Imported from kohebth/agent-skill-sets (.gemini/skills/moodle-external-api-development/SKILL.md). Install upstream with npx skills add kohebth/agent-skill-sets --skill moodle-external-api-development. Copyright stays with the author.

Moodle External API Development

This skill guides you through creating custom external web service APIs for Moodle LMS, following Moodle's external API framework and coding standards.

When to Use This Skill

• Creating custom web services for Moodle plugins
• Implementing REST/AJAX endpoints for course management
• Building APIs for quiz operations, user tracking, or reporting
• Exposing Moodle functionality to external applications
• Developing mobile app backends using Moodle

Core Architecture Pattern

Moodle external APIs follow a strict three-method pattern:

1. execute_parameters() - Defines input parameter structure
2. execute() - Contains business logic
3. execute_returns() - Defines return structure

Step-by-Step Implementation

Step 1: Create the External API Class File

Location: /local/yourplugin/classes/external/your_api_name.php

<?php
namespace local_yourplugin\external;

defined('MOODLE_INTERNAL') || die();
require_once("$CFG->libdir/externallib.php");

use external_api;
use external_function_parameters;
use external_single_structure;
use external_value;

class your_api_name extends external_api {
    
    // Three required methods will go here
    
}

Key Points:

• Class must extend external_api
• Namespace follows: local_pluginname\external or mod_modname\external
• Include the security check: defined('MOODLE_INTERNAL') || die();
• Require externallib.php for base classes

Step 2: Define Input Parameters

public static function execute_parameters() {
    return new external_function_parameters([
        'userid' => new external_value(PARAM_INT, 'User ID', VALUE_REQUIRED),
        'courseid' => new external_value(PARAM_INT, 'Course ID', VALUE_REQUIRED),
        'options' => new external_single_structure([
            'includedetails' => new external_value(PARAM_BOOL, 'Include details', VALUE_DEFAULT, false),
            'limit' => new external_value(PARAM_INT, 'Result limit', VALUE_DEFAULT, 10)
        ], 'Options', VALUE_OPTIONAL)
    ]);
}

Common Parameter Types:

• PARAM_INT - Integers
• PARAM_TEXT - Plain text (HTML stripped)
• PARAM_RAW - Raw text (no cleaning)
• PARAM_BOOL - Boolean values
• PARAM_FLOAT - Floating point numbers
• PARAM_ALPHANUMEXT - Alphanumeric with extended chars

Structures:

• external_value - Single value
• external_single_structure - Object with named fields
• external_multiple_structure - Array of items

Value Flags:

• VALUE_REQUIRED - Parameter must be provided
• VALUE_OPTIONAL - Parameter is optional
• VALUE_DEFAULT, defaultvalue - Optional with default

Step 3: Implement Business Logic

public static function execute($userid, $courseid, $options = []) {
    global $DB, $USER;

    // 1. Validate parameters
    $params = self::validate_parameters(self::execute_parameters(), [
        'userid' => $userid,
        'courseid' => $courseid,
        'options' => $options
    ]);

    // 2. Check permissions/capabilities
    $context = \context_course::instance($params['courseid']);
    self::validate_context($context);
    require_capability('moodle/course:view', $context);

    // 3. Verify user access
    if ($params['userid'] != $USER->id) {
        require_capability('moodle/course:viewhiddenactivities', $context);
    }

    // 4. Database operations
    $sql = "SELECT id, name, timecreated
            FROM {your_table}
            WHERE userid = :userid
              AND courseid = :courseid
            LIMIT :limit";
    
    $records = $DB->get_records_sql($sql, [
        'userid' => $params['userid'],
        'courseid' => $params['courseid'],
        'limit' => $params['options']['limit']
    ]);

    // 5. Process and return data
    $results = [];
    foreach ($records as $record) {
        $results[] = [
            'id' => $record->id,
            'name' => $record->name,
            'timestamp' => $record->timecreated
        ];
    }

    return [
        'items' => $results,
        'count' => count($results)
    ];
}

Critical Steps:

1. Always validate parameters using validate_parameters()
2. Check context using validate_context()
3. Verify capabilities using require_capability()
4. Use parameterized queries to prevent SQL injection
5. Return structured data matching return definition

Step 4: Define Return Structure

public static function execute_returns() {
    return new external_single_structure([
        'items' => new external_multiple_structure(
            new external_single_structure([
                'id' => new external_value(PARAM_INT, 'Item ID'),
                'name' => new external_value(PARAM_TEXT, 'Item name'),
                'timestamp' => new external_value(PARAM_INT, 'Creation time')
            ])
        ),
        'count' => new external_value(PARAM_INT, 'Total items')
    ]);
}

Return Structure Rules:

• Must match exactly what execute() returns
• Use appropriate parameter types
• Document each field with description
• Nested structures allowed

Step 5: Register the Service

Location: /local/yourplugin/db/services.php

<?php
defined('MOODLE_INTERNAL') || die();

$functions = [
    'local_yourplugin_your_api_name' => [
        'classname'   => 'local_yourplugin\external\your_api_name',
        'methodname'  => 'execute',
        'classpath'   => 'local/yourplugin/classes/external/your_api_name.php',
        'description' => 'Brief description of what this API does',
        'type'        => 'read',  // or 'write'
        'ajax'        => true,
        'capabilities'=> 'moodle/course:view', // comma-separated if multiple
        'services'    => [MOODLE_OFFICIAL_MOBILE_SERVICE] // Optional
    ],
];

$services = [
    'Your Plugin Web Service' => [
        'functions' => [
            'local_yourplugin_your_api_name'
        ],
        'restrictedusers' => 0,
        'enabled' => 1
    ]
];

Service Registration Keys:

• classname - Full namespaced class name
• methodname - Always 'execute'
• type - 'read' (SELECT) or 'write' (INSERT/UPDATE/DELETE)
• ajax - Set true for AJAX/REST access
• capabilities - Required Moodle capabilities
• services - Optional service bundles

Step 6: Implement Error Handling & Logging

private static function log_debug($message) {
    global $CFG;
    $logdir = $CFG->dataroot . '/local_yourplugin';
    if (!file_exists($logdir)) {
        mkdir($logdir, 0777, true);
    }
    $debuglog = $logdir . '/api_debug.log';
    $timestamp = date('Y-m-d H:i:s');
    file_put_contents($debuglog, "[$timestamp] $message\n", FILE_APPEND | LOCK_EX);
}

public static function execute($userid, $courseid) {
    global $DB;

    try {
        self::log_debug("API called: userid=$userid, courseid=$courseid");
        
        // Validate parameters
        $params = self::validate_parameters(self::execute_parameters(), [
            'userid' => $userid,
            'courseid' => $courseid
        ]);

        // Your logic here
        
        self::log_debug("API completed successfully");
        return $result;

    } catch (\invalid_parameter_exception $e) {
        self::log_debug("Parameter validation failed: " . $e->getMessage());
        throw $e;
    } catch (\moodle_exception $e) {
        self::log_debug("Moodle exception: " . $e->getMessage());
        throw $e;
    } catch (\Exception $e) {
        // Log detailed error info
        $lastsql = method_exists($DB, 'get_last_sql') ? $DB->get_last_sql() : '[N/A]';
        self::log_debug("Fatal error: " . $e->getMessage());
        self::log_debug("Last SQL: " . $lastsql);
        self::log_debug("Stack trace: " . $e->getTraceAsString());
        throw $e;
    }
}

Error Handling Best Practices:

• Wrap logic in try-catch blocks
• Log errors with timestamps and context
• Capture SQL queries on database errors
• Preserve stack traces for debugging
• Re-throw exceptions after logging

Advanced Patterns

Complex Database Operations

// Transaction example
$transaction = $DB->start_delegated_transaction();

try {
    // Insert record
    $recordid = $DB->insert_record('your_table', $dataobject);
    
    // Update related records
    $DB->set_field('another_table', 'status', 1, ['recordid' => $recordid]);
    
    // Commit transaction
    $transaction->allow_commit();
} catch (\Exception $e) {
    $transaction->rollback($e);
    throw $e;
}

Working with Course Modules

// Create course module
$moduleid = $DB->get_field('modules', 'id', ['name' => 'quiz'], MUST_EXIST);

$cm = new \stdClass();
$cm->course = $courseid;
$cm->module = $moduleid;
$cm->instance = 0; // Will be updated after activity creation
$cm->visible = 1;
$cm->groupmode = 0;
$cmid = add_course_module($cm);

// Create activity instance (e.g., quiz)
$quiz = new \stdClass();
$quiz->course = $courseid;
$quiz->name = 'My Quiz';
$quiz->coursemodule = $cmid;
// ... other quiz fields ...

$quizid = quiz_add_instance($quiz, null);

// Update course module with instance ID
$DB->set_field('course_modules', 'instance', $quizid, ['id' => $cmid]);
course_add_cm_to_section($courseid, $cmid, 0);

Access Restrictions (Groups/Availability)

// Restrict activity to specific user via group
$groupname = 'activity_' . $activityid . '_user_' . $userid;

// Create or get group
if (!$groupid = $DB->get_field('groups', 'id', ['courseid' => $courseid, 'name' => $groupname])) {
    $groupdata = (object)[
        'courseid' => $courseid,
        'name' => $groupname,
        'timecreated' => time(),
        'timemodified' => time()
    ];
    $groupid = $DB->insert_record('groups', $groupdata);
}

// Add user to group
if (!$DB->record_exists('groups_members', ['groupid' => $groupid, 'userid' => $userid])) {
    $DB->insert_record('groups_members', (object)[
        'groupid' => $groupid,
        'userid' => $userid,
        'timeadded' => time()
    ]);
}

// Set availability condition
$restriction = [
    'op' => '&',
    'show' => false,
    'c' => [
        [
            'type' => 'group',
            'id' => $groupid
        ]
    ],
    'showc' => [false]
];

$DB->set_field('course_modules', 'availability', json_encode($restriction), ['id' => $cmid]);

Random Question Selection with Tags

private static function get_random_questions($categoryid, $tagname, $limit) {
    global $DB;
    
    $sql = "SELECT q.id
            FROM {question} q
            INNER JOIN {question_versions} qv ON qv.questionid = q.id
            INNER JOIN {question_bank_entries} qbe ON qbe.id = qv.questionbankentryid
            INNER JOIN {question_categories} qc ON qc.id = qbe.questioncategoryid
            JOIN {tag_instance} ti ON ti.itemid = q.id
            JOIN {tag} t ON t.id = ti.tagid
            WHERE LOWER(t.name) = :tagname
              AND qc.id = :categoryid
              AND ti.itemtype = 'question'
              AND q.qtype = 'multichoice'";
    
    $qids = $DB->get_fieldset_sql($sql, [
        'categoryid' => $categoryid,
        'tagname' => strtolower($tagname)
    ]);
    
    shuffle($qids);
    return array_slice($qids, 0, $limit);
}

Testing Your API

1. Via Moodle Web Services Test Client

1. Enable web services: Site administration > Advanced features
2. Enable REST protocol: Site administration > Plugins > Web services > Manage protocols
3. Create service: Site administration > Server > Web services > External services
4. Test function: Site administration > Development > Web service test client

2. Via curl

# Get token first
curl -X POST "https://yourmoodle.com/login/token.php" \
  -d "username=admin" \
  -d "password=yourpassword" \
  -d "service=moodle_mobile_app"

# Call your API
curl -X POST "https://yourmoodle.com/webservice/rest/server.php" \
  -d "wstoken=YOUR_TOKEN" \
  -d "wsfunction=local_yourplugin_your_api_name" \
  -d "moodlewsrestformat=json" \
  -d "userid=2" \
  -d "courseid=3"

3. Via JavaScript (AJAX)

require(['core/ajax'], function(ajax) {
    var promises = ajax.call([{
        methodname: 'local_yourplugin_your_api_name',
        args: {
            userid: 2,
            courseid: 3
        }
    }]);

    promises[0].done(function(response) {
        console.log('Success:', response);
    }).fail(function(error) {
        console.error('Error:', error);
    });
});

Common Pitfalls & Solutions

1. "Function not found" Error

Solution:

• Purge caches: Site administration > Development > Purge all caches
• Verify function name in services.php matches exactly
• Check namespace and class name are correct

2. "Invalid parameter value detected"

Solution:

• Ensure parameter types match between definition and usage
• Check required vs optional parameters
• Validate nested structure definitions

3. SQL Injection Vulnerabilities

Solution:

• Always use placeholder parameters (:paramname)
• Never concatenate user input into SQL strings
• Use Moodle's database methods: get_record(), get_records(), etc.

4. Permission Denied Errors

Solution:

• Call self::validate_context($context) early in execute()
• Check required capabilities match user's permissions
• Verify user has role assignments in the context

5. Transaction Deadlocks

Solution:

• Keep transactions short
• Always commit or rollback in finally blocks
• Avoid nested transactions

Debugging Checklist

• Check Moodle debug mode: Site administration > Development > Debugging
• Review web services logs: Site administration > Reports > Logs
• Check custom log files in $CFG->dataroot/local_yourplugin/
• Verify database queries using $DB->set_debug(true)
• Test with admin user to rule out permission issues
• Clear browser cache and Moodle caches
• Check PHP error logs on server

Plugin Structure Checklist

local/yourplugin/
├── version.php                 # Plugin version and metadata
├── db/
│   ├── services.php           # External service definitions
│   └── access.php             # Capability definitions (optional)
├── classes/
│   └── external/
│       ├── your_api_name.php  # External API implementation
│       └── another_api.php    # Additional APIs
├── lang/
│   └── en/
│       └── local_yourplugin.php  # Language strings
└── tests/
    └── external_test.php      # Unit tests (optional but recommended)

Examples from Real Implementation

Simple Read API (Get Quiz Attempts)

<?php
namespace local_userlog\external;

defined('MOODLE_INTERNAL') || die();
require_once("$CFG->libdir/externallib.php");

use external_api;
use external_function_parameters;
use external_single_structure;
use external_value;

class get_quiz_attempts extends external_api {
    public static function execute_parameters() {
        return new external_function_parameters([
            'userid' => new external_value(PARAM_INT, 'User ID'),
            'courseid' => new external_value(PARAM_INT, 'Course ID')
        ]);
    }

    public static function execute($userid, $courseid) {
        global $DB;

        self::validate_parameters(self::execute_parameters(), [
            'userid' => $userid,
            'courseid' => $courseid
        ]);

        $sql = "SELECT COUNT(*) AS quiz_attempts
                FROM {quiz_attempts} qa
                JOIN {quiz} q ON qa.quiz = q.id
                WHERE qa.userid = :userid AND q.course = :courseid";

        $attempts = $DB->get_field_sql($sql, [
            'userid' => $userid,
            'courseid' => $courseid
        ]);

        return ['quiz_attempts' => (int)$attempts];
    }

    public static function execute_returns() {
        return new external_single_structure([
            'quiz_attempts' => new external_value(PARAM_INT, 'Total number of quiz attempts')
        ]);
    }
}

Complex Write API (Create Quiz from Categories)

See attached create_quiz_from_categories.php for a comprehensive example including:

• Multiple database insertions
• Course module creation
• Quiz instance configuration
• Random question selection with tags
• Group-based access restrictions
• Extensive error logging
• Transaction management

Quick Reference: Common Moodle Tables

Additional Resources

• Moodle External API Documentation
• Moodle Coding Style
• Moodle Database API
• Web Services API Documentation

Guidelines

• Always validate input parameters using validate_parameters()
• Check user context and capabilities before operations
• Use parameterized SQL queries (never string concatenation)
• Implement comprehensive error handling and logging
• Follow Moodle naming conventions (lowercase, underscores)
• Document all parameters and return values clearly
• Test with different user roles and permissions
• Consider transaction safety for write operations
• Purge caches after service registration changes
• Keep API methods focused and single-purpose