ESMFold vs AlphaFold2 vs Boltz-2: Which Protein Folding Tool Should You Use?

Why Comparing Protein Folding Tools Matters

The protein structure prediction landscape has evolved rapidly since AlphaFold2's breakthrough in 2020. Researchers and developers now have multiple tools to choose from, each with different strengths. Picking the wrong tool can mean wasted GPU hours, unnecessary latency, or missing important structural features like multi-chain interactions.

This guide provides a practical comparison of the three most relevant protein folding tools available today: ESMFold, AlphaFold2, and Boltz-2. We focus on the factors that matter for real-world use: speed, accuracy, input requirements, and API availability.

Head-to-Head Comparison

Speed

• ESMFold: 5 to 15 seconds per prediction. No MSA required, so the entire pipeline is fast.
• AlphaFold2: 5 minutes to 2 hours. MSA construction dominates the runtime, especially for novel sequences.
• Boltz-2: 30 seconds to 5 minutes. Faster than AlphaFold2 but slower than ESMFold due to complex architecture.

Accuracy

• AlphaFold2: Gold standard for single-chain accuracy. Median GDT-TS above 90 on CASP14 targets.
• ESMFold: Comparable to AlphaFold2 on proteins with many homologs. Slightly lower accuracy on orphan proteins with limited evolutionary information.
• Boltz-2: Competitive single-chain accuracy. Superior on multi-chain complexes where it models inter-chain contacts directly.

Input Requirements

• ESMFold: Single amino acid sequence. No databases, no MSA, no templates.
• AlphaFold2: Amino acid sequence plus MSA from sequence databases (UniRef90, MGnify, BFD). Requires several TB of database storage.
• Boltz-2: Amino acid sequences for all chains. Optionally accepts ligand structures in SMILES or SDF format.

Complex and Multimer Support

• ESMFold: Single chain only. Cannot predict protein-protein or protein-ligand complexes.
• AlphaFold2 (Multimer): Supports homo- and heteromeric complexes, but requires MSAs for each chain.
• Boltz-2: Full complex support including protein-protein, protein-ligand, and protein-nucleic acid interactions.

API Availability and Cost

• ESMFold via SciRouter: Hosted API, pay-per-prediction, 500 free credits/month. No infrastructure to manage.
• AlphaFold2: Self-hosted only. Requires GPU instance and terabytes of sequence databases. No widely available hosted API.
• Boltz-2 via SciRouter: Hosted API, pay-per-prediction. Higher cost per prediction than ESMFold due to GPU requirements.

When to Use Each Tool

Choose ESMFold When:

• You need results in seconds, not minutes
• You are screening hundreds or thousands of sequences
• You want a simple API call without managing infrastructure
• You are working with single-chain proteins
• You need to identify disordered regions via pLDDT scores

Choose AlphaFold2 When:

• Maximum single-chain accuracy is critical (e.g., drug target characterization)
• You have the infrastructure to run MSA searches
• You are working with a small number of high-priority targets
• The target has few sequence homologs and needs evolutionary signal from deep MSAs

Choose Boltz-2 When:

• You need to predict multi-chain complexes
• You are studying protein-ligand or protein-nucleic acid interactions
• You want complex prediction without managing AlphaFold-Multimer infrastructure
• You need an API-accessible alternative to AlphaFold3

A Combined Workflow

In practice, many teams use these tools in combination. A typical pipeline might look like this:

import requests

API_KEY = "sk-sci-your-api-key"
BASE = "https://api.scirouter.ai/v1"
headers = {"Authorization": f"Bearer {API_KEY}"}

sequences = ["MVLSPADK...", "MNIFEML...", "GKIFVQR..."]

# Step 1: Quick screen with ESMFold
for seq in sequences:
    job = requests.post(f"{BASE}/proteins/fold", headers=headers,
                        json={"sequence": seq, "model": "esmfold"}).json()
    # ... poll and check mean_plddt

# Step 2: For top hits, predict complexes with Boltz-2
job = requests.post(f"{BASE}/proteins/fold", headers=headers,
                    json={
                        "sequences": [best_hit, partner_chain],
                        "model": "boltz2"
                    }).json()
# ... poll for complex structure

Try Them on SciRouter

Both ESMFold and Boltz-2 are available through SciRouter with a unified API and free credits to get started. Read our ESMFold guide or step-by-step tutorial to start predicting structures today.

Sign up for a free API key and run your first prediction in under a minute. No GPU setup, no database downloads, no infrastructure to maintain.