Nomain for VS Code

Understand and change your mainframe systems without leaving the editor.

Nomain brings your System into VS Code. Ask how a program works and get an answer grounded in the code, with every reference one click from the source. Ask for a change and Nomain Code proposes edits that account for everything else that depends on it, and you review each one before it lands.

Nomain Code proposing a change to a COBOL program, the edit open for review, and the summary once it is applied

What it does

Nomain Code proposes changes you review. Ask for a change and the agent investigates your System, then proposes edits. In Review mode, the default, you accept or reject each file and each hunk, and every command asks before it runs.
Edits account for the whole System. A change is grounded in how the rest of your code depends on it, and you are warned when an edit touches a copybook that is used elsewhere.
Your files say what the System knows about them. Open an indexed COBOL, PL/I or JCL file and each construct shows its callers, dead stores, unreachable paragraphs and when it last changed, each with the agent action that follows from it. The eye button in the editor title bar hides them, and shows them again, in one click.
Answers cite the exact code. Ask a question and click a reference in the answer to open that file at the line it came from.
Bring what you are looking at into the question. Type @ to attach a file, or press Alt+K (Option+K on macOS) to attach the lines selected in the editor.
Your team's way of working comes with the code. Nomain Code reads the project's conventions from AGENTS.md or CLAUDE.md, and the skills it ships under .agents/skills/ or .claude/skills/. Type / to call a skill by name.
Pick up where you left off. Reopen any past conversation from the history, including one you started in the web app with Continue in VS Code.
Trace where a value comes from and where it goes. Put the cursor on a COBOL data item and click the lineage button in the Nomain header (or press Alt+Shift+L) to see who writes and reads it across the whole System, how its value flows statement by statement, and ask Nomain Code to explain it.
Private by design. Model calls go through your Nomain deployment, never from your editor straight to an AI provider.

Screenshots

Review every edit, file by file and hunk by hunk

The edit review in VS Code: a proposed change to a COBOL copybook, flagged as used by other programs

The proposed change in the chat, with Accept all, Reject all and Open diff

Choose how much you review

The approval-mode picker in the chat composer: Review every change, Auto-apply edits, and Auto + command grants

Ask about your code, and jump to the source

An answer about a COBOL program with clickable code references, next to the source file open in the editor

Call your project's skills by name

The slash menu in the composer, listing the project's skills

Requirements

VS Code 1.100 or later
A Nomain account with access to at least one System

Getting started

Install the extension and click the Nomain icon in the Activity Bar.
On the sign-in screen, click Configure Nomain and enter your Nomain address. Or choose Set up VS Code in the web app's user menu, which opens VS Code with the address filled in.
Click Sign In and confirm the sign-in code in your browser.
Pick a System and start asking.

The full guide is at docs.nomain.com.

Tracing data lineage

Place the cursor on a data item (for example ACCT-CURR-BAL). The lineage button in the Nomain header, left of Chat history, lights up while the cursor is on one; click it. You can also press Alt+Shift+L, right-click → Nomain: Trace Data Lineage, or run the command from the Command Palette. A lineage card appears in the Nomain sidebar with:

where the item is declared (copybook or program, level and picture);
every program and paragraph in the System that reads or writes it, from the knowledge graph — including repositories you do not have open;
the statements in your workspace that move its value in and out (MOVE, COMPUTE, ADD, CALL … USING, READ … INTO, SQL host variables…), each linked to its file and line, followed up to nomain.lineage.maxDepth hops;
a diagram of the flow, and an Explain with Nomain Code button that hands the report to the agent for the business meaning and change risks.

Graph data reflects the last analysis; statement lines come from the live files.

Configuration

All settings are under Nomain in VS Code Settings.

Setting	Description	Default
`nomain.serverUrl`	The address of your Nomain deployment.	Set from the sign-in screen, or by Set up VS Code
`nomain.agent.sessionLog.enabled`	Keep a copy of each Nomain Code conversation on this computer, so a conversation you reopen carries on with the agent's own notes. The copy never leaves this computer.	`true`
`nomain.agent.reasoningEffort`	How much Nomain Code reasons on each turn: `off`, `minimal`, `low`, `medium` or `high`. Higher is more thorough and slower. Takes effect in the next conversation.	`high`
`nomain.lineage.maxDepth`	How many value-flow hops Trace Data Lineage follows through the COBOL in your workspace, from `0` to `4`.	`2`

Commands

Command	Description
Nomain: Sign In	Sign in through your browser
Nomain: Sign Out	Clear the stored session
Nomain: Configure Server URL	Change the Nomain deployment the extension connects to
Nomain: Add Selection to Chat Context	Attach the lines selected in the editor (`Alt+K`)
Nomain: Stop Generating	Stop the answer in progress (`Esc Esc`)
Nomain: Send Feedback	Send a Proposal, Problem or Compliment to the Nomain team
Nomain: Clear Local Sessions	Delete the conversation copies kept on this computer
Nomain: Trace Data Lineage	Show the lineage of the COBOL data item under the cursor (`Alt+Shift+L`)

Support

Contact your Nomain account team, or email support@nomain.com. Release notes are bundled with the extension as CHANGELOG.md.

License

Nomain Proprietary License. For licensing inquiries, contact support@nomain.com.