Janus MCP

initialize_session

Start a session with an OpenAPI specification from a file or URL to enable AI-driven API exploration and integration.

Instructions

Initialize a new session with an OpenAPI specification file or URL

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": {
      "source": "<source>"
    },
    "name": "initialize_session"
  }
}

Input Schema

Name	Required	Description	Default
`source`	Yes	Path to the OpenAPI JSON or YAML file, or URL to fetch the specification from
`outputFormat`	No	Output format for responses (default: compact). Can be changed later with set_output_format.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.1.1Sep 13, 2026

TDQS

C2.9/5.0

Behavior2/5

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

With no annotations and no output schema, the description carries full behavioral disclosure burden. It doesn't state whether session initialization has side effects, whether it validates the spec, what happens on failure, or whether the session must be removed later. Only the core action is stated.

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

Conciseness4/5

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

A single, efficient sentence with the key action and resource front-loaded. No filler, though it could benefit from a usage hint without losing conciseness.

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?

For a session-initialization tool with no annotations and no output schema, the description should clarify lifecycle expectations (e.g., must call remove_session), permissions, or return behavior. It omits all of this.

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 documents both parameters in detail. The description adds no parameter-level meaning beyond restating the accepted input type. Baseline 3 is appropriate when the schema does the heavy lifting.

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

Purpose4/5

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

Clear verb+resource ('Initialize a new session') with the required input (OpenAPI spec file or URL). It doesn't distinguish itself from siblings like get_session_info or set_output_format, but the resource is specific enough for an agent to identify the tool's purpose.

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

Usage Guidelines2/5

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

No guidance on when to use this tool, prerequisites, or alternatives is provided. The description states what it does but not when it should be selected over other sibling tools.

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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