HUD Documentation — Evaluations and RL Environments.

The HUD SDK provides the Task class for defining agent objectives and dataset utilities for managing task collections.

Task Class

from hud.datasets import Task

Pydantic model that defines an agent’s objective, setup, and evaluation criteria. Fields:

Field	Type	Description	Default
`id`	`str \| None`	Unique identifier (UUID recommended)	`None`
`prompt`	`str`	Task instruction for the agent	Required
`mcp_config`	`dict[str, Any]`	MCP server configuration	Required
`setup_tool`	`MCPToolCall \| list[MCPToolCall] \| None`	Tool(s) to prepare environment	`None`
`evaluate_tool`	`MCPToolCall \| list[MCPToolCall] \| None`	Tool(s) to score performance	`None`
`agent_config`	`dict[str, Any] \| None`	Agent configuration (system_prompt, allowed_tools, etc.)	`None`
`metadata`	`dict[str, Any]`	Extra task metadata	`{}`

Environment Variable Substitution

The mcp_config field automatically resolves environment variables using ${VAR_NAME} syntax:

task = Task(
    prompt="Navigate to the dashboard",
    mcp_config={
        "browser": {
            "url": "${HUD_MCP_URL:https://mcp.hud.ai/v3/mcp}",
            "headers": {
                "Authorization": "Bearer ${HUD_API_KEY}",
                "Mcp-Image": "hudpython/hud-browser:latest"
            }
        }
    }
)

Substitution happens automatically when Task is created from a dict - environment variables are resolved using Python’s Template.substitute() with a defaultdict that returns empty strings for missing variables.

Field Validators

Task automatically:

Parses JSON strings - mcp_config and metadata can be JSON strings
Converts dicts to MCPToolCall - setup_tool and evaluate_tool dicts are converted
Resolves environment variables - Only when created from dict (preserves templates in model_dump())

# All of these work:
task = Task(
    prompt="Test",
    mcp_config='{"server": {"url": "..."}}',  # JSON string → dict
    setup_tool='{"name": "setup"}'            # JSON string → MCPToolCall
)

task = Task(
    prompt="Test", 
    mcp_config={...},
    setup_tool={"name": "setup", "arguments": {...}}  # dict → MCPToolCall
)

task = Task(
    prompt="Test",
    mcp_config={...},
    evaluate_tool=[  # List of tool calls
        {"name": "check_text", "arguments": {"text": "Success"}},
        {"name": "check_url", "arguments": {"url": "example.com"}}
    ]
)

Recommended Evaluation Workflow

When developing and testing agents, follow this progression for optimal debugging and performance:

Step 1: Single Task Development

Start with individual tasks to debug your agent and environment setup:

import hud
from hud.agents import ClaudeAgent
from hud.datasets import Task

task = Task(prompt="Click the submit button", mcp_config={...})

async with hud.async_trace(task.prompt):
    agent = ClaudeAgent()
    result = await agent.run(task, max_steps=50)
    print(f"Result: {result.reward}")

Benefits:

Full error stack traces
Clear log output
Quick iteration cycle
Automatic telemetry tracking

Step 2: Full Dataset Evaluation

Once single tasks work reliably, scale up to full dataset evaluation:

from hud.datasets import run_dataset
from hud.agents import ClaudeAgent

results = await run_dataset(
    name="SheetBench Evaluation",
    dataset="hud-evals/SheetBench-50",
    agent_class=ClaudeAgent,
    agent_config={"model": "claude-sonnet-4-5-20250929", "validate_api_key": False},
    max_concurrent=50,
    max_steps=50,
    auto_respond=True
)

Concurrency Guidelines:

Start with max_concurrent=50 and adjust based on results
Increase to 100-200 for faster evaluation (if API limits allow)
Decrease to 10-20 if hitting rate limits

Quick Reference

Stage	Method	Concurrency	Use Case	Debugging
Development	Single task	1	Initial debugging	Excellent
Production	`run_dataset`	50-200	Full evaluation	Good

Dataset Functions

run_dataset

from hud.datasets import run_dataset
from hud.agents import ClaudeAgent

results = await run_dataset(
    name="SheetBench Evaluation",
    dataset="hud-evals/SheetBench-50",
    agent_class=ClaudeAgent,
    agent_config={"model": "claude-sonnet-4-5-20250929", "validate_api_key": False},
    max_concurrent=50,
    max_steps=50,
    auto_respond=True
)

Parameters:

Parameter	Type	Description	Default
`name`	`str`	Job name for tracking	Required
`dataset`	`str \| Dataset \| list[dict]`	HF dataset ID, Dataset object, or task dicts	Required
`agent_class`	`type[MCPAgent]`	Agent class to instantiate	Required
`agent_config`	`dict[str, Any] \| None`	Constructor kwargs for agent	`None`
`max_concurrent`	`int`	Maximum concurrent tasks (recommended: 50-200)	`30`
`max_steps`	`int`	Max steps per task	`10`
`auto_respond`	`bool`	Use ResponseAgent for continuations	`False`
`metadata`	`dict[str, Any] \| None`	Job metadata	`None`
`split`	`str`	Dataset split when loading by ID	`"train"`

Returns: list[Any] - Results in dataset order Examples:

from hud.datasets import run_dataset
from hud.agents import ClaudeAgent, OperatorAgent

# From HuggingFace dataset
results = await run_dataset(
    "Eval", "hud-evals/SheetBench-50", ClaudeAgent,
    {"model": "claude-sonnet-4-5-20250929"}, max_concurrent=50
)

# From Dataset object  
from datasets import load_dataset
dataset = load_dataset("hud-evals/OSWorld-Verified", split="train")
results = await run_dataset("Eval", dataset, OperatorAgent)

# From list of dicts
tasks = [{"prompt": "...", "mcp_config": {...}, "setup_tool": {...}}]
results = await run_dataset("Eval", tasks, ClaudeAgent)

fetch_system_prompt_from_dataset

from hud.datasets import fetch_system_prompt_from_dataset

system_prompt = await fetch_system_prompt_from_dataset("hud-evals/SheetBench-50")

Fetch system_prompt.txt from a HuggingFace dataset repository. Returns: str | None - System prompt text if found Note: Requires huggingface_hub to be installed.

save_tasks

from hud.datasets import save_tasks

# IMPORTANT: Pass dicts, not Task objects!
task_dicts = [task.model_dump() for task in tasks]
save_tasks(
    tasks=task_dicts,
    repo_id="my-org/my-tasks",
    private=False,
    dataset_name="My Tasks v1.0"
)

Save tasks to HuggingFace dataset with JSON string serialization. Parameters:

Parameter	Type	Description	Default
`tasks`	`list[dict[str, Any]]`	Task dictionaries (NOT Task objects)	Required
`repo_id`	`str`	HuggingFace repository ID	Required
`**kwargs`	`Any`	Additional args for `push_to_hub()`	-

Important: Always pass dictionaries to preserve environment variable templates:

# ✅ GOOD - Preserves ${HUD_API_KEY} in the dataset
task_dicts = [task.model_dump() for task in tasks]
save_tasks(task_dicts, "my-dataset")

# ❌ BAD - Would expose resolved API keys!
# save_tasks(tasks, "my-dataset")  # Don't do this!

Dataset Schema: The function converts complex fields to JSON strings for clean HuggingFace schema:

mcp_config → JSON string
setup_tool → JSON string (if present)
evaluate_tool → JSON string (if present)
metadata → JSON string (if present)

MCPToolCall Type

from hud.types import MCPToolCall

Defines a tool invocation with arguments. Fields:

Field	Type	Description	Default
`name`	`str`	Tool name to call	Required
`arguments`	`dict[str, Any]`	Tool arguments	`{}`

Real-World Examples

Loading Tasks from Datasets

From examples/run_evaluation.py:

# Load dataset
dataset = load_dataset("hud-evals/SheetBench-50", split="train")

# Get system prompt
dataset_system_prompt = await fetch_system_prompt_from_dataset("hud-evals/SheetBench-50")

# Run single task
sample_task = dataset[0]
task = Task(**sample_task)  # Auto-converts dict to Task

# Or run all tasks
results = await run_dataset(
    "Full SheetBench Evaluation",
    dataset,
    ClaudeAgent,
    {"model": "claude-3-5-sonnet-20241022"},
    max_concurrent=50
)

Task Structure in Datasets

From environments/text_2048/2048_taskconfigs.json:

{
    "id": "2048_target_256",
    "prompt": "You are playing 2048 and your goal is to reach the 256 tile.",
    "mcp_config": {
        "local": {
            "command": "docker",
            "args": ["run", "--rm", "-i", "hud-text-2048"]
        }
    },
    "setup_tool": {
        "name": "setup",
        "arguments": {
            "name": "board",
            "arguments": {"board_size": 4}
        }
    },
    "evaluate_tool": {
        "name": "evaluate", 
        "arguments": {
            "name": "max_number",
            "arguments": {"target": 256}
        }
    },
    "metadata": {
        "difficulty": 256,
        "game": "2048"
    }
}

Creating and Saving Tasks

import os
from uuid import uuid4

# Set environment variables
os.environ["HUD_API_KEY"] = "sk-hud-..."
os.environ["BROWSER_PROVIDER"] = "anchorbrowser"

# Create tasks with env var templates
tasks = []
for url in ["example.com", "test.com"]:
    task = Task(
        id=str(uuid4()),
        prompt=f"Navigate to {url} and find the login button",
        mcp_config={
            "browser": {
                "url": "${HUD_MCP_URL:https://mcp.hud.ai/v3/mcp}",
                "headers": {
                    "Authorization": "Bearer ${HUD_API_KEY}",
                    "X-Provider": "${BROWSER_PROVIDER}"
                }
            }
        },
        setup_tool=MCPToolCall(
            name="setup",
            arguments={"name": "navigate", "arguments": {"url": url}}
        ),
        evaluate_tool=MCPToolCall(
            name="evaluate", 
            arguments={"name": "element_exists", "arguments": {"selector": "button.login"}}
        ),
        metadata={
            "category": "navigation",
            "difficulty": "easy"
        }
    )
    tasks.append(task)

# Save to HuggingFace (preserves env var templates)
task_dicts = [t.model_dump() for t in tasks]
save_tasks(task_dicts, "my-org/navigation-tasks")

Agent Integration

Tasks automatically configure agents:

task = Task(
    prompt="Complete the form",
    mcp_config={...},
    setup_tool={...},
    evaluate_tool={...},
    agent_config={
        "system_prompt": "Be very careful with form fields",
        "allowed_tools": ["computer", "search"],
        "append_setup_output": True
    }
)

agent = ClaudeAgent()

# When agent.run(task) is called:
# 1. If no mcp_client, creates one from task.mcp_config
# 2. Applies task.agent_config to agent (system_prompt, allowed_tools, etc.)
# 3. Adds lifecycle tools to agent.lifecycle_tools
# 4. Runs setup_tool (hidden from agent)
# 5. Executes task.prompt
# 6. Runs evaluate_tool (hidden from agent)
# 7. Returns Trace with evaluation reward

Agent Config Options

The agent_config field supports the following options:

Option	Type	Description
`system_prompt`	`str`	Custom system prompt appended to agent’s default
`allowed_tools`	`list[str]`	Tools the agent can use (replaces `agent_tools`)
`disallowed_tools`	`list[str]`	Tools to exclude from the agent
`append_setup_output`	`bool`	Include setup output in first message (default: True)
`initial_screenshot`	`bool`	Take screenshot before first action (default: True)

Best Practices

Use UUIDs for task IDs - Required for HuggingFace datasets
Save dictionaries, not objects - Preserves env var templates
Use agent_config for agent settings - Centralize agent configuration in one place
Use metadata for filtering - Category, difficulty, tags
Test locally first - Before uploading to HuggingFace
Version your datasets - Use meaningful repo names

Common Patterns

Filtering Tasks

# Load all tasks
dataset = load_dataset("hud-evals/WebArena-Lite", split="train")

# Filter in Python
login_tasks = [
    task for task in dataset
    if "login" in task["prompt"].lower()
]

# Convert and run
results = await run_dataset(
    "Login Tasks Only",
    login_tasks,
    ClaudeAgent
)

Custom System Prompts

# Override dataset system prompt
results = await run_dataset(
    "Custom Evaluation",
    "hud-evals/SheetBench-50",
    ClaudeAgent,
    custom_system_prompt="You are an expert spreadsheet user. Be precise."
)

Environment Variable Management

# Tasks preserve templates
task = Task(
    prompt="Test",
    mcp_config={
        "server": {
            "api_key": "${API_KEY:default-key}"
        }
    }
)

# model_dump() preserves the template
data = task.model_dump()
assert data["mcp_config"]["server"]["api_key"] == "${API_KEY:default-key}"

# But task object has resolved value
os.environ["API_KEY"] = "real-key"
task2 = Task(**data)
# task2.mcp_config["server"]["api_key"] is now "real-key"

Get Started

Ideas

Environments

RL

Agents

CLI Reference

SDK Reference

Tasks

Task Class

Environment Variable Substitution

Field Validators

Recommended Evaluation Workflow

Step 1: Single Task Development

Step 2: Full Dataset Evaluation

Quick Reference

Dataset Functions

run_dataset

fetch_system_prompt_from_dataset

save_tasks

MCPToolCall Type

Real-World Examples

Loading Tasks from Datasets

Task Structure in Datasets

Creating and Saving Tasks

Agent Integration

Agent Config Options

Best Practices

Common Patterns

Filtering Tasks

Custom System Prompts

Environment Variable Management

See Also

Get Started

Ideas

Environments

RL

Agents

CLI Reference

SDK Reference

​Task Class

​Environment Variable Substitution

​Field Validators

​Recommended Evaluation Workflow

​Step 1: Single Task Development

​Step 2: Full Dataset Evaluation

​Quick Reference

​Dataset Functions

​run_dataset

​fetch_system_prompt_from_dataset

​save_tasks

​MCPToolCall Type

​Real-World Examples

​Loading Tasks from Datasets

​Task Structure in Datasets

​Creating and Saving Tasks

​Agent Integration

​Agent Config Options

​Best Practices

​Common Patterns

​Filtering Tasks

​Custom System Prompts

​Environment Variable Management

​See Also

Task Class

Environment Variable Substitution

Field Validators

Recommended Evaluation Workflow

Step 1: Single Task Development

Step 2: Full Dataset Evaluation

Quick Reference

Dataset Functions

run_dataset

fetch_system_prompt_from_dataset

save_tasks

MCPToolCall Type

Real-World Examples

Loading Tasks from Datasets

Task Structure in Datasets

Creating and Saving Tasks

Agent Integration

Agent Config Options

Best Practices

Common Patterns

Filtering Tasks

Custom System Prompts

Environment Variable Management

See Also