> ## Documentation Index > Fetch the complete documentation index at: https://docs.cairhealth.com/llms.txt > Use this file to discover all available pages before exploring further. # Generate Letter of Medical Necessity > Generates a Letter of Medical Necessity (LMN) from uploaded procedure notes using AI analysis. The letter can be returned as plain text or as a formatted PDF document based on the `output_format` parameter. ## Overview This endpoint generates a Letter of Medical Necessity (LMN) from uploaded procedure notes using AI analysis. The letter can be returned in two formats: * **Text format** (default): Returns the letter content as plain text markdown * **PDF format**: Returns a professionally formatted PDF document with proper letter layout, including header, patient information, body content, signature, and footer ## Output Formats ### Text Format (`output_format: "text"` or omitted) When requesting text format, the response includes a `letter` field containing the markdown-formatted letter content. ### PDF Format (`output_format: "pdf"`) When requesting PDF format, the response includes a `fileContent` field containing a base64-encoded PDF document. The PDF includes: * Professional letter header with center name, contact information, and date * Patient information section * Formatted letter body with proper text wrapping * Signature section with expert name * Footer with generation timestamp ## OpenAPI ````yaml POST /api/generate-letter openapi: 3.1.0 info: title: Cair Health APIs description: APIs for the Cair Health platform license: name: MIT version: 1.0.0 servers: - url: https://forecaster.cairhealth.com security: - bearerAuth: [] paths: /api/generate-letter: post: description: >- Generates a Letter of Medical Necessity (LMN) from uploaded procedure notes using AI analysis. The letter can be returned as plain text or as a formatted PDF document based on the `output_format` parameter. requestBody: description: >- Request body containing base64 encoded file content and additional metadata content: application/json: schema: $ref: '#/components/schemas/GenerateLetterRequest' example: file_content: patient_identifier: PAT-12345 patient_name: John Doe patient_age: '45' facility_name: Medical Center visit_cost: '500.00' provider_email: contact@medicalcenter.com provider_phone: +1-555-123-4567 provider_signature: Dr. Jane Smith provider_name: Dr. Jane Smith, MD output_format: pdf required: true responses: '200': description: Letter of Medical Necessity generated successfully content: application/json: schema: $ref: '#/components/schemas/LetterResponse' examples: text_response: summary: Text format response, returned as plain text markdown value: letter: timestamp: '2025-10-16T14:30:45Z' invoice_cost: '500.00' patient_identifier: PAT-12345 pdf_response: summary: PDF format response, returned as base64 encoded string value: fileContent: timestamp: '2025-10-16T14:30:45Z' invoice_cost: '500.00' patient_identifier: PAT-12345 '400': description: Invalid request or file processing error content: application/json: schema: $ref: '#/components/schemas/Error' example: error: No file content provided '401': description: Unauthorized access or invalid organization ID content: application/json: schema: $ref: '#/components/schemas/Error' example: error: Organization not found '500': description: Server error or letter generation failure content: application/json: schema: $ref: '#/components/schemas/Error' example: error: Failed to generate letter from encounter security: - bearerAuth: [] components: schemas: GenerateLetterRequest: type: object description: >- Request body for generating a Letter of Medical Necessity from encounter notes properties: file_content: type: string description: Base64 encoded content of the procedure notes file (PDF) patient_identifier: type: string description: Unique identifier for the patient patient_name: type: string description: Patient's full name patient_age: type: string description: Patient's age facility_name: type: string description: Name of the medical facility or center visit_cost: type: string description: Cost of the visit or procedure provider_email: type: string description: Provider's contact email address format: email provider_phone: type: string description: Provider's contact phone number example: +1-555-123-4567 provider_signature: type: string description: Signature line text for the letter provider_name: type: string description: Name and credentials of the provider signing the letter example: Dr. Jane Smith, MD output_format: type: string enum: - text - pdf description: Output format for the letter. Defaults to 'text' if not specified. default: text required: - file_content - patient_identifier - patient_name - patient_age - facility_name - visit_cost - provider_email - provider_phone - provider_signature - provider_name LetterResponse: type: object description: >- Response containing the generated Letter of Medical Necessity. The response format depends on the `output_format` parameter in the request. properties: letter: type: string description: >- The generated Letter of Medical Necessity content in text format. Present when `output_format` is 'text' or not specified. fileContent: type: string description: >- Base64 encoded PDF content of the generated letter. Present when `output_format` is 'pdf'. timestamp: type: string description: Timestamp when the letter was generated format: date-time invoice_cost: type: string description: The visit cost associated with the letter generation patient_identifier: type: string description: The patient identifier associated with the letter required: [] Error: type: object properties: message: type: string description: Error message securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: JWT ````