Variables & Evaluation

The viewport shows a shallow snapshot of local variables at every stop. Use debug_variables and debug_evaluate to go deeper when you need it.

Viewing Variables

CLI

# Locals (default)
krometrail vars

# All scopes
krometrail vars --scope all

# Global scope
krometrail vars --scope global

# Closure variables
krometrail vars --scope closure

# Filter by name prefix
krometrail vars --filter "^user"

# Different stack frame
krometrail vars --frame 2

MCP: debug_variables

// Locals
{ "session_id": "...", "scope": "local" }

// All scopes
{ "session_id": "...", "scope": "all" }

// With regex filter
{ "session_id": "...", "scope": "local", "filter": "^user" }

// Expand objects deeper
{ "session_id": "...", "scope": "local", "max_depth": 3 }

// From a different frame
{ "session_id": "...", "scope": "local", "frame_index": 2 }

Parameters

Parameter	Type	Default	Description
scope	string	"local"	"local", "global", "closure", or "all"
frame_index	integer	0	Stack frame (0 = current, 1 = caller, etc.)
filter	string		Regex filter on variable names
max_depth	integer	1	Object expansion depth

Evaluating Expressions

debug_evaluate is the primary drill-down tool. Use it to inspect nested objects, call methods, compute derived values, or test hypotheses — without modifying the code.

CLI

# Simple expression
krometrail eval "discount"

# Method call
krometrail eval "cart.total()"

# Dict/object access
krometrail eval "tier_multipliers['gold']"

# Deep object expansion
krometrail eval "user.__dict__" --depth 3

# In a different frame
krometrail eval "request.headers" --frame 2

MCP: debug_evaluate

// Simple
{ "session_id": "...", "expression": "discount" }

// Deep expansion
{ "session_id": "...", "expression": "cart.__dict__", "max_depth": 3 }

// Caller's frame
{ "session_id": "...", "expression": "request.headers", "frame_index": 2 }

Parameters

Parameter	Type	Default	Description
expression	string		Expression to evaluate
frame_index	integer	0	Stack frame context
max_depth	integer	2	Object expansion depth

Value Rendering

Variable values are rendered consistently across all languages:

Type	Rendering
Primitives	Displayed as-is: 149.97, true, None
Strings	Quoted, truncated at 120 chars: "hello..."
Collections	Type + length + preview: [1, 2, 3, ... (47 items)]
Objects	Type + key fields: <User: id=482, tier="gold">
Expandable	Truncated values show a hint that debug_evaluate can expand them

Workflow: Hypothesis Testing

The most effective pattern is to form a hypothesis about a bad value, then use debug_evaluate to confirm or refute it without modifying code:

# Hypothesis: tier_multipliers has wrong value for gold
krometrail eval "tier_multipliers"
# → {"bronze": 0.05, "silver": 0.1, "gold": 1.0, "platinum": 0.2}
# Confirmed: gold should be 0.1, not 1.0

# Hypothesis: the calculation is done correctly but the result has wrong sign
krometrail eval "calculate_discount(user, 100.0)"
# → -100.0 (confirms the sign is inverted in the multiplier application)

Evaluate expressions to test hypotheses at the current stop before deciding whether to step further.