| name | x-algo-filters |
| description | Explain why posts get filtered from the X feed. Use when analyzing why a post was removed, not shown, or filtered out of recommendations. |
X Algorithm Filters
The X algorithm applies 12 filters to remove posts that shouldn't appear in a user's feed. Filters run at multiple stages of the pipeline.
Filter Summary
| Filter | Purpose | Source File |
|---|
AgeFilter | Remove posts older than max age | age_filter.rs |
PreviouslySeenPostsFilter | Remove posts user has seen | previously_seen_posts_filter.rs |
PreviouslyServedPostsFilter | Remove posts already served in session | previously_served_posts_filter.rs |
DropDuplicatesFilter | Remove duplicate tweet IDs | drop_duplicates_filter.rs |
RetweetDeduplicationFilter | Remove duplicate retweets | retweet_deduplication_filter.rs |
DedupConversationFilter | Keep only best post per conversation | dedup_conversation_filter.rs |
SelfTweetFilter | Remove user's own posts | self_tweet_filter.rs |
AuthorSocialgraphFilter | Remove blocked/muted authors | author_socialgraph_filter.rs |
MutedKeywordFilter | Remove posts with muted keywords | muted_keyword_filter.rs |
VFFilter | Safety/visibility filtering | vf_filter.rs |
CoreDataHydrationFilter | Remove posts missing required data | core_data_hydration_filter.rs |
IneligibleSubscriptionFilter | Remove subscription posts user can't see | ineligible_subscription_filter.rs |
Filter Details
1. AgeFilter
Removes posts older than a configured maximum age using Snowflake ID timestamp extraction.
pub struct AgeFilter {
pub max_age: Duration,
}
fn is_within_age(&self, tweet_id: i64) -> bool {
snowflake::duration_since_creation_opt(tweet_id)
.map(|age| age <= self.max_age)
.unwrap_or(false)
}
Why filtered: Post is too old. Snowflake IDs encode creation timestamp.
2. PreviouslySeenPostsFilter
Uses Bloom filters and explicit seen IDs from the client to filter posts the user has already viewed.
let (removed, kept) = candidates.into_iter().partition(|c| {
get_related_post_ids(c).iter().any(|&post_id| {
query.seen_ids.contains(&post_id)
|| bloom_filters
.iter()
.any(|filter| filter.may_contain(post_id))
})
});
Why filtered: User has already seen this post (tracked via Bloom filter or explicit ID list).
3. PreviouslyServedPostsFilter
Removes posts already served in the current session (for "load more" / infinite scroll).
fn enable(&self, query: &ScoredPostsQuery) -> bool {
query.is_bottom_request
}
get_related_post_ids(c).iter().any(|id| query.served_ids.contains(id))
Why filtered: Post was already served earlier in this session.
4. DropDuplicatesFilter
Simple deduplication by tweet ID within the candidate set.
let mut seen_ids = HashSet::new();
for candidate in candidates {
if seen_ids.insert(candidate.tweet_id) {
kept.push(candidate);
} else {
removed.push(candidate);
}
}
Why filtered: Duplicate tweet ID from multiple sources.
5. RetweetDeduplicationFilter
Prevents showing the same underlying post multiple times (as original or as different retweets).
match candidate.retweeted_tweet_id {
Some(retweeted_id) => {
if seen_tweet_ids.insert(retweeted_id) {
kept.push(candidate);
} else {
removed.push(candidate);
}
}
None => {
seen_tweet_ids.insert(candidate.tweet_id as u64);
kept.push(candidate);
}
}
Why filtered: Another version of this post (original or retweet) already included.
6. DedupConversationFilter
Keeps only the highest-scored post per conversation thread.
fn get_conversation_id(candidate: &PostCandidate) -> u64 {
candidate
.ancestors
.iter()
.copied()
.min()
.unwrap_or(candidate.tweet_id as u64)
}
Why filtered: Another post in same conversation thread has higher score.
7. SelfTweetFilter
Removes the user's own posts from their "For You" feed.
let viewer_id = query.user_id as u64;
let (kept, removed) = candidates
.into_iter()
.partition(|c| c.author_id != viewer_id);
Why filtered: Post authored by the viewing user.
8. AuthorSocialgraphFilter
Removes posts from authors the user has blocked or muted.
let muted = viewer_muted_user_ids.contains(&author_id);
let blocked = viewer_blocked_user_ids.contains(&author_id);
if muted || blocked {
removed.push(candidate);
}
Why filtered: Author is in user's blocked or muted list.
9. MutedKeywordFilter
Removes posts containing keywords the user has muted.
let tweet_text_token_sequence = self.tokenizer.tokenize(&candidate.tweet_text);
if matcher.matches(&tweet_text_token_sequence) {
removed.push(candidate);
}
Why filtered: Post text contains muted keyword(s).
10. VFFilter (Visibility Filtering)
Safety-based filtering using the visibility filtering service.
fn should_drop(reason: &Option<FilteredReason>) -> bool {
match reason {
Some(FilteredReason::SafetyResult(safety_result)) => {
matches!(safety_result.action, Action::Drop(_))
}
Some(_) => true,
None => false,
}
}
Why filtered: Safety violation detected (spam, abuse, policy violation, etc.).
11. CoreDataHydrationFilter
Removes posts that failed to hydrate required data.
let (kept, removed) = candidates
.into_iter()
.partition(|c| c.author_id != 0 && !c.tweet_text.trim().is_empty());
Why filtered: Missing author ID or empty tweet text (hydration failed).
12. IneligibleSubscriptionFilter
Removes subscription-only posts from authors the user isn't subscribed to.
let (kept, removed) = candidates.into_iter().partition(|candidate| {
match candidate.subscription_author_id {
Some(author_id) => subscribed_user_ids.contains(&author_id),
None => true,
}
});
Why filtered: Post requires subscription to author, user not subscribed.
Filter Result Structure
All filters return:
pub struct FilterResult<T> {
pub kept: Vec<T>,
pub removed: Vec<T>,
}
Conditional Filter Enabling
Some filters only run in certain contexts:
fn enable(&self, query: &ScoredPostsQuery) -> bool {
query.is_bottom_request
}
Bloom Filter Deduplication
PreviouslySeenPostsFilter uses Bloom filters for efficient "seen" tracking:
- Client sends Bloom filter entries with request
- Server reconstructs filters via
BloomFilter::from_entry
- Uses
may_contain() (probabilistic) for fast lookup
- Falls back to explicit
seen_ids for definitive checks
Related Skills
/x-algo-pipeline - Where filters fit in the full pipeline/x-algo-engagement - Understanding what data filters check against
