g-eskayo/marvin/variable-tracker

Variable Tracker Skill

Find where a Python variable is defined, where it's used, and what scope it belongs to — without reading the whole file.

Triggers

Load this skill when you're:

• "track this variable" / "where is X defined/used"
• Starting work on an unfamiliar Python file
• Asking "what's the state of X" — did we mutate it, is it stale?
• Debugging variable shadowing or scope issues

CLI usage

# After running install.sh:
track-vars <path> [<path>...]                    # scan file(s) or dir(s)
track-vars <path> --name X                       # find variable X only
track-vars <path> --since HEAD~1                 # only files changed since commit
track-vars <path> --format json                  # JSON output for piping

Output format

Default text output: compact, inline-friendly, meant to paste into conversation:

cfg    [module]    lib/config.py    (dict)
  def    L12    cfg = load_config()
  use    L15    return cfg["timeout"]
  use    L30    log_config(cfg)

Columns: variable name, scope, file, inferred type (if annotated). Each var tracks definitions (assignments, parameters, for/with targets) and uses (loads).

Same variable name in different scopes (e.g., x in module vs x in func1()) tracked separately — shadowing isn't conflated.

JSON output (--format json) suitable for tool chaining:

[
  {
    "name": "cfg",
    "scope": "[module]",
    "file": "lib/config.py",
    "definitions": [
      {"line": 12, "kind": "assign", "snippet": "cfg = load_config()"}
    ],
    "uses": [
      {"line": 15, "snippet": "cfg[\"timeout\"]"}
    ]
  }
]

Extraction logic

Python-only (v1). Walks the AST:

• Definitions: assignments, annotated assignments, augmented assignments (+=), for/with targets, function parameters, global/nonlocal declarations
• Uses: Name nodes in Load context (reading a var)
• Scope: module-level or function name; same var in different scopes tracked as separate records

Type annotations from x: int = 10 are captured.

Filters

• --name X: return only variable X across all scanned files/scopes
• --since <git-ref>: restrict scan to files changed since <ref> (via git diff --name-only)

Directory traversal

Recursively scans .py files; skips venv, node_modules, .git, __pycache__, .venv.

Install

bash ~/.agents/skills/variable-tracker/install.sh
source ~/.zshrc

Then use track-vars from anywhere in the repo.