Ue Live Debugging

UE Live Debugging

Rider MCP debugging workflow: find the suspect symbol, trace who calls it, see what the IDE already knows is wrong.

GATE — mandatory checks before any debugging work

1. UE Project Check

Verify the current working directory contains a .uproject file:

find . -maxdepth 1 -name "*.uproject" | head -1

If no .uproject found → STOP.

"This skill requires an Unreal Engine project (a .uproject file must be in the working directory). The current directory does not appear to be a UE project. Navigate to the project root and retry."

2. Task Is Debugging-Related Check

The task must involve debugging or investigating a runtime or compile-time issue in C++ or Blueprint code. If there is no debugging component → STOP and inform the user this skill only handles debugging.

3. Build Configuration Check — Required Before Setting C++ Breakpoints

Before placing any breakpoints in game module C++ code, verify the binary was compiled in DebugGame Editor (or Debug Editor). In Development Editor the compiler inlines and optimises away most function entry points — breakpoints silently fail with:

"The breakpoint will not currently be hit. No executable code is associated with this line."

How to check: After xdebug_set_breakpoint, inspect the response for breakpointErrorsTail entries containing that message. If present → STOP. Instruct the user to switch Rider's build configuration to DebugGame Editor and rebuild before continuing. Do not attempt to fire the repro until the breakpoint is confirmed bound.

Engine-only breakpoints (RiderLink, UE core) are unaffected — this check applies only to the project's own game modules.

4. Rider MCP Availability Check

Check the <system-reminder> deferred-tool list for Rider MCP tools. Load live schemas with ToolSearch before calling any tool. Schemas are authoritative for parameter names — never guess. If execute_tool is the only tool returned, use CLI mode (see reference/rider-mcp-tools.md — execute_tool mode).

If no Rider MCP tools appear in the deferred list:

"Rider MCP tools are unavailable. Open Rider with this project loaded and the MCP server enabled, then retry. Falling back to Bash/Grep — call hierarchy and IDE diagnostics will not run."

Proceed with Bash/Grep/Read only, skipping all mcp__<prefix>__* steps. Document that Rider intelligence steps were skipped.

Path Selection

Fast path for targeted fixes — known function, single file, clear root cause:

1. Verify .uproject (Gate 1)
2. Locate the function with search_symbol or rg
3. Read the file using the standard Read tool; confirm the bug
4. Apply fix with the standard Edit tool
5. Run get_file_problems if Rider MCP is available
6. Build and verify

Full workflow for crash investigation, unknown root cause, GC/threading bugs, or multi-file changes → continue to Checklist below.

Checklist

Use the agent's native planning/todo mechanism when available. For simple one-file tasks, keep the plan implicit and proceed directly. For complex investigations, track:

1. GATE — UE project check + task check + Rider prefix resolution
2. Triage — classify the entry point: crash dump, log error, or live repro
3. Locate — find the suspect symbol; read its definition and call hierarchy
4. Analyze — trace callers/callees; find IDE-detected problems on suspect files
5. Instrument — identify breakpoint locations; add targeted logging if needed
6. Reproduce — confirm the issue triggers at the identified location
7. Fix — apply the minimal correct fix using the standard Edit tool
8. Verify — build and confirm the issue no longer reproduces

Workflow

Search routing: use rg/Grep for portable text discovery; use Rider search_text/search_file when IDE index, generated/reflected UE code, or unsaved editor state helps. Use Rider semantic tools (search_symbol, analyze_calls, get_symbol_info, get_file_problems, build) for code intelligence. analyze_calls supports C++ (ReSharper backend) — if it returns "No call hierarchy provider found", fall back to Grep.

Step 0 — Triage: Classify the Entry Point

Crash Dump Analysis

Find crash artifacts in Saved/Crashes/ (editor) or the platform crash folder — see reference/crash-patterns.md for locations and minidump instructions.

Read the crash log first:

find Saved/Crashes -name "*.log" | sort -r | head -1 | xargs tail -100

Look for Fatal error, Assertion failed, Unhandled Exception, or call stack near the end.

Identify the crash signature from the callstack address pattern — see reference/crash-patterns.md — Quick Diagnosis Table.

Map the callstack to source: take the topmost non-engine frame and find it with search_symbol.

Continue from Step 1 using that symbol.

Live PIE Inspection

When PIE is running, use ue_execute_python to query live game state before reading source files — often resolves the question in one call.

Script must be a single line — no \n, no indented blocks. Use ; and comprehensions.
See reference/ue-python-inspection.md for ready-to-use query patterns and API pitfalls.

Typical first queries (adapt to project-specific classes):

• World + player valid: import unreal; w=unreal.get_editor_subsystem(unreal.UnrealEditorSubsystem).get_game_world(); pc=unreal.GameplayStatics.get_player_controller(w,0); print(w,pc)
• Pawn class: ...; p=pc.get_controlled_pawn(); print(p.get_class().get_name() if p else None)
• ASC on PlayerState: ...; asc=pc.player_state.get_component_by_class(unreal.AbilitySystemComponent); print(asc.get_name() if asc else None)
• Active gameplay tags: ...; print(list(asc.get_owned_gameplay_tags()))

After confirming runtime state, continue from Step 1 to locate the responsible source code.

Log Analysis

find Saved/Logs -name "*.log" | sort -r | head -1
grep -n "Fatal\|Error\|Assertion failed\|ensure(" Saved/Logs/<Project>.log | tail -50
grep -n "Warning" Saved/Logs/<Project>.log | grep -v "LogTemp\|LogSlate" | tail -30

See reference/crash-patterns.md — Log Patterns for common entries and root causes. Continue from Step 1.

Step 1 — Locate the Suspect Code

Use search_symbol to find the suspect class or function. Read the source files using the standard Read tool.

If starting from a crash address or log string rather than a known symbol, use search_text restricted to *.cpp.

Step 2 — Trace the Call Hierarchy

Use analyze_calls — it supports C++ via the ReSharper C++ backend.

If the tool returns "No call hierarchy provider found" (symbol not indexed), fall back to Grep to find callers. Read the function body directly to find callees.

See reference/ue-debug-patterns.md — Call Hierarchy Analysis for what to look for in results.

Step 3 — Get Symbol Info for Context

get_symbol_info is position-based — use the standard Read tool first to find the symbol's exact line and column.

Use to confirm API contracts — whether a function is editor-only, can return nullptr, or has threading guarantees. Do not rely on training-data assumptions for version-specific UE APIs.

Step 4 — Run IDE Diagnostics on Suspect Files

Run get_file_problems on all suspect files (.h and .cpp). For multiple files, use lint_files.

• Error — likely directly related to the bug; address first
• Warning — check if it matches the crash symptom
• Hint / Info — note for context; not blockers

Step 5 — Set Breakpoints and Launch the Debugger

Do not just tell the user where to set breakpoints — set them via MCP. Pick the last point of known-good state, not the crash site.

Load the required tools first (if not already loaded):

ToolSearch(query: "select:mcp__<prefix>__xdebug_set_breakpoint,mcp__<prefix>__xdebug_get_debugger_status,mcp__<prefix>__xdebug_get_frame_values,mcp__<prefix>__xdebug_get_stack,mcp__<prefix>__ue_play,mcp__<prefix>__ue_status,mcp__<prefix>__execute_run_configuration,mcp__<prefix>__get_run_configurations")

5a — Check editor and PIE state using ue_status.

• If not connected → launch the editor using get_run_configurations then execute_run_configuration.
• If connected and PIE idle → proceed to 5b.
• If PIE already running → proceed to 5b directly.

5b — Set breakpoints using xdebug_set_breakpoint. Set standard, conditional, or logpoint breakpoints as appropriate. See reference/ue-debug-patterns.md — Breakpoint Placement Strategies for placement rules.

5c — Start PIE using ue_play if not already running.

5d — Wait for breakpoint hit, then inspect using xdebug_get_debugger_status, xdebug_get_stack, xdebug_get_frame_values.

Step 6 — Add Targeted Instrumentation (if needed)

If a live debugger session is not feasible, add UE_LOG statements using the standard Edit tool.

See reference/ue-debug-patterns.md — Instrumentation Rules. After editing, run get_file_problems to confirm no new errors.

Step 7 — Fix

Apply the fix using the standard Edit tool.

After editing: run get_file_problems on the changed file (and .h if touched). Fix the root cause, not the symptom — see reference/ue-debug-patterns.md — Fix: Root Cause vs Symptom.

Step 8 — Build and Verify

Run build_solution_start and poll build_solution_state until complete.

After a successful build:

1. Reproduce the original issue — confirm it no longer occurs
2. Run get_project_problems on the changed module; address new warnings on your files
3. Remove any instrumentation logging added in Step 6
4. Use reformat_file on changed files

see: reference/rider-mcp-tools.md — ALL Rider MCP tools: complete parameter reference, execute_tool mode table, UE editor/asset/debugger tools see: reference/rider-debug-tools.md — Debugging workflow patterns: crash callstack, intermittent bugs, packaged build crashes, live PIE inspection, breakpoint sequences see: reference/ue-debug-patterns.md — UE debugging patterns: call hierarchy analysis, instrumentation rules, fix guidance, breakpoint placement, GC/threading patterns see: reference/crash-patterns.md — Crash patterns: address signatures, GC crashes, assertion failures, async loading, Slate null widgets, log patterns see: reference/ue-python-inspection.md — UE Python runtime inspection: single-line scripting rules, world/player/component access, GAS/stat-tag queries, GameplayTag API pitfalls, common errors