Hopper – Agentic TN3270 Emulator for Mainframe AI

TL;DR

TL;DR: Hopper is an AI-native TN3270 terminal emulator that lets agents autonomously navigate ISPF, write JCL, debug batch jobs, and query z/OS datasets — turning decades-old mainframe operations into programmable, agentic workflows.

What Is Hopper?

Hopper is the first agentic development environment purpose-built for mainframes, developed by Hypercubic. Where traditional terminal emulators are human-facing tools, Hopper treats the mainframe as a programmable target — AI agents interact with it through the same TN3270 protocol that enterprise systems have used since the 1970s.

The product is a desktop app (macOS, Linux, Windows) with an embedded AI agent layer. Instead of manually navigating ISPF panels, engineers issue natural-language commands — “show me the output of job JOB1234” or “find all datasets matching SYS1.*” — and the agent handles the panel navigation, form filling, and data extraction.

Key capabilities, as listed on the product page:

• Autonomous ISPF navigation — agents traverse menus, allocate datasets, and run utilities without human mediation
• JCL authoring and submission — agents construct and submit Job Control Language scripts
• JES job monitoring — track job status, output, and error conditions across the JES spool
• Incident triage with RACF and SMF data — query security events and system measurement data
• COBOL compile and run — full compilation workflow inside the emulator
• CICS transaction tooling — interact with CICS regions
• TLS-secured TN3270 — encrypted connections to mainframe endpoints
• Mainframe MCP integration — connects to Model Context Protocol-compatible agent frameworks

Why This Matters for the Developer Tooling Landscape

Mainframes run a disproportionate share of global business logic. According to IBM, there are trillions of lines of COBOL still in production, and most Fortune 500 companies process millions of transactions per day through z/OS. Yet the tooling ecosystem for automating mainframe operations has been largely stagnant — dominated by green-screen interfaces that require years of institutional knowledge to operate.

Hopper’s bet is that the recent advances in AI agent capabilities have finally made mainframe automation viable without deep domain expertise. An agent that can reliably navigate a 3270 terminal can be applied to any legacy system that exposes a text-based interface — a category that includes far more than mainframes.

Setup Workflow

Prerequisites

• A z/OS system with TN3270 access (or a development mainframe like MVS 3.8j running under Hercules)
• Hopper app installed (free Hobby tier available)
• Optional: MCP-compatible agent framework for programmatic control

Step 1: Install Hopper

Download binaries from the official site:

# macOS (Apple Silicon)
curl -fsSL https://get.hopper.sh/mac-arm64.dmg -o hopper.dmg

# macOS (Intel)
curl -fsSL https://get.hopper.sh/mac-x64.dmg -o hopper.dmg

# Linux
curl -fsSL https://get.hopper.sh/linux-amd64.deb -o hopper.deb
# or
curl -fsSL https://get.hopper.sh/linux-x86_64.AppImage -o hopper.AppImage
chmod +x hopper.AppImage

# Windows
curl -fsSL https://get.hopper.sh/win-x64.exe -o hopper.exe

The current stable version is 1.4.0, released August 2026.

Step 2: Connect to a Mainframe

Launch the app and configure a connection profile:

Host:    your.mainframe.example.com
Port:    992 (TLS) or 23 (non-TLS)
LU name: YOUR.LU

TLS is enabled by default and recommended for all production connections.

Step 3: Issue Your First Agent Command

In the Hopper command bar, type a natural-language request:

Find all datasets matching SYS1.* in catalog TESTCAT

The agent navigates ISPF, issues the appropriate Datasets Utility commands, and returns a structured list of matching datasets with their attributes.

Step 4: Integrate with MCP

For programmatic use, connect Hopper to an MCP-compatible agent framework. The MCP server exposes tools structured as JSON:

{
  "tool": "jcl_submit",
  "parameters": {
    "jcl": "//JOB1   JOB (ACCT),'AGENT RUN',CLASS=A\n//STEP1  EXEC PGM=IEFBR14"
  }
}

Practical Evaluation Checklist

Core functionality:

• Does the agent reliably navigate multi-panel ISPF menus?
• Is JCL authoring context-aware (aware of dataset naming rules, catalog structures)?
• Does the job monitoring track JES2/JES3 spool output correctly?
• Are errors surfaced with enough context to triage without reading SMF raw data?

Security:

• Are TLS connections enforced by default?
• Is there RACF/ACF2 authority checking before actions?
• Does the Hobby tier restrict mainframe targets, or is it open to any TN3270 endpoint?

Developer experience:

• Is the MCP interface well-documented?
• Are there existing integrations with popular agent frameworks (LangChain, LlamaIndex, CrewAI)?
• Does the app expose a REST or gRPC API for non-MCP integrations?

Operational:

• Does the Hobby tier require a credit card?
• What is the pricing for team/org tiers?

Security Notes

Hopper operates as a man-in-the-middle agent between the user and the mainframe. When evaluating this tool for production use, consider:

1. Credential handling — TN3270 credentials are sent to the Hopper process; verify how credentials are stored and whether they leave the local machine
2. Audit trails — confirm that all agent actions are logged with user identity for RACF/ACF2 audit compliance
3. Network posture — TLS is supported; verify your mainframe is configured to reject non-TLS connections
4. MCP authentication — if connecting to an external agent framework over MCP, ensure the connection uses mutual TLS or a private network path

FAQ

Q: Do I need an actual mainframe to try Hopper? A: Yes — Hopper is a genuine TN3270 emulator. It requires a real z/OS system to connect to. You cannot simulate mainframe interactions locally.

Q: What is the free tier limitation? A: The Hobby tier is free with no credit card required. See the pricing page for specifics on connection limits or feature gates.

Q: Is this related to the Hopper compiler infrastructure project? A: No. This Hopper is a standalone product from Hypercubic, unrelated to the LLVM-based compiler infrastructure project of the same name.

Q: Can Hopper be used for production mainframe operations? A: Hypercubic offers custom enterprise pricing. Production use should be evaluated against your mainframe team’s existing change management and audit requirements.

Q: Does Hopper work with Windows-based mainframes or only z/OS? A: Hopper targets the TN3270 protocol used by z/OS, z/VSE, and z/VM. It does not support 3270 connections to IBM i (AS/400) or other non-zSeries platforms.

Source and Accuracy Notes

⚠️ This section is MANDATORY. All links must be verified from actual source, not guessed.

• Project page: hyperbolic.ai/hopper
• Company: Hypercubic — Y Combinator backed, founded 2025
• License: Proprietary (free Hobby tier available)
• HN launch thread: news.ycombinator.com/item?id=43725306 — 97 points
• Source last checked: 2026-08-23 (product page, YC company page)