When multiple job boards describe one vacancy differently, a job title is not a dependable deduplication key. Start with the apply URL: normalize redirects and tracking parameters, then extract a requisition identifier when it belongs to a known ATS posting pattern. Keep each board’s original record and evidence so you can group likely copies without losing traceability.
Why the same vacancy appears as several API results
Aggregators and employer career pages can expose separate records for one opening. Their titles may differ because one board abbreviates a role, another rewrites it, and the employer uses its own wording. In the example described by a DEV Community search-result extract published October 6, 2026, a search for “python developer” plus remote returned 30 results, including four versions of one Berlin fintech requisition across three aggregators and the employer board. Exact-title matching and company-plus-lowercased-title checks did not catch every copy; the apply URL exposed a canonical requisition ID. This is an author-reported example, not a general estimate of how often duplicates occur. Read the example.
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The broader problem is consistent with a 2024 preprint on job-posting duplicate detection: postings for the same job can have varying text. A title-only key can therefore miss copies, while a loose content match can accidentally combine distinct openings. See the preprint.
How to use an apply URL as identity evidence
An apply URL may contain an ATS or employer requisition identifier that remains the same when a listing is mirrored elsewhere. Treat it as evidence to parse, not as a universal key: URL formats vary, and some links lead only to a general application route.
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- Save the original result. Retain the provider’s job ID, source or board, employer, title, location, posting URL, apply URL, and retrieval time. Keep the raw apply URL even after normalizing it.
- Normalize cautiously. Follow redirects, or interpret them where following is not permitted. Remove known tracking parameters and normalize host and path. Do not remove parameters that carry the requisition ID.
- Parse recognized ATS patterns. Extract an ID only from a URL format you know, and validate that it identifies a posting rather than a generic application page. Keep the parser provider-specific and versioned so you can revise it without losing the original evidence.
- Compare the resulting evidence. Prefer an explicit shared requisition ID. If the identifier is meaningful only within an employer or ATS, combine it with that employer or ATS host. If there is no stable ID, use the URL alongside employer, title, location, and description evidence.
- Store a reversible grouping. Record which source listings were associated and why. Avoid destructively deleting or overwriting records; users should be able to inspect the cluster and separate listings when the evidence changes.
Normalization must not erase identity. Stripping every query parameter, for example, may discard the very requisition value that makes two links comparable. Preserve both the untouched URL and the normalized form, and document which transformations your parser applied.
Choose a deduplication method that matches the evidence
| Method | Identity strength | Main risk or limit | Best use |
|---|---|---|---|
| Shared ATS or employer requisition ID | Strong when the ID is parsed from a recognized posting URL and scoped to the correct employer or ATS | A parser can mistake a generic route or unrelated parameter for a job ID; IDs may not be globally unique | Primary grouping signal when the identifier is validated |
| Normalized apply URL plus employer evidence | Useful when the same posting link is reused across sources | Redirects and tracking parameters can make links differ; overly aggressive normalization can remove meaningful values | Compare links after preserving raw URLs and applying known, auditable rules |
| Fuzzy title, location, and description matching | Suggestive rather than conclusive | Similar roles may be separate requisitions, especially across locations | Fallback when stable identifiers are unavailable; use a score and review threshold |
| Provider exclusion or discovery filters | Useful for avoiding previously seen records in later calls to that provider | Provider-specific filters do not necessarily collapse different records for the same requisition | Reduce repeat results across recurring queries, alongside local cross-source deduplication |
A 2024 preprint reports improved duplicate detection from combining overlap-based character similarity, text embeddings, and curated weighted skill lists rather than relying on any one approach. It does not establish a universal threshold or a numerical performance result in the abstract, so treat combined similarity as a ranking signal—not proof that two records are identical. Read the paper abstract.
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Keep requisition identity separate from source-posting identity
A requisition-level ID answers, “Which opening is this?” A board’s job ID answers, “Which record did this provider return?” Preserve both, along with the source name, normalized apply URL, retrieval time, and the evidence behind any grouping. That lets you display one vacancy while retaining links back to every source record, investigate incorrect merges, and update a cluster if a listing changes.
Do not assume that a canonical URL solves every deduplication problem. Google’s job-posting guidance recommends canonical URLs for copies of a posting and structured data on the page describing a single job. That guidance concerns indexing and search presentation; it is not a universal database key for job-search clients. Google’s Job Posting documentation.
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Handle retries and repeated searches separately
Prevent duplicate writes after a retry
Idempotency addresses repeated submission of the same operation, not copies of a vacancy from different boards. SEEK’s developer guidance says to reuse the same idempotencyId when retrying the same posting and not reuse it for a different job. Its duplication documentation is marked draft, so details may change. See SEEK’s job ad duplication guidance.
Reduce repeats across calls to one provider
TheirStack documents discovered_at_gte and job_id_not as ways to avoid receiving previously returned jobs on later calls. Those are TheirStack-specific API filters; they can help with recurring queries but do not necessarily merge different provider records that refer to one requisition. TheirStack’s API documentation.
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Choose conservative merge rules
False merges can hide genuinely different openings. Two listings may share an employer, similar descriptions, or even a title while differing by location or requisition. Use a hierarchy rather than one universal comparison:
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- Group automatically when a validated, appropriately scoped requisition ID matches.
- Use normalized URL and employer evidence when no explicit shared ID is available, and retain the evidence for inspection.
- For fuzzy matches, combine title, location, and description signals; treat conflicting locations or requisition evidence as a reason not to merge automatically.
- Keep clusters reversible, with source records and match reasons visible to the user.
- When several links appear to represent the same active opening, the example’s author recommends preferring the employer-hosted ATS link over an aggregator mirror. Check that it is active and truly represents the same requisition; this is a practical recommendation, not a guarantee for every listing.
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