dsh-browser-playwright

Playwright-powered browser capability for DeepSeek Harness: the agent drives a real browser through accessibility snapshots with stable element refs — no CSS-selector guessing, no full-DOM dumps. One browser session per harness session, tabs, screenshots as durable image attachments, structured extraction, and gated JavaScript evaluation.

Install

dsh plugin --profile <name> add dsh-browser-playwright

The bundle mounts three rows: the ctx.browser seam (service), the Playwright provider (playwright), and the model-facing tool family (tool).

Browser binary

The provider probes chromium → chrome → msedge → edge channels automatically; any installed Chromium-family browser works with zero download. To use Playwright-managed Chromium instead:

npx playwright-core install chromium
# Restricted networks (e.g. mainland China):
PLAYWRIGHT_DOWNLOAD_HOST=https://cdn.npmmirror.com/binaries/playwright npx playwright-core install chromium

Or pin a binary: launch.executablePath / launch.channel in the plugin config.

Tools

The default toolPrefix is browser_. Every action returns a fresh snapshot, so refs always come from the latest result.

Snapshot example

URL: https://example.com/
Title: Example Domain
Refs: 12

- navigation "Main"
  - link "Home" [ref=e1] -> /
  - button "Go" [ref=e2]
- heading "Welcome" [level=1]
- textbox "Search" [ref=e3]

The model then calls browser_click with ref: e2. Invisible content is excluded, node and text caps bound the token cost, and truncation is flagged in the result.

Configuration

All tunables are patchable through the profile's cordis.patch.yml (later layers win per row).

- id: browser
  config:
    provider: playwright                # explicit provider selection

- id: browser-playwright
  config:
    launch:
      channel: chrome                   # or chromium / msedge / edge
      headless: true
      viewport: { width: 1280, height: 800 }
      navigationTimeoutMs: 30000
      ignoreHTTPSErrors: false
    allowedDomains: []                  # e.g. ['github.com'] restricts navigation
    idleTimeoutMs: 600000               # close idle contexts after 10 min; 0 = never
    maxSessions: 8                      # LRU eviction beyond this
    snapshot:
      maxNodes: 500                     # token budget per snapshot tree
      maxNameLength: 120
      maxTextLength: 300

- id: browser-tool
  config:
    toolPrefix: browser_                # model-facing tool name prefix
    allowEvaluate: false                # browser_evaluate gate
    maxWaitMs: 60000                    # browser_wait bound
    extract:
      provider: deepseek-official       # optional: enables browser_extract
      model: deepseek-v4-flash
      maxInputChars: 20000
      maxOutputTokens: 2000

browser_extract needs an auxiliary LLM route (extract.provider + extract.model); without one it fails with an actionable error. browser_evaluate stays off until allowEvaluate: true because it executes arbitrary page JavaScript.

Architecture

A swappable capability seam, one package:

• service — ctx.browser: the provider registry with configured-or-auto selection semantics (a configured id must exist; one usable provider auto-selects; several require an explicit choice).
• playwright — the provider: one shared browser, one BrowserContext per calling session, LRU eviction, idle disposal, URL policy, and the injected snapshot engine.
• tool — the consumer: defineTool-built tools whose canonical values are structured JSON and whose rendered text is the snapshot tree.

Other providers (remote browsers, Browserbase, Steel, …) can register into ctx.browser; the tool schemas stay unchanged. Browser sessions survive across tool calls and keep cookies, storage, and login state within one harness session.

Development

pnpm install
pnpm test          # full suite: engine/action integration on real Chrome, policy, rendering,
                   # schema assembly, plus the realistic scenario suites below
pnpm run build     # tsc → lib/

Test suites

The scenario suites are the plugin's most realistic tests: they drive the browser the way an agent does — snapshot, find a ref, act, re-snapshot — and therefore double as executable documentation of the model experience.

From a DeepSeek Harness source checkout, load this plugin from TypeScript:

pnpm dsh web --patch ./browser-plugin/dev.cordis.yml

Model Experience

Tool schemas

The 17 tool schemas join the system-prompt assembly through ctx.tools.register(); each carries a one-line task-oriented description. Snapshot results are bounded: at most maxNodes nodes, names capped at maxNameLength, and the truncation flag is explicit.

#### Token effect

One tool schema block per tool (small, fixed), plus per-call result text proportional to the visible page, capped by snapshot.maxNodes and name/text limits. Actions return a fresh snapshot, so interactive flows cost roughly one snapshot per step.

#### KV Cache effect

Tool schemas are static per registration and keep the prompt prefix stable. Result content varies with the page, invalidating reuse after each browser tool call, as with any tool result.

Browser state

The page state itself (DOM, cookies, storage) lives in the browser context and never enters the prompt except through snapshot or page-data results.

Known Limitations and Deferred Work

• Selector-free, not vision-free — interaction is a11y-tree based; purely visual widgets (canvas, WebGL, custom-drawn controls) may expose no refs. browser_screenshot + an image-capable model is the fallback.
• Cross-origin iframes appear as leaf (frame) nodes without refs; same-origin frames are walked up to two levels deep.
• Evaluate gate is config, not approval — enabling allowEvaluate trusts the model with arbitrary page JavaScript; compose it with the harness approval/permission policy for stricter control.
• Chromium family only — Firefox/WebKit channels are not probed; providers are swappable if another engine is needed.
• Extract needs a dedicated model route — it does not reuse the main request's route; misconfiguration fails loudly at call time.
• JS-driven navigations are not statically checkable — allowedDomains now covers browser_navigate, browser_open_tab, and link clicks, but a button whose handler runs location.href = … can still leave the allowed hosts; deploy an external network guard for hard isolation.

Ref and lifecycle safety (fixed)

The scenario suites originally surfaced four hazards, now fixed and regression-tested:

• Stale refs fail fast — refs carry a per-snapshot nonce, so after a client-side re-render a stale ref matches nothing and browser_click fails with REF_NOT_FOUND instead of silently acting on a different element.
• Link clicks respect allowedDomains — clicking an in-page link to a disallowed host is rejected with URL_NOT_ALLOWED.
• Idle disposal defers during operations — a navigation slower than idleTimeoutMs completes normally; disposal only fires when the session is truly idle.
• Mid-navigation snapshots settle — a browser_snapshot racing a JS navigation waits for the new document and retries instead of surfacing a raw "Execution context was destroyed" error.

License

MIT