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perfonext-render-mcp

perfonext-render-mcp

by souvikdu
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
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Get Captured Renders

get_captured_renders

Check live render-capture progress without stopping the session to diagnose issues. Returns commit count, components seen, and instrumentation health signals for Next.js performance analysis.

Instructions

Optional diagnostic: peek at the live progress of a render-capture session without stopping it. Returns commit count, components seen, whether actualDuration is populating, and an unknownEvents count (non-zero = instrumentation may not be wired correctly). Only call this if something seems wrong — it is not a required step before stop_render_capture.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "sessionId": "<sessionId>"
    },
    "name": "get_captured_renders"
  }
}

Input Schema

NameRequiredDescriptionDefault
sessionIdYesThe sessionId returned by begin_render_analysis

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.5.2

TDQS

A4.7/5.0
Behavior5/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure and does so well. It explains that the tool does not stop the session, what fields it returns, and how to interpret an important signal (unknownEvents count). This is strong transparency for a diagnostic tool.

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 well-structured, opening with the key diagnostic purpose and then providing concrete return-value context. Every sentence contributes useful information—purpose, behavior, return fields, and usage guidance—without fluff.

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

Completeness5/5

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

For a simple one-parameter diagnostic tool, the description covers what the tool does, when to call it, what it returns, and how to interpret a non-obvious result. The absence of an output schema is adequately compensated by the explicit list of returned information.

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%, and the schema already documents sessionId as returned by begin_render_analysis. The description does not need to add parameter meaning, so the baseline 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 clearly identifies the tool as a diagnostic for peeking at live render-capture session progress, naming the specific resource and the non-destructive nature of the operation. It distinguishes itself from the sibling tools like stop_render_capture by explicitly stating it is not a required step before stopping.

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

Usage Guidelines5/5

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

The description explicitly states when to use this tool ('Only call this if something seems wrong') and what it is not for ('not a required step before stop_render_capture'). This gives clear usage context and prevents unnecessary invocation.

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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