/memory-leak-debugging

name: memory-leak-debugging
description: Diagnoses and resolves memory leaks in JavaScript/Node.js applications. Use when a user reports high memory usage, OOM errors, or wants to capture, compare, or inspect heap snapshots with Chrome DevTools MCP memory tools.

Memory Leak Debugging

This skill provides expert guidance and workflows for finding, diagnosing, and fixing memory leaks in JavaScript and Node.js applications using Chrome DevTools MCP tools.

Core Principles

• **Prefer MCP memory tools:** Do NOT attempt to read raw `.heapsnapshot` files directly, as they are extremely large and will consume too many tokens. Use the Chrome DevTools MCP heap snapshot tools to summarize, compare, and inspect snapshots.
• **Isolate the Leak:** Determine if the leak is in the browser (client-side) or Node.js (server-side).
• **Common Culprits:** Look for detached DOM nodes, unhandled closures, global variables, event listeners not being removed, and caches growing unbounded. _Note: Detached DOM nodes are sometimes intentional caches; always ask the user before nulling them._
• **Close Loaded Snapshots:** Heap snapshots can be large. After completing an investigation, use `close_heapsnapshot` for each loaded snapshot to release memory held by the MCP server.

Workflows

1. Capturing Snapshots

When investigating a frontend web application memory leak, utilize the `chrome-devtools-mcp` tools to interact with the application and take snapshots.

• Use tools like `click`, `navigate_page`, `fill`, etc., to manipulate the page into the desired state.
• Revert the page back to the original state after interactions to see if memory is released.
• Repeat the same user interactions 10 times to amplify the leak.
• Use `take_heapsnapshot` to save `.heapsnapshot` files to disk at baseline, target (after actions), and final (after reverting actions) states.

2. Comparing Snapshots

Once you have generated `.heapsnapshot` files using `take_heapsnapshot`, compare them with Chrome DevTools MCP memory tools.

• Start with `get_heapsnapshot_summary` for each snapshot to confirm that the files load and to compare high-level totals.
• Use `compare_heapsnapshots` to compare baseline and target snapshots. Start without `classIndex` for the summary diff, then request detailed class diffs only for suspicious growth by specifying `classIndex`.
• Use the summary output from `compare_heapsnapshots` before drilling into specific node IDs.

3. Inspecting Retainers and Dominator Chains

When a class or object type grows unexpectedly, inspect the retaining chain and dominators with the MCP tools before changing code.

• Use `get_heapsnapshot_class_nodes` to list instances of the suspicious class.
• Use `get_heapsnapshot_retainers`, `get_heapsnapshot_retaining_paths`, `get_heapsnapshot_dominators`, and `get_heapsnapshot_edges` to understand why representative nodes are still reachable.
• Use `get_heapsnapshot_object_details` with a specific `nodeId` to retrieve detailed object metadata (size, type, distance, and DOM detachedness).
• Use `get_heapsnapshot_duplicate_strings` when string growth dominates the diff.
• Read [references/common-leaks.md](references/common-leaks.md) for examples of common memory leaks and how to fix them after the retaining path points at application code.

4. Advanced Analysis and Categorized Filters

Use built-in MCP memory tools and filters to pinpoint specific leak categories directly without external tools.

• Use `get_heapsnapshot_details` or `get_heapsnapshot_class_nodes` with `filterName` to target common leak causes:
• `objectsRetainedByDetachedDomNodes`: Identifies detached DOM elements retained in memory.
• `objectsRetainedByEventHandlers`: Identifies objects kept alive by unremoved event listeners.
• `objectsRetainedByContexts`: Identifies objects trapped in closures or execution contexts.
• `objectsRetainedByConsole`: Identifies objects retained by console logging.