> ## Documentation Index
> Fetch the complete documentation index at: https://hub.stackone.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Unified ATS API
> Unified ATS API that standardizes recruitment workflows across platforms with consistent data models for candidate management, job postings, and application tracking.
**Legacy documentation.** The Legacy Unified APIs are no longer in active development. Existing functionality remains supported, and no new features or enhancements will be added.
For the current StackOne platform, connectors, and agent tooling, see [docs.stackone.com](https://docs.stackone.com).
## What is a Unified API?
A **unified API** provides a single, standardized interface to interact with multiple third-party providers. Instead of learning each provider's unique API format, authentication scheme, and data model, you write code once, and StackOne handles the differences.
**What StackOne normalizes:**
* **Data models** – Consistent field names and structures across providers (e.g., `files` in Google Drive, SharePoint, and Dropbox all return the same schema; `users` in Google Workspace, Okta, and 1Password all return the same schema)
* **Authentication** – OAuth, API keys, and tokens are managed per-provider; you just pass an `x-account-id` header
* **Pagination** – Cursor-based pagination works the same regardless of whether the provider uses offsets, pages, or cursors
* **Error formats** – Standardized error responses with provider-specific details when available
**Building AI agents?** Use the [MCP Server](https://docs.stackone.com/embed/call-actions/mcp), an [AI Toolset SDK](https://docs.stackone.com/embed/call-actions/agent-sdk), or the [Actions API (RPC)](https://docs.stackone.com/platform/api-reference/actions/make-an-rpc-call-to-an-action) instead. Same data, optimized for LLM tool calling.
## Benefits of the ATS API
StackOne's APIs interfaces with the underlying systems in real-time, allowing for immediate updates and synchronization across platforms.
With a [focus on security](https://www.stackone.com/blog/why-your-choice-of-unified-api-could-make-or-break-compliance), StackOne's architecture avoids unnecessary data storage, maintaining compliance with data protection regulations.
The platform provides both [synthetic and native webhooks](/legacy-unified-apis/common-guide/webhooks), enabling real-time notifications for candidate and job posting changes.
StackOne offers [pre-built connectors](https://www.stackone.com/integrations) with a wide range of ATS platforms, simplifying the integration process.
## Key Features
The table below shows key features of the ATS API that make recruitment easier, from real-time application tracking and offer Management:
| **Feature** | **Description** |
| ---------------------------------- | --------------------------------------------------------------------------------------------------------------- |
| Comprehensive Candidate Management | Easily create, update, and retrieve candidate profiles, including personal information and application history. |
| Job Postings and Metadata | List and manage job postings, access detailed descriptions, compensation ranges, and related questionnaires. |
| Application Tracking | Monitor and update application statuses, manage interview stages, and handle offer details. |
| Real-Time Webhooks | Receive instant notifications for changes in data like - candidates, applications, or job postings. |
| Document Handling | Upload, download, and manage candidate documents such as resumes and cover letters. |
| Interview Scheduling | Record and manage interview details, including times, participants, and locations. |
| Offer Management | Handle job offers, track their status, and manage candidate responses efficiently. |
## StackOne SDKs & OpenAPI Specification
Use our official SDKs for faster integration. Build with language-native libraries. Full list [here](https://docs.stackone.com/platform-api/api-sdks).
[Node.js](https://www.npmjs.com/package/@stackone/stackone-client-ts)
[Java (JVM)](https://mvnrepository.com/artifact/com.stackone/stackone-client-java)
[PHP](https://packagist.org/packages/stackone/client-sdk)
[Ruby](https://rubygems.org/gems/stackone_client)
## Entity Model and Relationships
The following diagram illustrates the key entities within the ATS API:
```mermaid theme={null}
erDiagram
%% Main entities
Application {
string id
string candidate_id
string job_id
string job_posting_id
string interview_stage_id
array location_ids
}
Candidate {
string id
}
Job {
string id
array department_ids
array location_ids
}
%% Interview process entities
InterviewStage {
string id
}
Interview {
string id
string application_id
string interview_stage_id
}
Scorecard {
string id
string application_id
string interview_id
string candidate_id
string author_id
}
%% Offer and rejection entities
Offer {
string id
string application_id
}
RejectedReason {
string id
}
%% Assessment entities
AssessmentPackage {
string id
}
AssessmentOrder {
string id
string application_id
string candidate_id
}
BackgroundCheckPackage {
string id
}
BackgroundCheckOrder {
string id
string application_id
string candidate_id
}
%% Support entities
Department {
string id
}
Location {
string id
}
JobPosting {
string id
string job_id
}
Note {
string id
string author_id
}
User {
string id
}
List {
string id
}
%% Core hiring flow
Candidate ||--o{ Application : submits
Job ||--o{ Application : receives
JobPosting ||--o{ Application : attracts
%% Interview process
Job ||--o{ InterviewStage : defines
Application ||--o{ Interview : schedules
Interview }|--|| InterviewStage : follows
Interview ||--o{ Scorecard : evaluated_by
%% Outcome paths
Application ||--o{ Offer : may_receive
Application ||--o{ RejectedReason : may_have
%% Assessments
Application ||--o{ AssessmentOrder : undergoes
AssessmentOrder }|--|| AssessmentPackage : uses
Application ||--o{ BackgroundCheckOrder : undergoes
BackgroundCheckOrder }|--|| BackgroundCheckPackage : uses
%% Supporting relationships
Job }|--o{ Department : belongs_to
Job }|--o{ Location : based_in
Job ||--o{ JobPosting : advertised_as
Application }|--o{ Location : associated_with
User ||--o{ Note : writes
Application ||--o{ Note : has
Candidate ||--o{ Note : has
```
The following table outlines key entities within the ATS system and provides a brief description of each:
| Entity | Description |
| ------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| Applications | Manages job applications, including creation date, status, linked job and candidate identifiers, and more. |
| Application Offers | Handles job offers associated with applications, providing information on offer status, details, responses, and tracking from creation to acceptance or rejection. |
| Interviews | Records details of candidate interviews, including times, participants, and location (e.g., meeting URL). |
| Interview Stages | Represents different interview process stages, such as initial screening, technical rounds, and final interviews. |
| Rejected Reasons | Manages standardized reasons for candidate application rejections, aiding in consistent decision-making and recruitment process analysis. |
| Candidates | Provides detailed profiles of job candidates, including personal information, qualifications, application status, and history with the company. |
| Candidate Notes | Manages notes related to specific candidates, including content (usually simple text strings) and author. |
| Users | Manages user accounts within the ATS, including recruiters, HR personnel, and hiring managers, with access to user details, roles, and permissions. |
| Jobs | Manages job positions within the organization, including title, location, and status. |
| Job Postings | Focuses on the public aspect of the job, including extended descriptions, compensation ranges, and related questionnaires for applying. |
| Locations | Manages geographical locations associated with a job or job posting. |
| Departments | Manages organizational departments that jobs are associated with. |
| Scorecards | Tracks evaluations and feedback from interviewers about candidates, including ratings and comments. |
| Lists | Manages custom lists that can be used to group candidates, jobs, or other entities. |
| Assessment Packages | Defines assessment tests that candidates can take during the hiring process. |
| Assessment Orders | Records instances of assessments assigned to specific candidates. |
| Background Check Packages | Defines background check processes that candidates may undergo. |
| Background Check Orders | Records instances of background checks performed on specific candidates. |
| Notes | Manages notes that can be associated with various entities like applications, candidates, etc. |
## Use cases
Job boards can post positions, accept applications, and monitor candidate progress through normalized recruitment stages via a single API that handles the complete application lifecycle.
Interview intelligence platforms can access structured interview data, update scorecards, and analyze candidate performance across standardized evaluation criteria.
Screening solutions can retrieve applications, process candidate data through qualification algorithms, and update application stages with acceptance or rejection reasoning using standardized fields.
Providers can receive candidate evaluation orders, update test results, and automatically update application statuses with standardized scoring data that feeds directly into the hiring decision process.