JA Technology Solutions
BMS Screen Explorer
Paste mainframe BMS (CICS/3270) screen definitions and see the screen rendered with green-screen and modern preview.
BMS Screen Explorer
Upload or paste mainframe BMS (Basic Mapping Support) screen definitions used in CICS applications and see the screen layout rendered in your browser. Toggle between an authentic 3270 green-screen preview and a modern position-aware HTML layout. View the complete field layout with row and column positions, lengths, and attributes (protected, bright, dark, numeric), plus map-level DFHMSD and DFHMDI properties — map set name, map names, screen dimensions, and control settings at a glance. Parses DFHMSD, DFHMDI, and DFHMDF macros with line continuation support and exports the field layout to CSV or Excel for documentation and modernization planning. Runs entirely in your browser — your source never leaves your machine.
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What Are BMS Screen Definitions?
BMS (Basic Mapping Support) is the screen definition language for CICS (Customer Information Control System) applications on IBM mainframes. BMS macros — DFHMSD (mapset), DFHMDI (map/screen), and DFHMDF (field) — define the layout of 3270 terminal screens used by CICS programs. Each field definition specifies a row/column position, length, attributes (protected, unprotected, numeric, bright, dark), and initial values. BMS source uses assembler-style syntax with line continuations, making it difficult to read without rendering the actual screen layout.
Why Visualize BMS Screens?
Like DDS display files on IBM i, raw BMS source describes screen layouts in coordinate-based field definitions that are hard to visualize mentally. This tool parses the BMS macros, resolves line continuations, and renders the screen as both an authentic 3270 green-screen preview and a modern HTML layout. This is invaluable for documenting existing CICS applications, planning modernization projects, training new developers on legacy systems, and comparing screen layouts during redesign efforts without needing access to a running mainframe.
Mainframe Modernization
Organizations modernizing CICS applications often start by cataloging and documenting existing BMS screens to understand the user interface before redesigning it for web or mobile delivery. I help plan and execute mainframe modernization projects, from initial screen inventory and analysis through modern interface design and implementation. Whether you are wrapping CICS transactions with APIs, building web front-ends, or migrating off the mainframe entirely, learn about modernization services, explore migration capabilities, or get in touch.
All tools run entirely in your browser. Your data never leaves your machine. Need help? Ask James.