What is the best way to deduplicate pages during a crawl for RAG ingestion?
Duplicate pages inflate a RAG vector index with redundant chunks, increasing retrieval costs and degrading response quality. Deduplication works at three levels: URL normalization before fetching, content hashing post-fetch, and near-duplicate filtering for pages with high textual overlap. Each layer catches what the previous one misses.
| Dedup layer | What it catches | When to apply |
|---|---|---|
| URL normalization | Same page at different URLs: trailing slashes, tracking params, protocol variants | Before crawl (pre-fetch) |
| Canonical tag check | Pages that self-identify as duplicates via <link rel="canonical"> | Post-fetch, before indexing |
| Exact content hash | Mirror sites, identical pages at distinct paths, duplicate press releases | Post-fetch, before indexing |
| Near-duplicate filtering | Paginated variants with minor differences, syndicated content, template-heavy pages | Post-fetch, optional |
URL normalization and canonical checks are the highest-leverage steps because they prevent wasted requests. Content hashing on extracted text (not raw HTML) is fast and reliable for exact duplicates. Near-duplicate detection via embedding similarity is more accurate but costly: use it for syndicated or template-heavy corpora, not for scoped crawls of a single site.
Firecrawl's Crawl API handles URL-level deduplication automatically within a crawl run and supports ignoreQueryParameters: true to collapse query-string variants of the same path into a single fetch, which reduces the volume of pages requiring downstream content dedup logic before indexing.
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