough for your flows. If you switch BrowserBash to a hosted model for a hard run, you pay that provider's token rate (and OpenRouter has free hosted tiers that keep even that at $0 for many cases). You can see how the free/opt-in split works on the pricing page.

A blunt way to think about it: Stably is cheaper in engineering hours if you have none to spare, because it does authoring and maintenance for you. BrowserBash is cheaper in dollars and data risk because the default path costs nothing and ships nothing off your machine. Those aren't the same axis, and which one dominates depends entirely on your constraints.

Test artifacts and the committable-test story

Both tools care about producing evidence, but the shape differs.

Stably gives you cloud traces, recordings, and screenshots tied to runs in its dashboard, and it generates real Playwright code you can in principle take with you — a meaningful hedge against lock-in, since a Playwright file is a Playwright file.

BrowserBash leans into local, committable artifacts. It supports Markdown tests: plain *_test.md files where each list item is a step, with @import for composing shared flows and {{variables}} for templating. Variables marked as secrets are masked as ***** in every log line, which matters when a step needs a password or token.

browserbash testmd run ./checkout_test.md

A test file might read like this, with a secret variable that never appears in plaintext logs:

# checkout_test.md
- Go to {{baseUrl}}
- Log in as {{username}} with password {{password}}   # password is secret-marked, masked as *****
- Add "Blue Running Shoes" to the cart
- Complete checkout
- Verify the page shows "Thank you for your order!"

After every run BrowserBash writes a human-readable Result.md. For richer evidence, --record captures a screenshot and a full .webm session video via ffmpeg on any engine; the builtin engine additionally captures a Playwright trace you can open in the trace viewer.

browserbash run "Sign up for a trial and confirm the welcome email banner appears" --record --upload

The mental model difference: Stably's artifacts live in its cloud by default; BrowserBash's live in your repo and your filesystem, with the cloud strictly optional. If you want test definitions in Git, reviewed in pull requests, and diffed like code, BrowserBash's *_test.md format is the more natural fit. If you want a managed dashboard as the source of truth, Stably's model is built for that.

Where the browser runs

One more axis that often gets overlooked: execution location.

BrowserBash uses your local Chrome by default but switches execution targets with a single --provider flag. It supports local (your Chrome), cdp (any DevTools endpoint), and the major cloud grids — browserbase, lambdatest, and browserstack. So you can develop locally and private, then fan the same objective out to a cloud grid for cross-browser coverage without rewriting anything.

browserbash run "Verify the cookie banner appears and can be dismissed" --provider lambdatest

Under the hood, BrowserBash offers two engines: stagehand (the default, MIT-licensed, from Browserbase) and builtin (an in-repo Anthropic tool-use loop). The builtin engine is the one that adds the Playwright trace on --record.

Stably runs in its own cloud browsers or inside your CI. It's less about "bring your own browser provider" and more about "we run the browsers, you consume the results." For teams that don't want to think about browser infrastructure at all, that's a feature, not a limitation. For teams that already have a BrowserStack or LambdaTest contract and want to keep using it, BrowserBash's provider flag is the more flexible path.

When to choose Stably

Be honest with yourself about your constraints. Stably is the better pick when:

• You want a managed test suite and have little or no engineering time to author and maintain one. The "80% coverage in a day" pitch is aimed squarely at you.
• Non-engineers need to create and edit tests. The no-code visual editor is a real advantage for QA analysts, PMs, and support engineers who won't be writing CLI commands.
• You want auto-heal on a committed suite so UI churn doesn't constantly break a large, long-lived test estate.
• Cloud-hosted inference and browsers are acceptable in your environment, and a per-credit bill is an easier sell than provisioning hardware.
• You'd rather buy a finished product with support than assemble an agent into your own pipeline.

If those describe your team, the managed SaaS model earns its price, and BrowserBash would be more assembly than you want.

When to choose BrowserBash

BrowserBash is the stronger Stably alternative when:

• Data can't leave your machine. Local Ollama execution means zero DOM/screenshot egress and no cloud LLM in the loop — the cleanest answer to a security reviewer.
• You want a genuine $0 model bill. Default local models cost nothing per run; hosted models are optional and there are free OpenRouter tiers.
• No account, no signup. npm install -g browserbash-cli and you're running in under a minute, which matters for spinning up smoke tests fast or for environments where account provisioning is friction.
• You're wiring an agent into automation. NDJSON output, clean exit codes (0/1/2/3), and --agent mode make it a building block for CI gates and AI coding agents, not a destination dashboard.
• You want tests in Git. Committable *_test.md files with @import, {{variables}}, and secret masking live alongside your code and get reviewed in PRs.
• You already have a cloud grid. The --provider flag fans the same objective out to Browserbase, LambdaTest, or BrowserStack without a rewrite.

The honest caveat applies: on small local models, hard multi-step flows can wobble, so plan for a mid-size local model or a hosted model on the difficult runs. If you can live with that, the privacy and cost story is hard to beat. There's a worked example on the case study page if you want to see a real flow end to end.

The bottom line

Stably and BrowserBash aren't really competing for the same slot in your stack. Stably is a managed AI QA platform that owns and maintains a suite for you, billed by credits, running in the cloud. BrowserBash is a free, local-first AI agent you call from the command line, with nothing leaving your machine by default. If your pain is "we have no test coverage and no time to build it," Stably's autonomy and no-code authoring are worth paying for. If your pain is "we can't send our DOM to a cloud model" or "we want a free, scriptable agent in CI," BrowserBash is the better tool, and it costs nothing to find out.

The good news: BrowserBash is free to try, so you can run a real flow against your own app this afternoon and compare the output yourself. Browse the BrowserBash blog for more head-to-head breakdowns.

FAQ

Is BrowserBash a free alternative to Stably AI?

Yes. BrowserBash is free and open source under Apache-2.0, with no account required to run it. On local Ollama models the model bill is genuinely $0 and nothing leaves your machine, whereas Stably is a credit-based cloud SaaS starting with a free tier and paid Team and Growth plans. The trade-off is that BrowserBash is a callable agent rather than a managed test-suite platform.

Does BrowserBash send my test data to the cloud like Stably?

No, not by default. With a local Ollama model, both the AI inference and the browser run on your own machine, so the DOM, screenshots, and your objective text never leave the box. A cloud dashboard exists but is strictly opt-in via browserbash connect and the --upload flag, and there is also a fully local dashboard. Stably, by contrast, routes test generation and auto-heal through a hosted cloud LLM.

Can BrowserBash generate and maintain a Playwright suite the way Stably does?

Not in the same way. Stably auto-generates and self-heals a committed Playwright test estate, which is its core value. BrowserBash doesn't commit selectors at all — it re-derives the path from the live page on every run from your plain-English objective, and it supports committable Markdown tests with variables and secret masking. If you specifically want a managed Playwright suite with auto-heal, Stably is the better fit.

Which is better for CI and AI coding agents, Stably or BrowserBash?

It depends on whether you want a platform or a building block. BrowserBash is built to be called from automation: --agent mode emits NDJSON, exit codes are precise (0 passed, 1 failed, 2 error, 3 timeout), and it produces local screenshots, videos, and traces. Stably is built to own and run your suite in its own cloud or your CI with a dashboard as the source of truth, which suits teams that want a finished product over a composable agent.

Ready to try a private, local-first AI QA agent? Install it with npm install -g browserbash-cli and run your first plain-English flow in minutes — no account needed, though a free dashboard is available at browserbash.com/sign-up if you want run history and replay later.