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How to Build Candidate Assessments Across Workday, Greenhouse, Lever, and 60+ ATS Platforms with a Unified API

September 28, 2025

Candidate assessment is a core step in hiring. Once an application reaches a defined stage—like 'Reviewing' in an ATS—your product may need to trigger an assessment, collect results, and push them back to the ATS.

Doing this across dozens of applicant tracking systems (ATS) is where most teams hit friction. Each ATS has its own schema, authentication, and webhook behavior. A unified API removes that complexity by providing normalized candidate, application, job, and attachment data in real time—plus write support for posting results back.

This same ingestion pattern also enables retrieval-augmented generation (RAG), where resumes and job descriptions are embedded and retrieved at query time to power ranking, matching, and AI-generated evaluations.

Why Candidate Assessment Requires Integrations

ATS platforms are the system of record for candidate and job data. To power assessments, your application needs:

  • Candidate profile and contact details
  • Application status and job context
  • Attachments like resumes or portfolios
  • Power semantic matching between resumes and job descriptions using a RAG pipeline built on ATS data

Assessments often need to be triggered automatically, then scored results written back as notes, custom fields, tags, or stage changes. Without a unified API, you'd build and maintain custom integrations for each ATS vendor—slowing roadmap delivery and creating long-term maintenance overhead.

Normalized Candidate Data

A unified API standardizes the core ATS objects:

  • Application (ats_application): links candidate to job (id, status, stage, created_at).
  • Candidate (ats_candidate): profile and contact data (id, name, emails, resume_url).
  • Job (ats_job): requisition record (id, title, department, location).
  • Attachment (ats_attachment): resumes, portfolios, or supporting files (id, file_url, mime_type).

Webhooks—native or virtual—stream changes in real time, so assessments can be triggered at the right stage.

Data Flow for Assessments

With Unified.to, the flow is straightforward:

  1. Connect the ATS via Unified Connect.
  2. Fetch ats_application records and filter by status to identify candidates to assess.
  3. Register a webhook for application updates—Unified manages native and virtual streams.
  4. Retrieve related candidate, job, and attachment records for context.
  5. Run your assessment workflow.
  6. Write results back to the ATS as notes, tags, stage updates, or attachments.

This enables your product to deliver a consistent assessment experience across ATS platforms without custom code per vendor.

Want a deeper dive into implementation patterns? Check out our guide: How to Build a Candidate Assessment Product with Unified.to

Extending Candidate Assessments into a RAG Pipeline

For AI-driven screening, ranking, or recruiter Q&A, extend this workflow into a RAG architecture:

  1. Subscribe to application create/update webhooks.
  2. Retrieve resumes and job descriptions via ats_attachment and ats_job.
  3. Chunk resume and job text and generate embeddings.
  4. Store embeddings in your vector database with identifiers like connection_id, candidate_id, job_id, and updated_at.
  5. On evaluation, retrieve the most relevant resume segments against the job description before generating scores or written feedback. Unified Use Case RAG Pipelines

Unified handles real-time ingestion across 63+ ATS platforms; you manage embeddings and vector storage in your own infrastructure.

Supported ATS Platforms

Unified.to supports 63+ ATS integrations, including leading systems like:

  • Workday
  • SuccessFactors
  • ADP Workforce Now
  • Greenhouse
  • Lever
  • iCIMS
  • Ashby
  • SmartRecruiters
  • Jobvite
  • Bullhorn
  • BambooHR
  • Workable
  • UKG Pro ATS

See the full list of supported ATS integrations

Why This Matters for Product Teams

For PMs and platform engineers, the value is direct:

  • Trigger assessments consistently across 63+ ATS systems without custom logic.
  • Unify candidate and job data into a single schema—making it easier to build RAG-based resume search, semantic matching, and AI-driven screening.
  • Push outcomes back in real time—ensuring recruiters see results immediately.
  • Scale without maintenance—no need to manage tokens, retries, or API changes.

Start building candidate assessment workflows across 63+ ATS platforms today. Sign up for a free 30-day trial or book a demo to see how Unified.to can support your roadmap.

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