Anthropic Request Builder
Build and preview Anthropic Claude API requests with code generation
Configuration
{
"model": "claude-sonnet-4-20250514",
"max_tokens": 1024,
"system": "You are a helpful AI assistant.",
"messages": [
{
"role": "user",
"content": "Hello! How can you help me today?"
}
]
}Key Differences from OpenAI
- • System prompt is a top-level parameter, not in messages array
- • Uses
max_tokens(required) notmax_completion_tokens - • Temperature range: 0-1 (not 0-2)
- • Has
top_kin addition totop_p
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Anthropic Messages API: Complete Request Builder Guide
The Anthropic Messages API is the interface for accessing Claude models — Claude 3.5 Sonnet, Claude 3 Opus, Claude 3.5 Haiku, and the latest Claude Sonnet 4. This request builder helps you configure API calls visually and generates ready-to-use code.
Claude models are known for strong instruction following, nuanced reasoning, and long context windows (up to 200K tokens). Use this tool to experiment with parameters and generate production-ready code.
Key API Differences vs OpenAI
| Feature | Anthropic | OpenAI |
|---|---|---|
| System prompt | Top-level system field | In messages array |
| Max tokens | Required | Optional |
| Temperature range | 0 to 1 | 0 to 2 |
| Top K sampling | Supported | Not available |
| Auth header | x-api-key | Authorization: Bearer |
Frequently Asked Questions
Which Claude model should I use?
Claude Sonnet 4 is the balanced choice for most tasks. Use Opus 4 for the most complex reasoning and creative tasks. Use Haiku 3.5 for fast, simple tasks at lower cost.
What is Top K sampling?
Top K limits token selection to the K most likely tokens. Unlike Top P which is probability-based, Top K is count-based. Use it for more predictable output variety. Set to 0 to disable.
Why is max_tokens required?
Anthropic requires explicit max_tokens to prevent unexpected costs from very long responses. Set it based on expected response length. Default is typically 1024 for chat, higher for longer content generation.