AWS Bedrock Tutorial — Build Image Alt Text Generator in NodeJS

Randomness and diversity

Temperature: Randomness (Creative responses) Top P: Most probable answer

Reducing these number decreases hallucination (fluff).

Response Length

Maximum number of characters (tokens) you want the AI to reply in.

Here are the steps to get started

1. Create JavaScript or TypeScript file i.e. index.js, index.ts
2. Import BedrockRuntimeClient and InvokeModelCommand from aws-sdk
3. Initialise bedrock runtime client
4. Create model input with the prompt (body)
5. Create InvokeModelCommand by passing stringified body and model id
6. Use bedrock client to send the command
7. Convert buffer into string
8. Parse JSON from the string

JavaScript Code

This code encodes the input prompt and decodes the output from AI (Nova Bedrock) and then logs everything in the CLI.

import {
  BedrockRuntimeClient,
  InvokeModelCommand,
} from "@aws-sdk/client-bedrock-runtime";

const brockClient = new BedrockRuntimeClient({});

const prompt = "How old is earth? just tell the number & unit";

const modelInput = {
  messages: [
    {
      role: "user",
      content: [
        {
          text: prompt,
        },
      ],
    },
  ],
};

const modelCmd = new InvokeModelCommand({
  modelId: "amazon.nova-lite-v1:0",
  body: JSON.stringify(modelInput),
});

const res = await brockClient.send(modelCmd);
// Convert Bedrock response buffer to string
const jsonRes = Buffer.from(res.body).toString("utf8");

console.dir(JSON.parse(jsonRes), { depth: null });

Run your script with node or tsx:

node index.js

Response output format

You will see your answer inside messages in content array object.

{
  output: {
    message: {
		content: [ {
			text: '4.54 billion years' // <-the answer
		} ],
	    role: 'assistant'
	}
  },
  stopReason: 'end_turn',
  usage: { inputTokens: 12, outputTokens: 7, totalTokens: 19 }
}

We also get to know:

• How many tokens were used
• What was the reason to stop

Image analysis output

Now when we run the program again we see the output:

Two dogs dressed in ghost costumes are standing next to each other.

Now you know how to use Amazon Bedrock! Happy hacking :)