linshenkx/prompt-optimizer · error · Error

Prompt must not exceed 50,000 characters

Error message

Prompt must not exceed 50,000 characters

What it means

ParameterAdapter.validatePrompt throws this when prompt.length exceeds 50,000 characters. It is a hard limit on the prompt input to the MCP server, applied after the non-empty check and before any processing.

Source

Thrown at packages/mcp-server/src/adapters/parameter-adapter.ts:16

/**
 * 参数验证工具
 * 简化的参数验证，移除过度抽象
 */

export class ParameterValidator {

  /**
   * 验证提示词输入
   */
  static validatePrompt(prompt: string): void {
    if (!prompt || typeof prompt !== 'string' || prompt.trim().length === 0) {
      throw new Error('Prompt must be a non-empty string');
    }
    if (prompt.length > 50000) {
      throw new Error('Prompt must not exceed 50,000 characters');
    }
  }

  /**
   * 验证模板输入
   */
  static validateTemplate(template?: string): void {
    if (template !== undefined && (typeof template !== 'string' || template.trim().length === 0)) {
      throw new Error('Template must be a non-empty string');
    }
  }

  /**
   * 验证需求描述输入
   */
  static validateRequirements(requirements: string): void {
    if (!requirements || typeof requirements !== 'string' || requirements.trim().length === 0) {
      throw new Error('Requirements must be a non-empty string');

View on GitHub (pinned to 3e677b1d9f)

Solutions

1. Truncate or chunk the prompt before sending (keep under 50k chars)
2. Move large reference content into a dedicated document/context parameter if the tool provides one
3. Summarize long input with a cheap pre-pass before the main call

Example fix

// before
await tool.call({ prompt: entireFile });

// after
const MAX = 50000;
await tool.call({ prompt: entireFile.slice(0, MAX) });

const MAX_PROMPT = 50000;
if (prompt.length > MAX_PROMPT) prompt = prompt.slice(0, MAX_PROMPT);

const isWithinPromptLimit = (p: string): boolean => p.length <= 50000;

try { await call({ prompt }); } catch (e) { if ((e as Error).message.includes('50,000')) { prompt = prompt.slice(0, 50000); await call({ prompt }); } else throw e; }

When it happens

Trigger: Calling the MCP prompt endpoint with a prompt longer than 50,000 characters — e.g. pasting an entire file, concatenating many documents, or stuffing conversation history into the prompt field.

Common situations: RAG-style integrations inlining large documents into the prompt instead of a separate context parameter; prompt templates that loop-append content; logs/dumps accidentally concatenated into the prompt.

Related errors

• Prompt must be a non-empty string
• Requirements must not exceed 10,000 characters
• Iteration requirement must not be empty.
• ${label} promptText must not be empty.
• User prompt is required

AI-assisted analysis of linshenkx/prompt-optimizer@3e677b1d9f (2026-08-27). Data as JSON: /api/errors/638ebc2b794f957e. Report an issue: GitHub.