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Harwell compiles and runs mainframe estate code on a hosted runtime you call over MCP: you send the code, and Harwell returns what a mainframe would have shown you.
  • Batch. Submit JCL jobs: steps, DD statements, return codes, SORT and the common utilities, cataloged procedures, and chains of jobs with dependencies and one clock.
  • Online. Start CICS transactions from the PCT. Screens are typed one attention key at a time, BMS mapsets are assembled from their macro source, and the COMMAREA carries state from task to task.
  • Db2. Run EXEC SQL in batch and online programs, including SQL in CALLed subprograms. Query the tables afterwards with read-only SQL.
  • Data sets. Sequential, fixed and variable record formats, VSAM KSDS and RRDS, GDGs. List a run’s catalog and read records raw or through a copybook.
  • Codebases in place. Run a whole estate by its repository, ref and path, or by a tree you send. Programs, copybooks and procedures are found through the search order the codebase declares.
  • Terminals. Open a browser 3270-style screen for a person to drive a transaction by hand, then read back what they pressed.
  • Systems. Keep a named mainframe state across calls, with its data sets, tables and queues. Checkpoint it and restore it.
Every result opens with a one-line verdict, then the compiler listing, the job log or the screens, and links to the full report, every listing and every spool file.

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Endpoint

A streamable HTTP MCP server. See Connect an MCP server.

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Next

  • Quickstart: compile and run a COBOL job in a few minutes.
  • Concepts: mainframe terms mapped to what you know from distributed systems.
  • Tools: every tool, its parameters and the scope it needs.