marlinfirmware/marlindocumentation/gcode-page

Add or update a G-code page

Each command has one page in docs/gcode/, named by zero-padded code: G000-G001.md, G029.md, M851.md. Variants of one code get a suffix (G029-ubl.md, G029-mbl.md) and the base page lists them. All structured data lives in the frontmatter; _layouts/gcode.html renders it. Only the description goes in the body.

Frontmatter data model

---
tag: m0851                        # lowercase letter + 4-digit code; anchor prefix in the Usage section
title: "M851: XYZ Probe Offset"   # "CODE: Short Title" — this is the sidebar text
short_title: XYZ Probe Offset
brief: Set the Z probe XYZ offset from nozzle
author: thinkyhead
parent: G-code Commands           # every page
group: calibration                # motion, calibration, temperature, sdcard, units, geometry, control, eeprom, debug, trinamic, ...
since: 2.0.0                      # first release that has the command
requires: HAS_BED_PROBE           # config flag (optional); experimental: true; eeprom: true
codes: [ M851 ]                   # always an array
related: [ G29, M500 ]            # optional
notes: |                          # string or list; markdown allowed
  ...
parameters:
- tag: Z
  optional: true
  description: Z probe offset from the nozzle
  values:
  - tag: offset
    type: float
examples:                         # `example:` singular is also accepted
- pre: Set the Z offset
  code: M851 Z-1.5
  post: Then save with M500
---

Steps

1. Verify the command in the source, never from the number: Marlin/src/gcode/gcode.cpp dispatch and the

handler file under Marlin/src/gcode/<category>/. Parameters come from parser.seen*() calls in the handler.

1. Find `since` by checking the source at each release tag:

git show 2.0.0:Marlin/src/gcode/gcode.cpp | grep 'case 851:' (use Marlin/Marlin_main.cpp before 2.0; for a G-code grep the handler name, since case 80: also matches M80). Don't use git tag --contains.

1. Write or edit the page. Keep the data model; do not move parameters or examples into prose.
2. Regenerate the index: python3 _tools/gen_gcode_index.py (rewrites docs/gcode/index.md from frontmatter).
3. Check: python3 _tools/check_site.py && bundle exec jekyll build && python3 _tools/check_links.py && python3 _tools/check_feed.py.

The feed check matters here: the Auto Build Marlin extension reads one entry per G-code page.

1. Sanity-check the rendered page: header badges (group, since, requires), Usage block, Parameters, Examples.

Pitfalls

• A tag/codes mismatch or a missing parent: drops the page from the sidebar and the index.
• requires: values starting with ! must be quoted ("!NO_VOLUMETRICS").
• Pages with pagetype: toc are navigation stubs for variants; they carry no parameters.
• The same G-code number can mean something else in other firmware (RepRap wiki); document Marlin's behavior only.