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heizaheiza

Charles MCP Server

get_recording_snapshot

Load a saved recording snapshot for network traffic analysis without accessing live Charles Proxy sessions.

Instructions

Load a saved recording snapshot. This tool never reads the live Charles session.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
pathNo

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
pathNo
itemsYes
sourceYes
warningsNo
total_itemsYes

Implementation Reference

  • The implementation of the get_recording_snapshot tool, which uses the history_service to retrieve a snapshot result.
    async def get_recording_snapshot(
        ctx: ToolContext,
        path: Optional[str] = None,
    ) -> RecordingSnapshotResult:
        """Load a saved recording snapshot. This tool never reads the live Charles session."""
        deps = get_tool_dependencies(ctx)
        try:
            return await deps.history_service.get_snapshot_result(path)
        except Exception as exc:
            raise ValueError(str(exc)) from exc
Behavior3/5

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. It successfully clarifies the data source (saved snapshots vs. live), but fails to explicitly state safety properties (read-only status), side effects, or whether loading affects current session state.

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 consists of two efficient sentences with zero waste. The primary purpose is front-loaded in the first sentence, while the second sentence provides essential behavioral context.

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

Completeness2/5

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

While the tool has an output schema (covering return values) and a simple single-parameter structure, the complete lack of parameter documentation in both schema and description, combined with absent annotations, leaves critical usage information gaps.

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

Parameters1/5

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

The input schema has 0% description coverage, and the description fails to compensate by providing any semantics for the 'path' parameter. It does not explain what the path represents, acceptable formats, or the behavior when null (the default).

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 provides a specific verb ('Load') and resource ('saved recording snapshot'), clearly defining the tool's function. It explicitly distinguishes the tool from live-capture siblings by stating it 'never reads the live Charles session.'

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?

The description provides clear contextual guidance via the negative constraint 'never reads the live Charles session,' implicitly defining when not to use this tool (vs. live capture tools). However, it does not explicitly name alternative tools like 'read_live_capture' for that use case.

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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