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Justworks MCP Server
for AI Agents

Connect your AI agent to StackOne's Justworks MCP server and give it 21 MCP tools out of the box. Auth, tool execution, and security all managed.

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Justworks MCP Server
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Coverage

21 Agent Actions

Create, read, update, and delete across Justworks — and extend your agent's capabilities with custom actions.

MCP Actions → Build Actions →

Authentication

Agent Tool Authentication

Per-user OAuth in one call. Your Justworks MCP server gets session-scoped tokens with zero credentials stored on your infra.

Agent Auth →

Security

Agent Protection

Every Justworks tool response scanned for prompt injection in milliseconds — 88.7% accuracy, all running on CPU.

Prompt Injection Defense →

Performance

Max Agent Context. Min Cost.

Free up to 96% of your agent's context window to enhance reasoning and reduce cost, on every Justworks call.

Tools Discovery →

What is the Justworks MCP Server?

A Justworks MCP server lets AI agents read and write Justworks data through the Model Context Protocol — Anthropic's open standard for connecting LLMs to external tools. StackOne's Justworks MCP server ships with 21 pre-built actions, fully extensible via the Connector Builder — plus managed authentication, prompt injection defense, observability, and agent execution runtime. Connect it from MCP clients like Claude Desktop, Claude Code, Cursor, Goose, and VS Code, or from agent frameworks like OpenAI Agents SDK, LangChain, and Vercel AI SDK.

All Justworks MCP Tools

Every action from Justworks's API, ready for your agent. Create, read, update, and delete — scoped to exactly what you need.

Members

  • List Members

    Retrieve a paginated list of company members (employees and contractors).

  • Get Member

    Retrieve a specific member by their ID.

Deductions

  • Create Deductions

    Create new deductions for company members.

  • List Deductions

    Retrieve a paginated list of deductions.

  • Update Deductions

    Update existing deductions.

Time Off Balances Reports

  • Create Time Off Balances Report

    Create a new time off balances report.

  • Get Time Off Balances Report

    Retrieve a previously created time off balances report.

Other (14)

  • Get Company

    Retrieve company information including name, addresses, departments, and offices.

  • Get Company Bank Account

    Retrieve company bank account details.

  • Get Company Business Info

    Retrieve company business information including entity identifiers and officers.

  • List Company Custom Fields

    Retrieve all custom fields defined for the company.

  • List Company Jurisdictions

    Retrieve all jurisdictions where the company operates.

  • List Member Custom Field Values

    Retrieve custom field values for a specific member.

  • List Payrolls

    Retrieve a paginated list of payrolls.

  • List Payroll Fees

    Retrieve fees associated with a specific payroll.

  • List Payroll Paystubs

    Retrieve paystubs for a specific payroll.

  • Get Paystub

    Retrieve a specific paystub by its ID.

  • List Deduction Types

    Retrieve all available deduction types.

  • List Time Off Policies

    Retrieve a paginated list of time off policies.

  • List Time Off Requests

    Retrieve a paginated list of time off requests.

  • Cancel Deductions

    Cancel existing deductions.

Justworks AI Agent Use Cases

Connect your AI agent to Justworks and help your team scale the HR operations they run by hand today.

Employee Onboarding

Use StackOne to connect your AI agent to your HRIS, identity management, and LMS to automate employee onboarding.

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WorkdayBambooHRPersonioHiBobGustoRipplingOkta360Learning
HR Policy Q&A Chatbot

Use StackOne to connect your AI agent to your HRIS, knowledge base, and messaging tools to automate HR policy Q&A.

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WorkdayBambooHRPersonioHiBobGustoRipplingSharePointConfluence
Employee Offboarding

Use StackOne to connect your AI agent to your HRIS, identity management, and ITSM to automate employee offboarding and deprovisioning.

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WorkdayBambooHRPersonioOktaServiceNowRipplingGustoJira
More HRIS & HCM use cases

Set Up Your Justworks MCP Server in Minutes

One endpoint. Any framework. Your agent is talking to Justworks in under 10 lines of code.

MCP Clients

Claude Desktop setup guide
Claude Code setup guide
Cursor setup guide
Goose setup guide

Agent Frameworks

Claude Desktop
{
  "mcpServers": {
    "stackone": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote@latest",
        "https://api.stackone.com/mcp?x-account-id=<account_id>",
        "--header",
        "Authorization: Basic <YOUR_BASE64_TOKEN>"
      ]
    }
  }
}

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Platform Resources

MCP Code Mode: Keeping Tool Responses Out of Agent Context

Anthropic's code_execution processes data already in context. Custom MCP code mode keeps raw tool responses in a sandbox. 14K tokens vs 500.

11 min

Comparing BM25, TF-IDF, and Hybrid Search for MCP Tool Discovery

Benchmarking BM25, TF-IDF, and hybrid search for MCP tool discovery across 916 tools. The 80/20 TF-IDF/BM25 hybrid hits 21% Top-1 accuracy in under 1ms.

10 min

Indirect Prompt Injection Defense for MCP Tools: A Technical Guide

MCP tools that read emails, CRM records, and tickets are indirect prompt injection vectors. Here's how we built a two-tier defense that scans tool results in ~11ms.

12 min

MCP vs A2A: Architecture, Security, and When to Use Each

MCP vs A2A: what each protocol standardizes, how they differ, their shared security risks including indirect prompt injection, and when to use one, both, or a hybrid architecture.

12 min

MCP vs API: What 200+ Connector Builds Taught Us

MCP wraps APIs, it doesn't replace them. After building 200+ connectors that serve both, here's when each approach wins.

14 min read

Justworks MCP Server FAQ

Does StackOne have a Justworks MCP server?
Yes. StackOne offers a hosted Justworks MCP server with 21 pre-built actions, and every action is tested and QA'd by StackOne. Connect it to Claude, Cursor, and any other MCP client, or to any agent framework through the AI Action SDK. It ships with managed agent authentication, prompt injection defense, and tool discovery with server-side execution that preserve your agent's context window and keep reasoning performance.
Justworks MCP server vs direct API integration — what's the difference?
A Justworks MCP server and direct API integration serve different use cases. Direct API integration is for software-to-software — backend code calling Justworks. A Justworks MCP server is for AI agents — MCP clients like Claude and Cursor, plus framework agents built with OpenAI, LangChain, or Vercel AI — discovering and calling Justworks at runtime. StackOne provides both.
How does Justworks authentication work for AI agents?
Justworks authentication for AI agents works through a StackOne Connect Session. Create one via the dashboard or the SDK — you get an auth link and ready-to-paste config for Claude Desktop, Cursor, and other MCP clients. Your user authenticates their own Justworks account; StackOne handles token exchange, storage, and refresh. Credentials never reach the LLM, and each user is isolated via origin_owner_id.
Are Justworks MCP tools vulnerable to prompt injection?
Yes — Justworks MCP tools can be vulnerable to indirect prompt injection. Any tool that reads user-written content — documents, messages, tickets, records, or free-text fields — is a potential vector. StackOne Defender scans every tool response before it enters the agent's context — regex patterns in ~1ms, then a MiniLM classifier in ~4ms. 88.7% accuracy, CPU-only.
What is the context bloat of a Justworks agent and how do I avoid it?
Context bloat happens when Justworks tool schemas and API responses eat your Justworks agent's memory, preventing it from reasoning effectively. A single Justworks query can return a massive JSON response, and connecting multiple tools compounds the problem. Tools Discovery and Code Mode reduce context bloat — loading only relevant tools per query and keeping raw responses out of the agent's context.
Can I limit which actions my Justworks agent can access?
Yes — you can limit which actions your Justworks agent can access directly from the StackOne dashboard. Toggle actions on or off, or restrict them to specific accounts, with no code changes to your agent. Session tokens can be scoped to exact actions so if one leaks, exposure stays contained.
Can I create custom agent actions for my Justworks MCP server?
Yes — you can create custom agent actions for your Justworks MCP server using Connector Builder. It's an integration agent your coding assistant (Claude Code, Cursor, or Copilot) can invoke to research Justworks's API, generate production-ready connector YAML, test against the live API, and validate before you ship.
When should I NOT use a Justworks MCP server?
Skip a Justworks MCP server if your integration is purely software-to-software — direct Justworks API integration is simpler when no AI agent is involved. For deterministic, compliance-critical operations (financial transactions, regulatory reporting), direct API gives you predictable behavior without agent-driven decision-making. MCP shines when AI agents need to dynamically discover and call Justworks actions at runtime.
What AI frameworks and AI clients does the StackOne Justworks MCP server support?
The StackOne Justworks MCP server supports both. MCP clients (paste-and-go apps): Claude Desktop, Claude Code, Cursor, VS Code, Goose. Agent frameworks (code SDKs you build with): OpenAI Agents SDK, Anthropic, Vercel AI, Google ADK, CrewAI, Pydantic AI, LangChain, LangGraph, Azure AI Foundry.

Put your AI agents to work

All the tools you need to build and scale AI agent integrations, with best-in-class connectivity, execution, and security.

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