mcp-msgdump

replay_session

Replay recorded MCP message logs from a JSONL file, with optional filtering by method and custom start index, to reproduce and analyze past sessions.

Instructions

Replay a log file of MCP messages, optionally filtered by tool name.

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": {
      "path": "<path>"
    },
    "name": "replay_session"
  }
}

Input Schema

Name	Required	Description
`path`	Yes	Path to the JSONL log file to replay.
`filter_tool`	No	Only replay messages whose method contains this string.
`start_index`	No	Zero-based index to start replaying from. Default 0.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 8, 2026

TDQS

A3.5/5.0

Behavior2/5

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

No annotations are provided, so the description carries the full burden of disclosing side effects. 'Replay' strongly implies that MCP messages will be executed or sent, which could cause side effects, but the description does not state this or any safety implications.

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 a single, concise sentence with no redundant or vague wording. It efficiently communicates the core purpose and the optional filtering capability.

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

Completeness3/5

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

The description covers the basic purpose and parameters, but it omits important context such as what happens when messages are replayed, whether the operation is safe, and what output or result is expected. Given no annotations or output schema, these gaps leave the description only partially complete.

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 each parameter has a corresponding description. However, the descriptions add little beyond the schema itself—for example, 'filter_tool' is described only as a string filter and 'start_index' as a zero-based index, with no additional semantics or constraints.

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 states the specific action ('Replay a log file of MCP messages') and the optional filtering constraint ('filtered by tool name'). This distinguishes it from the sibling tool 'analyze_log', which implies analysis rather than replay.

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

Usage Guidelines3/5

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

The description implies when to use the tool—when replaying a log—but does not explicitly state when to prefer it over alternatives like 'analyze_log' or when not to use it. The usage guidance is implicit rather than explicit.

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

Deploy Server