INVALID_PROMPT_INPUT

A prompt template received missing or invalid input variables.

One unexpected way this can occur is if you add a JSON object directly into a prompt template:

import { PromptTemplate } from "@langchain/core/prompts";
import { ChatOpenAI } from "@langchain/openai";

const prompt = PromptTemplate.fromTemplate(`You are a helpful assistant.

Here is an example of how you should respond:

{
  "firstName": "John",
  "lastName": "Doe",
  "age": 21
}

Now, answer the following question:

{question}`);

You might think that the above prompt template should require a single input key named question, but the JSON object will be interpreted as an additional variable because the curly braces ({) are not escaped, and should be preceded by a second brace instead, like this:

import { PromptTemplate } from "@langchain/core/prompts";
import { ChatOpenAI } from "@langchain/openai";

const prompt = PromptTemplate.fromTemplate(`You are a helpful assistant.

Here is an example of how you should respond:

{{
  "firstName": "John",
  "lastName": "Doe",
  "age": 21
}}

Now, answer the following question:

{question}`);

Troubleshooting

The following may help resolve this error:

• Double-check your prompt template to ensure that it is correct.
  • If you are using default formatting and you are using curly braces { anywhere in your template, they should be double escaped like this: {{, as shown above.
• If you are using a MessagesPlaceholder, make sure that you are passing in an array of messages or message-like objects.
  • If you are using shorthand tuples to declare your prompt template, make sure that the variable name is wrapped in curly braces (["placeholder", "{messages}"]).
• Try viewing the inputs into your prompt template using LangSmith or log statements to confirm they appear as expected.
• If you are pulling a prompt from the LangChain Prompt Hub, try pulling and logging it or running it in isolation with a sample input to confirm that it is what you expect.