Claude API curl Example

Call the Claude API with curl. Complete 2026 examples: basic message, streaming, tool use, system prompt, and JSON extraction — no SDK required.

curl is the fastest way to verify your API key, test prompt changes, or debug requests without writing any application code.

Prerequisites

export ANTHROPIC_API_KEY="sk-ant-your-key-here"

Minimal request

curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 256,
    "messages": [{"role": "user", "content": "Hello, Claude!"}]
  }'

With system prompt

curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 512,
    "system": "You are a concise technical writer. Respond in bullet points.",
    "messages": [{"role": "user", "content": "What is prompt caching?"}]
  }'

Extract just the text with jq

curl -s https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{"model":"claude-sonnet-4-6","max_tokens":256,"messages":[{"role":"user","content":"What is 12*34?"}]}' \
  | jq -r '.content[0].text'

Streaming response (SSE)

curl --no-buffer https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 512,
    "stream": true,
    "messages": [{"role": "user", "content": "Count from 1 to 10 slowly."}]
  }' | grep "^data:" | jq -r 'select(.type=="content_block_delta") | .delta.text // empty' 2>/dev/null

JSON extraction (structured output)

curl -s https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 256,
    "system": "Return only valid JSON. No explanation.",
    "messages": [{
      "role": "user",
      "content": "Extract: name, price, category from: Blue Widget, $12.99, Hardware"
    }]
  }' | jq '.content[0].text | fromjson'

Tool use (function calling)

curl -s https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 256,
    "tools": [{
      "name": "get_weather",
      "description": "Get weather for a city",
      "input_schema": {
        "type": "object",
        "properties": {"city": {"type": "string"}},
        "required": ["city"]
      }
    }],
    "messages": [{"role": "user", "content": "What is the weather in London?"}]
  }' | jq '.content[] | select(.type=="tool_use")'

Check token usage

curl -s https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{"model":"claude-sonnet-4-6","max_tokens":256,"messages":[{"role":"user","content":"Hello"}]}' \
  | jq '{input_tokens: .usage.input_tokens, output_tokens: .usage.output_tokens, stop_reason: .stop_reason}'

API parameters reference

Use these curl snippets as quick smoke tests before wiring the SDK into your app. Estimate token costs at the Claude API Cost Calculator.

Frequently asked questions

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