evals

Stagehand Evals

Agent benchmarks for Stagehand — act, extract, observe, agent, plus dataset-backed suites (WebVoyager, OnlineMind2Web, WebTailBench, Odysseys, HardBench).

Driven by an interactive TUI (evals) or single-shot CLI (evals run …). Tasks are auto-discovered from tasks/bench/<category>/ — no registration step.

Quickstart

From the stagehand repo root:

pnpm install
pnpm build:cli   # also: pnpm build, if you haven't built the workspace yet

This links an evals binary on your PATH. Launch the REPL:

evals

Or run a single target:

evals run extract -t 3 -c 5
evals run b:webvoyager -l 10

A .env in packages/evals/ is loaded automatically. Provide whichever provider keys (OPENAI_API_KEY, ANTHROPIC_API_KEY, GOOGLE_GENERATIVE_AI_API_KEY, …) and BROWSERBASE_API_KEY / BROWSERBASE_PROJECT_ID you need.

TUI commands

Inside the REPL (or as evals <command> from your shell):

Command	What it does
run [target] [options]	Run evals. Target can be a tier, category, task, or benchmark shorthand.
list [tier] [--detailed]	List discovered tasks and categories.
new <tier> <category> <name>	Scaffold a new task file.
config [set|reset|path]	Read or write defaults (env, trials, concurrency, model, …).
experiments	Inspect and compare Braintrust experiment runs.
help	Show command help. Append --help to any command for details.

Use Esc to abort an in-flight run without exiting the REPL.

Onboarding

evals welcome runs a guided first-run flow built on the agent benchmarks: an animated intro (the Stagehand mark, what evals measures, EVALS), then a deterministic replay of a real WebVoyager task — three models in lanes, named generically (Opus, Grok, Sol — the fastest and cheapest fails on a wrong condition filter; timings and costs are illustrative), a podium by accuracy · speed · cost, and a chat-style look inside the winning run. It ends on a real run b:webvoyager -l 3 --harness claude_code -e local (--harness codex when the key is OpenAI's; -e browserbase when that's the available browser) when an Anthropic or OpenAI key and a browser exist, or hands off to evals setup, a guided flow that asks only for what's missing (Anthropic/OpenAI key, browser), writes packages/evals/.env, and offers the first real run.

Set EVALS_WELCOME_WIZARD=1 to auto-run the flow on the first REPL launch; EVALS_NO_WELCOME=1 suppresses the first-run welcome. Any key advances the intro, Esc skips ahead, Ctrl+C cancels.

Run targets

evals run accepts any of these shapes:

Target	Meaning
(none) / all	All bench tasks
bench	Entire bench tier
act / extract / observe / agent	A category
extract/extract_text	A specific task
b:webvoyager / b:onlineMind2Web / b:webtailbench	Dataset-backed benchmark suite

evals list shows everything that's been discovered:

Common options

Flag	Purpose
-e, --env <local|browserbase>	Where the browser runs
-t, --trials <n>	Trials per task
-c, --concurrency <n>	Max parallel sessions
-m, --model <id>	Override the model matrix
--api	Run via the Stagehand API instead of the SDK
--harness <stagehand|claude_code|codex|mastra|pi>	Which agent harness drives the bench task
-l, --limit <n> / -s, --sample <n> / -f, --filter key=value	Suite shaping for benchmark targets
--preview	Print the resolved plan and exit — no browser, no LLM calls

Defaults live in evals.config.json and can be edited via evals config set ….

--preview is useful for sanity-checking the plan before paying for a run:

A live run paints an in-place progress table, then prints a final summary with a per-model breakdown:

Shared harness behavior

See the harness contract for tool surfaces, prompt policy, budget units, session diagnostics, verification, and usage accounting. See HardBench for corpus selection and rubric v1.2.

Adding a bench task

evals new bench extract my_new_task

This drops a defineBenchTask-based file into tasks/bench/extract/. It will show up in evals list on next launch — no config edit needed.

// tasks/bench/extract/my_new_task.ts
import { defineBenchTask } from "../../../framework/defineTask.js";

export default defineBenchTask({
  name: "my_new_task",
  tags: ["regression"],
  run: async ({ stagehand, logger }) => {
    // ... drive stagehand, return { _success: boolean, ... }
  },
});

Tracing / Observability

Runs stream into Braintrust when BRAINTRUST_API_KEY is set; otherwise a local summary prints to stdout. Use evals experiments to inspect and diff past Braintrust runs.