MassGen Develops MassGen

This skill provides guidance for using MassGen to develop and improve itself. Choose the appropriate workflow based on what you're testing.

Two Workflows

• Automation Mode - Test backend functionality, coordination logic, agent responses

• Visual Evaluation - Test terminal display, colors, layout, UX

Workflow 1: Automation Mode

Use this to test functionality without visual inspection. Ideal for programmatic testing.

Running MassGen with Automation

Run MassGen in the background (exact mechanism depends on your tooling):

uv run massgen --automation --config massgen/configs/basic/multi/two_agents_gemini.yaml "What is 2+2?"

For MassGen agents: Use custom_tool__start_background_tool targeting mcp__command_line__execute_command , then poll with custom_tool__get_background_tool_status / custom_tool__get_background_tool_result . For Claude Code: Use Bash tool's run_in_background parameter.

Why Automation Mode

Feature Benefit

Clean output ~10 parseable lines vs 3,000+ ANSI codes

LOG_DIR printed First line shows log directory path

status.json Real-time monitoring file

Exit codes 0=success, 1=config, 2=execution, 3=timeout, 4=interrupted

Workspace isolation Safe parallel execution

Expected Output

LOG_DIR: .massgen/massgen_logs/log_20251120_143022_123456 STATUS: .massgen/massgen_logs/log_20251120_143022_123456/status.json

🤖 Multi-Agent Mode Agents: gemini-2.5-pro1, gemini-2.5-pro2 Question: What is 2+2?

============================================================ QUESTION: What is 2+2? [Coordination in progress - monitor status.json for real-time updates]

WINNER: gemini-2.5-pro1 DURATION: 33.4s ANSWER_PREVIEW: The answer is 4.

COMPLETED: 2 agents, 35.2s total

Parse LOG_DIR from the first line to find the log directory.

Monitoring Progress

Read the status.json file (updated every 2 seconds):

cat .massgen/massgen_logs/log_20251120_143022_123456/status.json

Key fields:

{ "coordination": { "completion_percentage": 65, "phase": "enforcement" }, "results": { "winner": null // null = running, "agent_id" = done }, "agents": { "agent_a": { "status": "streaming", "error": null } } }

Agent status values: waiting , streaming , answered , voted , completed , error

Reading Results

After completion (exit code 0):

Read final answer

cat [log_dir]/final/[winner]/answer.txt

Timing Expectations

• Standard tasks: 2-10 minutes

• Complex/meta tasks: 10-30 minutes

• Check if stuck: Read status.json - if completion_percentage increases, it's working

Advanced: Multiple Background Monitors

You can create multiple background monitoring tasks that run independently alongside the main MassGen process. Each monitor can track different aspects and write to separate log files for later inspection.

Approach

Create small Python scripts that run in background shells. Each script:

• Monitors a specific aspect (tokens, errors, progress, coordination, etc.)

• Writes timestamped data to its own log file

• Runs in a loop with sleep() intervals

• Can be checked anytime without blocking the main task

Example Monitor Scripts

Token Usage Monitor (token_monitor.py ):

import json, time, sys from pathlib import Path

log_dir = Path(sys.argv[1]) # Pass LOG_DIR as argument while True: if (log_dir / "status.json").exists(): with open(log_dir / "status.json") as f: data = json.load(f) with open("token_monitor.log", "a") as log: log.write(f"=== {time.strftime('%H:%M:%S')} ===\n") log.write(f"Tokens: {data.get('total_tokens_used', 0)}\n") log.write(f"Cost: ${data.get('total_cost', 0):.4f}\n\n") time.sleep(5)

Error Monitor (error_monitor.py ):

import time, sys from pathlib import Path

log_dir = Path(sys.argv[1]) while True: if log_dir.exists(): with open("error_monitor.log", "a") as log: log.write(f"=== {time.strftime('%H:%M:%S')} ===\n") errors = [] for logfile in log_dir.glob("*.log"): with open(logfile) as f: for line in f: if any(x in line.lower() for x in ['error', 'warning', 'failed']): errors.append(line.strip()) log.write('\n'.join(errors[-5:]) if errors else "No errors\n") log.write("\n") time.sleep(5)

Progress Monitor (progress_monitor.py ):

import json, time, sys from pathlib import Path

log_dir = Path(sys.argv[1]) while True: if (log_dir / "status.json").exists(): with open(log_dir / "status.json") as f: data = json.load(f) with open("progress_monitor.log", "a") as log: log.write(f"=== {time.strftime('%H:%M:%S')} ===\n") progress = data.get('completion_percentage', 0) active = sum(1 for a in data.get('agents', {}).values() if a.get('status') == 'active') log.write(f"Progress: {progress}% Active agents: {active}\n\n") time.sleep(5)

Coordination Monitor (coordination_monitor.py ):

import json, time, sys from pathlib import Path

log_dir = Path(sys.argv[1]) while True: if (log_dir / "status.json").exists(): with open(log_dir / "status.json") as f: data = json.load(f) coord = data.get('coordination', {}) with open("coordination_monitor.log", "a") as log: log.write(f"=== {time.strftime('%H:%M:%S')} ===\n") log.write(f"Phase: {coord.get('phase', 'unknown')}\n") log.write(f"Round: {coord.get('round', 0)}\n") log.write(f"Total answers: {coord.get('total_answers', 0)}\n\n") time.sleep(5)

Workflow

• Launch main task, parse the LOG_DIR from output

• Create monitor scripts as needed (write Python files)

• Launch monitors in background shells: python3 token_monitor.py [LOG_DIR] &

• Check monitor logs anytime by reading the .log files

• When complete, kill monitor processes and analyze logs

Custom Monitors

Create monitors for any metric you want to track:

• Model-specific performance metrics

• Memory/context usage patterns

• Real-time cost accumulation

• Answer quality trends

• Agent coordination patterns

• Specific error categories

Benefits:

• Non-blocking inspection of specific metrics on demand

• Historical data captured for post-run analysis

• Independent monitoring streams for different aspects

• Easy to add new monitors without modifying configs

Workflow 2: Visual Evaluation

Use this to analyze and improve MassGen's terminal display quality. Requires tools from custom_tools/_multimodal_tools/ .

Important: This workflow records the rich terminal display, so the actual recording does NOT use --automation mode. However, you should ALWAYS pre-test with --automation first.

Prerequisites

You should have these tools available in your workspace:

• run_massgen_with_recording

• Records terminal sessions as video

• understand_video

• Analyzes video frames with GPT-4.1 vision

Step 0: Pre-Test with Automation (REQUIRED)

Before recording the video, verify the config works and API keys are valid:

Start with --automation to verify everything works

uv run massgen --automation --config [config_path] "[question]"

Wait 30-60 seconds (enough to verify API keys, config parsing, tool initialization), then kill the process.

Why this is critical:

• Detects config errors before wasting recording time

• Validates API keys are present and working

• Ensures tools initialize correctly

• Prevents recording a broken session

If the automation test fails, fix the issues before proceeding to recording.

Step 1: Record a MassGen Session

After the automation pre-test succeeds, record the visual session:

from custom_tools._multimodal_tools.run_massgen_with_recording import run_massgen_with_recording

result = await run_massgen_with_recording( config_path="massgen/configs/basic/multi/two_agents_gemini.yaml", question="What is 2+2?", output_format="mp4", # ALWAYS use mp4 for maximum compatibility timeout_seconds=120, width=1920, height=1080 )

Format recommendation: Always use "mp4" for maximum compatibility. GIF and WebM are supported but MP4 is preferred.

The recording captures: Rich terminal display with colors, status indicators, coordination visualization (WITHOUT --automation flag).

Step 2: Analyze the Recording

Use understand_video to analyze the MP4 recording. Call it at least once, but as many as multiple times to analyze different aspects:

from custom_tools._multimodal_tools.understand_video import understand_video

Overall UX evaluation

ux_eval = await understand_video( video_path=result["video_path"], # The MP4 file from Step 1 prompt="Evaluate the overall terminal display quality, clarity, and usability", num_frames=12 )

Focused on coordination

coordination_eval = await understand_video( video_path=result["video_path"], prompt="How clearly does the display show agent coordination phases and voting?", num_frames=8 )

Status indicators

status_eval = await understand_video( video_path=result["video_path"], prompt="Are status indicators (streaming, answered, voted) clear and visually distinct?", num_frames=8 )

Key points:

• The recording tool saves the video to workspace - use that path for analysis

• You can call understand_video multiple times on the same video with different prompts

• Each call focuses on a specific aspect (UX, coordination, status, colors, etc.)

Evaluation Criteria

When analyzing terminal displays, assess:

• Visual Clarity - Contrast, colors, font rendering, ANSI handling, spacing

• Information Organization - Layout, content density, streaming display, scroll handling

• Status Indicators - Agent states, progress tracking, phase transitions, winner selection

• User Experience - Real-time feedback, error visibility, cognitive load, information hierarchy

Output Format Recommendations

Default to MP4 - Maximum compatibility and quality.

Format Use Case Notes

MP4 Default - use for everything Best quality, universally supported, ideal for detailed analysis

GIF Smaller file size, easy embedding Lower quality, larger files than expected, avoid unless size-constrained

WebM Modern web publishing Good quality, not universally supported

Rule of thumb: Use MP4 unless you have a specific reason not to.

Frame Count Guidelines

Frames Use Case

4-8 Quick evaluation

8-12 Standard evaluation

12-16+ Detailed analysis

Which Configs to Test

Model Selection Guidelines

Default to mid-tier models when generating configs or running experiments. These provide the best balance of cost, speed, and capability for development and testing.

CRITICAL: Always check model recency based on TODAY'S DATE. Models older than 6-12 months should be considered outdated.

How to Select Models

Step 1: Read backend files to check release dates

Check Gemini models and their release dates

grep -A 5 "model.*2." massgen/backend/gemini.py

Check OpenAI models and their release dates

grep -A 5 "model.*gpt" massgen/backend/openai.py

Check Claude models and their release dates

grep -A 5 "model.*claude" massgen/backend/claude.py

Step 2: Check token costs

cat docs/source/reference/token_budget.rst | grep -A 3 "gemini|gpt|claude"

Step 3: Compare release dates against today's date

• Calculate months since release: (today's year-month) - (model release year-month)

• If > 12 months: Model is outdated

• If 6-12 months: Model is aging, prefer newer if available

• If < 6 months: Model is current

Model Selection Examples

✅ GOOD (Recent, mid-tier patterns):

• Gemini: gemini-2.5-pro , gemini-2.5-flash (2.x series, 2025)

• OpenAI: gpt-5-mini , gpt-4o-mini (GPT-5 generation)

• Claude: claude-sonnet-4-* (4.x series, 2025)

⚠️ BAD (Outdated patterns - check dates!):

• ❌ gpt-4o (2024 release - likely >12 months old)

• ❌ gpt-4-turbo (2023-2024 era)

• ❌ gemini-1.5-pro (1.x series deprecated by 2.x)

• ❌ claude-3.5-sonnet (3.x series when 4.x exists)

Selection criteria:

• Recency: Released within last 6-12 months (ALWAYS check backend files for dates)

• Mid-range pricing: Not top-tier (expensive) or bottom-tier (cheap)

• General availability: Stable release, not experimental/preview/alpha

• Version numbers: Higher major versions are newer (gemini-2.x > gemini-1.x, gpt-5 > gpt-4, claude-4 > claude-3)

When to deviate:

• Premium models: Testing model ceiling capabilities (e.g., gpt-5 , claude-opus-4 , gemini-3-pro )

• Budget models: Cost optimization experiments (e.g., gpt-5-mini , gemini-2.5-flash )

• Legacy testing: Validating backwards compatibility with older models

Generating a Config (Agent-Friendly)

Use --generate-config for programmatic config generation:

WORKFLOW:

1. Read backend file to find recent mid-tier models

2. Verify release date (< 12 months old)

3. Check pricing tier (mid-range)

4. Use model in --config-model flag

Example: Generate 2-agent config

massgen --generate-config ./test_config.yaml
--config-backend gemini
--config-model gemini-2.5-pro \ # (example - always verify this is current!) --config-agents 2
--config-docker

With context path

massgen --generate-config ./test_config.yaml
--config-backend openai
--config-model gpt-5-mini \ # (example - always verify this is current!) --config-context-path /path/to/project

IMPORTANT: The model names shown above are EXAMPLES. Always check backend files for current models based on today's date.

This creates a full-featured config with code-based tools, skills, and task planning enabled.

Testing Specific Features

Modify the generated config to enable/disable features:

Code execution:

agents:

• backend: enable_mcp_command_line: true command_line_execution_mode: "docker"

Custom tools:

agents:

• backend: enable_code_based_tools: true auto_discover_custom_tools: true

Different models per agent:

agents:

• backend: {type: "gemini", model: "gemini-2.5-pro"}
• backend: {type: "openai", model: "gpt-5-mini"}

Common parameters: enable_code_based_tools , enable_mcp_command_line , command_line_execution_mode , auto_discover_custom_tools , timeout_settings

Docker Considerations

Automatic Docker Detection

MassGen automatically detects when running inside a Docker container. If a config has command_line_execution_mode: "docker" , MassGen will:

• Detect the container environment (via /.dockerenv )

• Automatically switch to "local" execution mode

• Log: "Already running inside Docker container - switching to local execution mode"

Why this works: The outer container already provides isolation. Running "locally" within that container is safe and sandboxed.

No manual configuration needed - configs with Docker mode just work when run inside containers.

Tradeoffs

When auto-switching to local execution:

• ✅ Still sandboxed from host

• ✅ All features work (VHS, MassGen, tools are in container)

• ⚠️ No per-execution isolation between tool calls

• ⚠️ State persists within container session

Reference Files

• Status file docs: docs/source/reference/status_file.rst

• Terminal evaluation docs: docs/source/user_guide/terminal_evaluation.rst

• Example configs: massgen/configs/basic/ , massgen/configs/meta/

• Recording tool: massgen/tool/_multimodal_tools/run_massgen_with_recording.py

• Video analysis tool: massgen/tool/_multimodal_tools/understand_video.py