Integrating Google Gemini API in PHP (Generate Content & List Models)

We will learn how to connect our PHP project to Google Gemini using two practical scripts:

(1) Generate Content with our chosen model and prompt.
(2) List Models to discover the latest available Gemini models. Both scripts use cURL and a simple settings.php file to keep your API key separate.

Prerequisites

• Create a Google API key for Gemini and keep it ready.
• Add a settings.php with $GOOGLE_API_KEY defined.
• Ensure PHP cURL extension is enabled on your server.

1) Generate Content with a Gemini Model

Use this script to send a prompt to Gemini and print the response as HTML (safe for direct display). Update the $MODEL and $text as needed.

<?php
require 'settings.php'; // must define: $GOOGLE_API_KEY
$MODEL   = 'gemini-2.5-flash'; // <- update model
$text = " Write a short poem about the stars."; // Update your text

$url = "https://generativelanguage.googleapis.com/v1beta/models/$MODEL:generateContent";

$payload = [
  "contents" => [[
    "parts" => [["text" => $text]]
  ]]
];

$ch = curl_init($url);
curl_setopt_array($ch, [
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_POST => true,
  CURLOPT_HTTPHEADER => [
    'Content-Type: application/json',
    "x-goog-api-key: $GOOGLE_API_KEY",
  ],
  CURLOPT_POSTFIELDS => json_encode($payload),
]);
$res = curl_exec($ch);
if (curl_errno($ch)) {
  die('cURL error: ' . curl_error($ch));
}
curl_close($ch);

$data = json_decode($res, true);
if (isset($data['candidates'][0]['content']['parts'][0]['text'])) {
  echo nl2br(htmlspecialchars($data['candidates'][0]['content']['parts'][0]['text']));
} else {
  // Show full response for debugging
  echo '<pre>'.print_r($data, true).'</pre>';
}
?>

Notes

• Model choice: gemini-2.5-flash is fast and good for short-form content. Switch to another model if needed.
• Safety: The output is HTML-escaped via htmlspecialchars() to prevent injection.
• Prompting: Keep your instructions explicit. You can also include URLs and formatting requirements.

2) List Available Gemini Models (with Pagination)

This helper lists all models from the ListModels endpoint. It handles pagination and prints a compact HTML table with name, display name/description, and supported generation methods.

<?php
// list-models.php
require 'settings.php'; // must define: $GOOGLE_API_KEY

/**
 * Fetch all models from Gemini ListModels endpoint (handles pagination).
 * @return array Decoded list of models (each item is an associative array)
 */
function fetchAllModels($apiKey) {
  $baseUrl = "https://generativelanguage.googleapis.com/v1beta/models";
  $models  = [];
  $pageTok = null;

  do {
    $url = $baseUrl . ($pageTok ? ("?pageToken=" . urlencode($pageTok)) : "");
    $ch = curl_init($url);
    curl_setopt_array($ch, [
      CURLOPT_RETURNTRANSFER => true,
      CURLOPT_HTTPHEADER => [
        "x-goog-api-key: $apiKey",
        "Accept: application/json"
      ],
      CURLOPT_TIMEOUT => 20,
    ]);
    $res = curl_exec($ch);
    if (curl_errno($ch)) {
      throw new RuntimeException('cURL error: ' . curl_error($ch));
    }
    curl_close($ch);

    $data = json_decode($res, true);
    if (isset($data['error'])) {
      throw new RuntimeException("API error: " . ($data['error']['message'] ?? 'unknown'));
    }

    foreach (($data['models'] ?? []) as $m) {
      $models[] = $m;
    }
    $pageTok = $data['nextPageToken'] ?? null;
  } while ($pageTok);

  return $models;
}

try {
  if (empty($GOOGLE_API_KEY)) {
    throw new RuntimeException("Missing GOOGLE_API_KEY in settings.php");
  }

  $models = fetchAllModels($GOOGLE_API_KEY);

  // Simple HTML table output (safe to embed in your admin/tools page)
  echo "<h3>Available Gemini Models</h3>";
  echo "<table border='1' cellpadding='6' cellspacing='0'>";
  echo "<tr><th>Name</th><th>Description</th><th>Generation Methods</th></tr>";

  foreach ($models as $m) {
    $name   = htmlspecialchars($m['name'] ?? '');
    $desc   = htmlspecialchars($m['displayName'] ?? ($m['description'] ?? ''));
    $meth   = htmlspecialchars(implode(', ', $m['supportedGenerationMethods'] ?? []));
    echo "<tr><td><code>{$name}</code></td><td>{$desc}</td><td>{$meth}</td></tr>";
  }
  echo "</table>";

  // Optional: quick JSON dump for debugging
  // echo "<pre>" . htmlspecialchars(json_encode($models, JSON_PRETTY_PRINT)) . "</pre>";

} catch (Throwable $e) {
  http_response_code(500);
  echo "<pre>Error: " . htmlspecialchars($e->getMessage()) . "</pre>";
}
?>

settings.php (Example)

Keep your API key outside version control (use environment variables or server configs). A simple starter:

<?php
// settings.php
$GOOGLE_API_KEY = getenv('GOOGLE_API_KEY') ?: 'YOUR_API_KEY_HERE';
?>

Troubleshooting

• 401/403: Check API key, quotas, and whether the Gemini API is enabled for your project.
• Timeouts: Increase CURLOPT_TIMEOUT for long responses.
• Empty content: Print the raw response (already included) to see error details from the API.
• Model not found: Run list-models to verify the exact model name and supported generation methods.

Subhendu Mohapatra

Author

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