Harness Options

Options

Option	Type	Default	Description
`agentargs`	`AgentArgs`	required	Agent factory — see Agent Interface
`url_override`	`string`	—	Sandbox URL — fetches task dynamically from the backend
`headless`	`boolean`	`true`	Run browser headless
`max_steps`	`number`	`25`	Max actions per task
`viewport`	`object`	`1280x720`	Browser viewport size
`log_level`	`string`	`info`	`debug`, `info`, `warn`, `error`
`verbose`	`boolean`	`false`	Show accessibility tree previews
`grader_endpoint`	`string`	Trayn API	Custom grading endpoint URL
`session_id`	`string`	auto	Session ID override
`run_id`	`string`	auto	Run ID override
`user_id`	`string`	—	User email for run attribution

Usage

When url_override is provided, the harness fetches the task definition from the backend using the session ID embedded in the playground URL.

import { harness } from "@trayn/agent-sdk";
 
const h = harness({
  agentargs: { /* ... */ },
  url_override: "https://app.trayn.ai/playground/{host}/{sessionId}",
});
 
await h.run();

The harness parses the session ID from the URL, fetches the task definition (goal, verifiers, expected actions), and uses it to drive the agent run.

Programmatic Task Editing

Fetch the task definition, modify it, and push changes back to the backend:

import {
  fetchTaskFromUrl,
  pushTaskToRemote,
  parseSessionIdFromUrl,
} from "@trayn/agent-sdk";
 
const playgroundUrl = "https://app.trayn.ai/playground/{host}/{sessionId}";
 
const task = await fetchTaskFromUrl(playgroundUrl);
task.goal = "Updated goal text";
 
const sessionId = parseSessionIdFromUrl(playgroundUrl);
await pushTaskToRemote(sessionId, task);

Task Result

The harness returns a TaskResult for each completed task:

Field	Type	Description
`task_name`	`string`	Task identifier
`success`	`boolean`	Whether the task was completed
`cum_reward`	`number`	Total reward
`n_steps`	`number`	Number of actions taken
`elapsed_time`	`number`	Seconds elapsed
`err_msg`	`string`	Error message if failed

Options

Usage

Programmatic Task Editing

Task Result

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