Gemini API Cheatsheet 2026 — Free Tier Limits, Models, and Endpoints in One Place

curl https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash-preview:generateContent \
  -H "Content-Type: application/json" \
  -H "x-goog-api-key: YOUR_API_KEY" \
  -d '{
    "contents": [{"parts": [{"text": "Your prompt here"}]}]
  }'

{
  "system_instruction": {
    "parts": [{"text": "You are a helpful assistant."}]
  },
  "contents": [
    {"role": "user", "parts": [{"text": "Your prompt here"}]}
  ]
}

curl https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash-preview:streamGenerateContent \
  -H "Content-Type: application/json" \
  -H "x-goog-api-key: YOUR_API_KEY" \
  -d '{"contents": [{"parts": [{"text": "Tell me a story"}]}]}'

use reqwest::Client;
use serde_json::json;

pub async fn call_gemini(prompt: &str, api_key: &str) -> Result {
    let client = Client::new();
    let url = format!(
        "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash-preview:generateContent?key={}",
        api_key
    );

    let body = json!({
        "contents": [{"parts": [{"text": prompt}]}]
    });

    let res = client.post(&url).json(&body).send().await?;
    let data: serde_json::Value = res.json().await?;

    let text = data["candidates"][0]["content"]["parts"][0]["text"]
        .as_str()
        .unwrap_or("")
        .to_string();

    Ok(text)
}