M Code

A real M editor inside VS Code, with standard-library autocomplete, inline diagnostics, interactive Applied Steps that write genuine M for you, and an incremental-refresh setup form. Author your queries here, and let your Claude edit the same partition M over MCP.

#In the Studio

The M Code tab has two lanes: M query (the editor) and Incremental Refresh (a form over the refresh policy). The editor is CodeMirror with M syntax highlighting, offline formatting, a validity strip and Save.

Autocomplete and hover types are backed by the full M standard library (866 symbols: Table.*, List.*, Text.*, Sql.Database and the rest), vendored from Microsoft's open-source M language tooling and running entirely in the webview. Inline diagnostics squiggle syntax errors and duplicate identifiers as you type.

A transform bar and per-column menus write M for you: Remove, Rename, Change type, Filter rows, Replace values, Sort, Trim & Clean, Remove duplicates, and Keep top N. Each choice appends a correctly quoted step to the partition's M, and every generated step is parsed offline before it is written, so invalid M never lands. The Applied Steps outline is interactive: rename a step and every reference to it updates, delete one with re-point-to-predecessor semantics, or click a step to select its span in the editor. A profiling strip shows distinct and null counts and validity bars per column, badged as profiled from loaded data, and you can Duplicate or Reference a shared expression.

#Over MCP

The partition M, shared expressions and refresh policy are all dual-drive:

• list_partitions lists a table's partitions; get_partition_m reads a partition's M source and set_partition_m replaces it (both undoable and broadcast to the tab).
• Shared, model-level M expressions and parameters are first-class: list_named_expressions, get_named_expression, create_named_expression and update_named_expression. The RangeStart and RangeEnd parameters show up here.
• For incremental refresh, get_incremental_refresh_policy reads the policy, set_incremental_refresh_policy defines or updates it, and remove_incremental_refresh_policy clears it. list_refresh_types explains every process option (Full, DataOnly, Calculate, ClearValues and the rest) in plain language.

list_partitions  table:Sales            # -> each partition's ref + mode
get_partition_m  <partition ref>        # -> the M source expression
set_partition_m  <partition ref>  "let Source = Sql.Database(...) in Source"
get_incremental_refresh_policy  table:Sales     # -> store N periods, refresh last M

#Incremental refresh, set up safely

The Incremental Refresh lane is a form over the same policy API, with a live prerequisite checklist. Setting a policy is metadata only: it configures the refresh policy and never triggers a data load. The prerequisites are validated up front (the two parameters named RangeStart and RangeEnd, and a partition whose M actually filters the date column on them), so a policy is either complete or refused, never half-applied. On an existing policy you can change one knob and the rest is preserved.