What are Community Notes?

Community Notes (formerly known as Birdwatch) is X’s crowd-sourced fact-checking system that allows contributors to add helpful context to potentially misleading posts. The system uses a novel bridging-based ranking algorithm to identify notes that people from different perspectives find helpful.

How does it work?

At a high level, Community Notes works in three main steps:

1. Note Writing: Contributors write notes providing context on posts they believe could be misleading
2. Note Rating: Other contributors rate these notes on helpfulness
3. Algorithmic Ranking: An algorithm identifies which notes are helpful to people across different viewpoints

The Bridging-Based Algorithm

The core innovation in Community Notes is its bridging-based ranking algorithm. Here’s how it works:

1. Creating the Rating Network

First, the system creates a network based on how contributors rate notes:

• Each contributor is a node in the network
• Edges are created between contributors who tend to agree in their note ratings
• The strength of edges depends on rating similarity

2. Identifying Perspectives

The algorithm then:

• Uses network clustering to identify groups of contributors with similar rating patterns
• These groups often correspond to different perspectives or viewpoints on issues
• The goal is to find notes that bridge across these different groups

3. Scoring Notes

A note’s final status depends on:

• Getting high helpfulness ratings overall
• Crucially, getting high ratings from contributors across different clusters
• Meeting certain rating thresholds within a time window

# Simplified pseudocode for note scoring
def score_note(note, ratings, contributor_clusters):
    scores_by_cluster = {}
    
    for cluster in contributor_clusters:
        cluster_ratings = [r for r in ratings if r.rater in cluster]
        scores_by_cluster[cluster] = mean(cluster_ratings)
    
    # Note needs high scores across clusters
    bridging_score = min(scores_by_cluster.values())
    return bridging_score

Why is this approach effective?

The bridging-based approach has several key advantages:

1. Reduces Polarization: By requiring agreement across perspectives, it helps surface notes that are broadly credible rather than just popular within one group

2. Resists Gaming: Makes it harder for coordinated groups to manipulate the system since they need broad consensus

3. Promotes Better Notes: Incentivizes contributors to write notes that are factual and neutrally worded to appeal across perspectives

Current Challenges & Future Work

While Community Notes has shown promise, some open challenges include:

• Scaling to more languages and regions
• Handling rapidly evolving situations
• Balancing speed vs accuracy
• Preventing harassment of contributors

Learn More

For a deeper technical dive, check out:

• The Community Notes Guide
• Our recent paper on Supernotes
• X’s official documentation

Last updated: March 14, 2024