---
name: evaluating-llms-harness
description: Evaluates LLMs across 60+ academic benchmarks (MMLU, HumanEval, GSM8K, TruthfulQA, HellaSwag) using standardized prompts and metrics. Supports HuggingFace, vLLM, and API backends.
license: MIT
---

# lm-evaluation-harness - LLM Benchmarking

## Quick start

lm-evaluation-harness evaluates LLMs across 60+ academic benchmarks using standardized prompts and metrics.

**Installation**:
```bash
pip install lm-eval
```

**Evaluate any HuggingFace model**:
```bash
lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf \
  --tasks mmlu,gsm8k,hellaswag \
  --device cuda:0 \
  --batch_size 8
```

**View available tasks**:
```bash
lm_eval --tasks list
```

## Common workflows

### Workflow 1: Standard benchmark evaluation

Evaluate model on core benchmarks (MMLU, GSM8K, HumanEval).

Copy this checklist:

```
Benchmark Evaluation:
- [ ] Step 1: Choose benchmark suite
- [ ] Step 2: Configure model
- [ ] Step 3: Run evaluation
- [ ] Step 4: Analyze results
```

**Step 1: Choose benchmark suite**

**Core reasoning benchmarks**:
- **MMLU** (Massive Multitask Language Understanding) - 57 subjects, multiple choice
- **GSM8K** - Grade school math word problems
- **HellaSwag** - Common sense reasoning
- **TruthfulQA** - Truthfulness and factuality
- **ARC** (AI2 Reasoning Challenge) - Science questions

**Code benchmarks**:
- **HumanEval** - Python code generation (164 problems)
- **MBPP** (Mostly Basic Python Problems) - Python coding

**Standard suite** (recommended for model releases):
```bash
--tasks mmlu,gsm8k,hellaswag,truthfulqa,arc_challenge
```

**Step 2: Configure model**

**HuggingFace model**:
```bash
lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf,dtype=bfloat16 \
  --tasks mmlu \
  --device cuda:0 \
  --batch_size auto  # Auto-detect optimal batch size
```

**Quantized model (4-bit/8-bit)**:
```bash
lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf,load_in_4bit=True \
  --tasks mmlu \
  --device cuda:0
```

**Custom checkpoint**:
```bash
lm_eval --model hf \
  --model_args pretrained=/path/to/my-model,tokenizer=/path/to/tokenizer \
  --tasks mmlu \
  --device cuda:0
```

**Step 3: Run evaluation**

```bash
# Full MMLU evaluation (57 subjects)
lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf \
  --tasks mmlu \
  --num_fewshot 5 \  # 5-shot evaluation (standard)
  --batch_size 8 \
  --output_path results/ \
  --log_samples  # Save individual predictions

# Multiple benchmarks at once
lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf \
  --tasks mmlu,gsm8k,hellaswag,truthfulqa,arc_challenge \
  --num_fewshot 5 \
  --batch_size 8 \
  --output_path results/llama2-7b-eval.json
```

**Step 4: Analyze results**

Results saved to `results/llama2-7b-eval.json`:

```json
{
  "results": {
    "mmlu": {
      "acc": 0.459,
      "acc_stderr": 0.004
    },
    "gsm8k": {
      "exact_match": 0.142,
      "exact_match_stderr": 0.006
    },
    "hellaswag": {
      "acc_norm": 0.765,
      "acc_norm_stderr": 0.004
    }
  },
  "config": {
    "model": "hf",
    "model_args": "pretrained=meta-llama/Llama-2-7b-hf",
    "num_fewshot": 5
  }
}
```

### Workflow 2: Track training progress

Evaluate checkpoints during training.

```
Training Progress Tracking:
- [ ] Step 1: Set up periodic evaluation
- [ ] Step 2: Choose quick benchmarks
- [ ] Step 3: Automate evaluation
- [ ] Step 4: Plot learning curves
```

**Step 1: Set up periodic evaluation**

Evaluate every N training steps:

```bash
#!/bin/bash
# eval_checkpoint.sh

CHECKPOINT_DIR=$1
STEP=$2

lm_eval --model hf \
  --model_args pretrained=$CHECKPOINT_DIR/checkpoint-$STEP \
  --tasks gsm8k,hellaswag \
  --num_fewshot 0 \  # 0-shot for speed
  --batch_size 16 \
  --output_path results/step-$STEP.json
```

**Step 2: Choose quick benchmarks**

Fast benchmarks for frequent evaluation:
- **HellaSwag**: ~10 minutes on 1 GPU
- **GSM8K**: ~5 minutes
- **PIQA**: ~2 minutes

Avoid for frequent eval (too slow):
- **MMLU**: ~2 hours (57 subjects)
- **HumanEval**: Requires code execution

**Step 3: Automate evaluation**

Integrate with training script:

```python
# In training loop
if step % eval_interval == 0:
    model.save_pretrained(f"checkpoints/step-{step}")

    # Run evaluation
    os.system(f"./eval_checkpoint.sh checkpoints step-{step}")
```

Or use PyTorch Lightning callbacks:

```python
from pytorch_lightning import Callback

class EvalHarnessCallback(Callback):
    def on_validation_epoch_end(self, trainer, pl_module):
        step = trainer.global_step
        checkpoint_path = f"checkpoints/step-{step}"

        # Save checkpoint
        trainer.save_checkpoint(checkpoint_path)

        # Run lm-eval
        os.system(f"lm_eval --model hf --model_args pretrained={checkpoint_path} ...")
```

**Step 4: Plot learning curves**

```python
import json
import matplotlib.pyplot as plt

# Load all results
steps = []
mmlu_scores = []

for file in sorted(glob.glob("results/step-*.json")):
    with open(file) as f:
        data = json.load(f)
        step = int(file.split("-")[1].split(".")[0])
        steps.append(step)
        mmlu_scores.append(data["results"]["mmlu"]["acc"])

# Plot
plt.plot(steps, mmlu_scores)
plt.xlabel("Training Step")
plt.ylabel("MMLU Accuracy")
plt.title("Training Progress")
plt.savefig("training_curve.png")
```

### Workflow 3: Compare multiple models

Benchmark suite for model comparison.

```
Model Comparison:
- [ ] Step 1: Define model list
- [ ] Step 2: Run evaluations
- [ ] Step 3: Generate comparison table
```

**Step 1: Define model list**

```bash
# models.txt
meta-llama/Llama-2-7b-hf
meta-llama/Llama-2-13b-hf
mistralai/Mistral-7B-v0.1
microsoft/phi-2
```

**Step 2: Run evaluations**

```bash
#!/bin/bash
# eval_all_models.sh

TASKS="mmlu,gsm8k,hellaswag,truthfulqa"

while read model; do
    echo "Evaluating $model"

    # Extract model name for output file
    model_name=$(echo $model | sed 's/\//-/g')

    lm_eval --model hf \
      --model_args pretrained=$model,dtype=bfloat16 \
      --tasks $TASKS \
      --num_fewshot 5 \
      --batch_size auto \
      --output_path results/$model_name.json

done < models.txt
```

**Step 3: Generate comparison table**

```python
import json
import pandas as pd

models = [
    "meta-llama-Llama-2-7b-hf",
    "meta-llama-Llama-2-13b-hf",
    "mistralai-Mistral-7B-v0.1",
    "microsoft-phi-2"
]

tasks = ["mmlu", "gsm8k", "hellaswag", "truthfulqa"]

results = []
for model in models:
    with open(f"results/{model}.json") as f:
        data = json.load(f)
        row = {"Model": model.replace("-", "/")}
        for task in tasks:
            # Get primary metric for each task
            metrics = data["results"][task]
            if "acc" in metrics:
                row[task.upper()] = f"{metrics['acc']:.3f}"
            elif "exact_match" in metrics:
                row[task.upper()] = f"{metrics['exact_match']:.3f}"
        results.append(row)

df = pd.DataFrame(results)
print(df.to_markdown(index=False))
```

Output:
```
| Model                  | MMLU  | GSM8K | HELLASWAG | TRUTHFULQA |
|------------------------|-------|-------|-----------|------------|
| meta-llama/Llama-2-7b  | 0.459 | 0.142 | 0.765     | 0.391      |
| meta-llama/Llama-2-13b | 0.549 | 0.287 | 0.801     | 0.430      |
| mistralai/Mistral-7B   | 0.626 | 0.395 | 0.812     | 0.428      |
| microsoft/phi-2        | 0.560 | 0.613 | 0.682     | 0.447      |
```

### Workflow 4: Evaluate with vLLM (faster inference)

Use vLLM backend for 5-10x faster evaluation.

```
vLLM Evaluation:
- [ ] Step 1: Install vLLM
- [ ] Step 2: Configure vLLM backend
- [ ] Step 3: Run evaluation
```

**Step 1: Install vLLM**

```bash
pip install vllm
```

**Step 2: Configure vLLM backend**

```bash
lm_eval --model vllm \
  --model_args pretrained=meta-llama/Llama-2-7b-hf,tensor_parallel_size=1,dtype=auto,gpu_memory_utilization=0.8 \
  --tasks mmlu \
  --batch_size auto
```

**Step 3: Run evaluation**

vLLM is 5-10× faster than standard HuggingFace:

```bash
# Standard HF: ~2 hours for MMLU on 7B model
lm_eval --model hf \
  --model_args pretrained=meta-llama/Llama-2-7b-hf \
  --tasks mmlu \
  --batch_size 8

# vLLM: ~15-20 minutes for MMLU on 7B model
lm_eval --model vllm \
  --model_args pretrained=meta-llama/Llama-2-7b-hf,tensor_parallel_size=2 \
  --tasks mmlu \
  --batch_size auto
```

## When to use vs alternatives

**Use lm-evaluation-harness when:**
- Benchmarking models for academic papers
- Comparing model quality across standard tasks
- Tracking training progress
- Reporting standardized metrics (everyone uses same prompts)
- Need reproducible evaluation

**Use alternatives instead:**
- **HELM** (Stanford): Broader evaluation (fairness, efficiency, calibration)
- **AlpacaEval**: Instruction-following evaluation with LLM judges
- **MT-Bench**: Conversational multi-turn evaluation
- **Custom scripts**: Domain-specific evaluation

## Common issues

**Issue: Evaluation too slow**

Use vLLM backend:
```bash
lm_eval --model vllm \
  --model_args pretrained=model-name,tensor_parallel_size=2
```

Or reduce fewshot examples:
```bash
--num_fewshot 0  # Instead of 5
```

Or evaluate subset of MMLU:
```bash
--tasks mmlu_stem  # Only STEM subjects
```

**Issue: Out of memory**

Reduce batch size:
```bash
--batch_size 1  # Or --batch_size auto
```

Use quantization:
```bash
--model_args pretrained=model-name,load_in_8bit=True
```

Enable CPU offloading:
```bash
--model_args pretrained=model-name,device_map=auto,offload_folder=offload
```

**Issue: Different results than reported**

Check fewshot count:
```bash
--num_fewshot 5  # Most papers use 5-shot
```

Check exact task name:
```bash
--tasks mmlu  # Not mmlu_direct or mmlu_fewshot
```

Verify model and tokenizer match:
```bash
--model_args pretrained=model-name,tokenizer=same-model-name
```

**Issue: HumanEval not executing code**

Install execution dependencies:
```bash
pip install human-eval
```

Enable code execution:
```bash
lm_eval --model hf \
  --model_args pretrained=model-name \
  --tasks humaneval \
  --allow_code_execution  # Required for HumanEval
```

## Advanced topics

**Benchmark descriptions**: See [references/benchmark-guide.md](references/benchmark-guide.md) for detailed description of all 60+ tasks, what they measure, and interpretation.

**Custom tasks**: See [references/custom-tasks.md](references/custom-tasks.md) for creating domain-specific evaluation tasks.

**API evaluation**: See [references/api-evaluation.md](references/api-evaluation.md) for evaluating OpenAI, Anthropic, and other API models.

**Multi-GPU strategies**: See [references/distributed-eval.md](references/distributed-eval.md) for data parallel and tensor parallel evaluation.

## Hardware requirements

- **GPU**: NVIDIA (CUDA 11.8+), works on CPU (very slow)
- **VRAM**:
  - 7B model: 16GB (bf16) or 8GB (8-bit)
  - 13B model: 28GB (bf16) or 14GB (8-bit)
  - 70B model: Requires multi-GPU or quantization
- **Time** (7B model, single A100):
  - HellaSwag: 10 minutes
  - GSM8K: 5 minutes
  - MMLU (full): 2 hours
  - HumanEval: 20 minutes

## Resources

- GitHub: https://github.com/EleutherAI/lm-evaluation-harness
- Docs: https://github.com/EleutherAI/lm-evaluation-harness/tree/main/docs
- Task library: 60+ tasks including MMLU, GSM8K, HumanEval, TruthfulQA, HellaSwag, ARC, WinoGrande, etc.
- Leaderboard: https://huggingface.co/spaces/HuggingFaceH4/open_llm_leaderboard (uses this harness)