Promptopia MCP

Instructions

Implementation Reference

• src/services/prompts.service.ts:270-318 (handler)

  Core handler function that implements the apply_prompt tool logic: validates input, loads prompt, checks and replaces variables in single-content or multi-message prompts, returns formatted result.

  async applyPrompt(params: ApplyPromptParams): Promise<ApplyPromptResult> {
    if (!params.id || !params.id.trim()) {
      throw new ValidationError('Prompt ID is required')
    }
  
    if (!params.variables || typeof params.variables !== 'object') {
      throw new ValidationError('Variables must be provided as an object')
    }
  
    try {
      const prompt = await this.getPrompt(params.id)
      
      // Check if all required variables are provided
      const missingVariables = prompt.variables.filter(
        variable => !(variable in params.variables)
      )
      
      if (missingVariables.length > 0) {
        throw new ValidationError(
          `Missing required variables: ${missingVariables.join(', ')}`
        )
      }
      
      if (isMultiMessagePrompt(prompt)) {
        // Handle multi-message prompts
        const appliedMessages = prompt.messages.map(message => ({
          ...message,
          content: {
            ...message.content,
            ...(message.content.type === 'text' && message.content.text && {
              text: this.replaceVariables(message.content.text, params.variables)
            })
          }
        }))
  
        return {
          result: JSON.stringify(appliedMessages, null, 2),
          messages: appliedMessages
        }
      } else {
        // Handle single content prompts
        const result = this.replaceVariables(prompt.content, params.variables)
        return { result }
      }
    } catch (error) {
      console.error('Failed to apply prompt:', error)
      throw error
    }
  }

• src/handlers/tools.handler.ts:260-271 (handler)

  MCP tool dispatch handler for 'apply_prompt': extracts args, calls PromptsService.applyPrompt, formats response as MCP content.

  case 'apply_prompt': {
    const { id, variables } = args
    const result = await this.promptsService.applyPrompt({ id, variables })
    return {
      content: [{
        type: 'text',
        text: typeof result.result === 'string'
          ? result.result
          : JSON.stringify(result, null, 2)
      }]
    }
  }

• src/handlers/tools.handler.ts:130-146 (registration)

  Tool registration in listTools(): defines name, description, and inputSchema for 'apply_prompt'.

    name: 'apply_prompt',
    description: 'Applies variables to a template prompt and returns the result',
    inputSchema: {
      type: 'object',
      properties: {
        id: {
          type: 'string',
          description: 'ID of the prompt to apply'
        },
        variables: {
          type: 'object',
          description: 'Object containing variable names and their values'
        }
      },
      required: ['id', 'variables']
    }
  },

• src/types/index.ts:69-77 (schema)

  Type definitions for ApplyPromptParams (input) and ApplyPromptResult (output) used by the tool.

  export interface ApplyPromptParams {
    id: string
    variables: Record<string, string>
  }
  
  export interface ApplyPromptResult {
    result: string
    messages?: PromptMessage[] // For multi-message prompts
  }