Mintplex-Labs/anything-llm · error · Error

Key must be less than 255 characters

Error message

Key must be less than 255 characters

What it means

Thrown by SystemPromptVariables._checkVariableKey when key.length > 255. Enforces the storage column width for the system_prompt_variables.key field. Runs on both create and update because _checkVariableKey is invoked before either prisma write.

Source

Thrown at server/models/systemPromptVariables.js:362

    } catch (error) {
      console.error("Error in expandSystemPromptVariables:", error);
      return str;
    }
  },

  /**
   * Internal function to check if a variable key is valid
   * @param {string} key
   * @param {boolean} checkExisting
   * @returns {Promise<boolean>}
   */
  _checkVariableKey: async function (key = null, checkExisting = true) {
    if (!key) throw new Error("Key is required");
    if (typeof key !== "string") throw new Error("Key must be a string");
    if (!/^[a-zA-Z0-9_]+$/.test(key))
      throw new Error("Key must contain only letters, numbers and underscores");
    if (key.length > 255)
      throw new Error("Key must be less than 255 characters");
    if (key.length < 3) throw new Error("Key must be at least 3 characters");
    if (key.startsWith("user."))
      throw new Error("Key cannot start with 'user.'");
    if (key.startsWith("system."))
      throw new Error("Key cannot start with 'system.'");
    if (checkExisting && (await this.get(key)) !== null)
      throw new Error("System prompt variable with this key already exists");

    return true;
  },
};

module.exports = { SystemPromptVariables };

View on GitHub (pinned to 526360e320)

Solutions

1. Shorten the key to 255 characters or fewer.
2. If a long source identifier is unavoidable, hash or abbreviate it before using as the key.
3. Enforce a max-length check in the submitting form.

Example fix

// before
SystemPromptVariables.create({ key: veryLongGeneratedString, value: '...' });
// after
const key = generatedString.slice(0, 255);
SystemPromptVariables.create({ key, value: '...' });

const MAX_KEY = 255;
if (typeof key === 'string' && key.length > MAX_KEY) {
  key = key.slice(0, MAX_KEY);
}

const isWithinKeyLimit = (k) => typeof k === 'string' && k.length <= 255;

When it happens

Trigger: POST/PUT /system/prompt-variables with a key string longer than 255 characters after it passes the character-class regex.

Common situations: Programmatically generated keys (hashed names, concatenated identifiers) exceeding the limit. Pasting a long identifier from another system without truncation.

Related errors

• Key is required
• Key must contain only letters, numbers and underscores
• Key cannot start with 'user.'
• Key cannot start with 'system.'
• System prompt variable with this key already exists

AI-assisted analysis of Mintplex-Labs/anything-llm@526360e320 (2026-08-13). Data as JSON: /api/errors/bb0298d0dd9e511f. Report an issue: GitHub.