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sawa-zen

VRChat MCP Server

vrchat_get_instance

Retrieve information about a specific VRChat instance by providing world and instance IDs. Access details like member data when authorized as the instance owner.

Instructions

Get information about a specific instance. Note: Detailed information about instance members is only available if you are the instance owner.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
worldIdYesMust be a valid world ID.
instanceIdYesMust be a valid instance ID.

Implementation Reference

  • The handler function that authenticates the VRChat client, retrieves the instance data using the instances API, and returns the JSON-formatted instance information or an error message.
    async (params) => {
      try {
        await vrchatClient.auth()
        const instance = await vrchatClient.instancesApi.getInstance(params.worldId, params.instanceId)
        return {
          content: [{
            type: 'text',
            text: JSON.stringify(instance.data, null, 2)
          }]
        }
      } catch (error) {
        return {
          content: [{
            type: 'text',
            text: 'Failed to get instance: ' + error
          }]
        }
      }
    }
  • Input schema defining the required parameters 'worldId' and 'instanceId' using Zod validation.
    {
      worldId: z.string().describe('Must be a valid world ID.'),
      instanceId: z.string().describe('Must be a valid instance ID.'),
    },
  • Registers the 'vrchat_get_instance' tool on the MCP server with name, description, input schema, and handler function.
      // Name
      'vrchat_get_instance',
      // Description
      'Get information about a specific instance. Note: Detailed information about instance members is only available if you are the instance owner.',
      {
        worldId: z.string().describe('Must be a valid world ID.'),
        instanceId: z.string().describe('Must be a valid instance ID.'),
      },
      async (params) => {
        try {
          await vrchatClient.auth()
          const instance = await vrchatClient.instancesApi.getInstance(params.worldId, params.instanceId)
          return {
            content: [{
              type: 'text',
              text: JSON.stringify(instance.data, null, 2)
            }]
          }
        } catch (error) {
          return {
            content: [{
              type: 'text',
              text: 'Failed to get instance: ' + error
            }]
          }
        }
      }
    )
  • src/main.ts:33-33 (registration)
    Calls createInstancesTools to register the vrchat_get_instance tool (among others) on the main MCP server instance.
    createInstancesTools(server, vrchatClient)
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 adds valuable context about the limitation on detailed member information based on ownership, which is a behavioral trait not covered by the input schema. However, it doesn't disclose other potential behaviors like error conditions, rate limits, authentication needs, or response format, leaving gaps for a tool with no annotations.

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 appropriately sized with two sentences: the first states the purpose clearly, and the second adds crucial context about ownership limitations. Every sentence earns its place by providing essential information without redundancy, making it front-loaded and efficient.

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?

Given the complexity of retrieving instance information with no annotations and no output schema, the description is partially complete. It covers the purpose and a key behavioral constraint (ownership-based access to details), but lacks information on return values, error handling, or other operational aspects. This leaves some gaps for effective tool use by an AI agent.

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?

The input schema has 100% description coverage, with clear documentation for 'worldId' and 'instanceId' as valid IDs. The description doesn't add any meaning beyond this, such as explaining what constitutes a valid ID or how to obtain these values. Given the high schema coverage, a baseline score of 3 is appropriate as the schema handles parameter semantics adequately.

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?

The description clearly states the tool's purpose as 'Get information about a specific instance,' which is a specific verb+resource combination. However, it doesn't explicitly differentiate from sibling tools like 'vrchat_get_current_user' or 'vrchat_search_worlds' that might also retrieve information, though the focus on 'instance' is distinct.

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 provides implied usage guidance through the note about detailed member information being available only to instance owners, which hints at when this tool is most useful. However, it doesn't explicitly state when to use this tool versus alternatives like 'vrchat_search_worlds' or 'vrchat_list_favorites,' nor does it mention prerequisites or exclusions beyond the ownership note.

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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