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react-profiler-renders

Scan the live React app's fiber tree to identify top re-rendering components, returning render counts and durations as a markdown table without a profiling session.

Instructions

Scan the live React fiber tree to collect component render counts and durations. Returns a markdown table of the top re-rendering components. No profiling session required — works on a live connected app. Use when you want a quick snapshot of render counts without a full profiling session. Fails if the React DevTools hook is not present in the runtime or the app is not connected.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
portNoMetro server port. Optional — omit it to use this device's port, 8081 by default. Ignored for Chromium, whose CDP port is encoded in device_id.
top_nNoNumber of top re-rendering components to return (default 20)
device_idYesDevice logicalDeviceId from debugger-connect (iOS simulator UDID or Android logicalDeviceId).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv0.25.0
    • removedInput schema / properties / port / default
      Removed value: -8081
    • changedInput schema / properties / port / description
      Previous value: -"Metro server port"New value: +"Metro server port. Optional — omit it to use this device's port, 8081 by default. Ignored for Chromium, whose CDP port is encoded in device_id."
    • addedInput schema / properties / port / maximum
      Added value: +65535
    • addedInput schema / properties / port / minimum
      Added value: +1
    • changedInput schema / properties / port / type
      Previous value: -"number"New value: +"integer"
  2. First observedv0.15.0

TDQS

A4.2/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full behavioral burden. It says no profiling session is required, the app must be connected, the live fiber tree is scanned, and it will fail if the React DevTools hook is missing. That goes beyond the minimal but leaves some side-effect semantics implicit rather than explicitly stating this is a read-only operation.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is four sentences with no filler. The main outcome is front-loaded, the key distinction from full profiling is stated clearly, and the failure conditions are given without redundant detail.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given no output schema and no annotations, the description covers operation, output shape, use case, and failure conditions well. It could be slightly stronger by explicitly naming a few sibling profiler tools, but the live-snapshot contrast with full profiling gives enough context for correct selection.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already fully documents device_id, port, and top_n. The description adds general context about 'top re-rendering components' but does not explain parameter formats or parameter-specific behavior beyond what the schema already states, so the baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific action and resource: scanning the live React fiber tree for render counts and durations. It returns a markdown table, and it explicitly distinguishes itself from a full profiling session, which differentiates it from sibling profiler tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It clearly states the intended use case: 'quick snapshot of render counts without a full profiling session.' However, it does not explicitly name alternative sibling tools like react-profiler-analyze or react-profiler-fiber-tree, so it stops short of giving full when-not and alternative guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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