diff --git a/src/Controller/GraphController.php b/src/Controller/GraphController.php
index 6d716c9..9861041 100644
--- a/src/Controller/GraphController.php
+++ b/src/Controller/GraphController.php
@@ -34,8 +34,12 @@ final class GraphController
     }
 
     /**
-     * Query parameters:
-     *   theme  string  dark|light (default: dark)
+     * Serves the contribution heatmap SVG, from a 1-hour cache on repeat requests.
+     *
+     * Rejects requests to disallowed hosts (ALLOWED_HOSTS env) with a 403.
+     *
+     * @param  Request $request query parameter `theme` selects "dark" (default) or "light"
+     * @return Response image/svg+xml body, cacheable for 3600s
      */
     #[Route('/graph.svg', name: 'contribution_graph', methods: ['GET'])]
     public function graph(Request $request): Response
@@ -66,6 +70,12 @@ final class GraphController
         ]);
     }
 
+    /**
+     * Redirects "/" to "/graph.svg", forwarding any query string (e.g. ?theme=light).
+     *
+     * @param  Request          $request incoming request whose query string is preserved
+     * @return RedirectResponse 302 redirect to /graph.svg
+     */
     #[Route('/', name: 'index', methods: ['GET'])]
     public function index(Request $request): RedirectResponse
     {
@@ -75,6 +85,12 @@ final class GraphController
         return new RedirectResponse($url, 302);
     }
 
+    /**
+     * Reports per-provider connectivity status as JSON.
+     *
+     * @return Response 200 with {"status":"ok",...} or 503 with {"status":"degraded",...}
+     *                  when any configured provider's probe reports an error
+     */
     #[Route('/health', name: 'health', methods: ['GET'])]
     public function health(): Response
     {
diff --git a/src/Entity/Contribution.php b/src/Entity/Contribution.php
index 2e05227..3472cc6 100644
--- a/src/Entity/Contribution.php
+++ b/src/Entity/Contribution.php
@@ -4,8 +4,14 @@ declare(strict_types=1);
 
 namespace GitContributionGraph\Entity;
 
+/** A single provider's contribution count for one day, as stored in {@see \GitContributionGraph\Service\ContributionStore}. */
 final class Contribution
 {
+    /**
+     * @param string $provider provider identifier, e.g. "github"
+     * @param int    $date     day of the contribution, as a unix timestamp
+     * @param int    $count    contribution count for that day
+     */
     public function __construct(
         public readonly string $provider,
         public readonly int $date,
diff --git a/src/Service/ContributionStore.php b/src/Service/ContributionStore.php
index c793b19..5effcbf 100644
--- a/src/Service/ContributionStore.php
+++ b/src/Service/ContributionStore.php
@@ -15,6 +15,9 @@ class ContributionStore
 
     /**
      * Opens (creating if needed) the SQLite store at $dbPath and ensures the schema exists.
+     *
+     * @param string $dbPath        filesystem path to the SQLite database file
+     * @param ?int   $retentionDays days of history to keep; null or 0 keeps rows forever
      */
     public function __construct(
         private readonly string $dbPath = "%kernel.project_dir%/var/data/contributions.db",
@@ -43,6 +46,10 @@ class ContributionStore
 
     /**
      * Inserts a contribution count, overwriting any existing count for the same provider/date.
+     *
+     * @param string $provider provider identifier, e.g. "github"
+     * @param int    $unixtime day of the contribution, as a unix timestamp
+     * @param int    $count    contribution count for that day
      */
     public function add(string $provider, int $unixtime, int $count): void
     {
@@ -56,6 +63,9 @@ class ContributionStore
 
     /**
      * Deletes the contribution row for the given provider/date, if any.
+     *
+     * @param string $provider provider identifier, e.g. "github"
+     * @param int    $unixtime day to delete, as a unix timestamp
      */
     public function remove(string $provider, int $unixtime): void
     {
@@ -69,7 +79,8 @@ class ContributionStore
     /**
      * Upserts a batch of date => count pairs for a provider via repeated add() calls.
      *
-     * @param array<int, int> $dateCounts unix timestamp => count
+     * @param string           $provider   provider identifier, e.g. "github"
+     * @param array<int, int>  $dateCounts unix timestamp => count
      */
     public function merge(string $provider, array $dateCounts): void
     {
@@ -80,6 +91,9 @@ class ContributionStore
 
     /**
      * Returns the most recent stored unix timestamp for a provider, or null if it has no rows.
+     *
+     * @param  string $provider provider identifier, e.g. "github"
+     * @return ?int   unix timestamp of the latest stored day, or null if none stored yet
      */
     public function latestDate(string $provider): ?int
     {
@@ -92,6 +106,10 @@ class ContributionStore
 
     /**
      * Returns all stored contributions for a provider, optionally limited to the last $sinceDays days.
+     *
+     * @param  string $provider  provider identifier, e.g. "github"
+     * @param  ?int   $sinceDays if set, only rows from the last N days are returned
+     * @return ContributionCollection
      */
     public function all(string $provider, ?int $sinceDays = null): ContributionCollection
     {
@@ -106,9 +124,12 @@ class ContributionStore
         $stmt = $this->pdo->prepare($sql);
         $stmt->execute($params);
 
+        /** @var array<int, array{provider: string, date: int|string, count: int|string}> $rows */
+        $rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
+
         $contributions = array_map(
             static fn(array $row): Contribution => new Contribution($row['provider'], (int) $row['date'], (int) $row['count']),
-            $stmt->fetchAll(PDO::FETCH_ASSOC),
+            $rows,
         );
 
         return new ContributionCollection(...$contributions);
diff --git a/src/Service/Provider/ProbeTrait.php b/src/Service/Provider/ProbeTrait.php
index df3ae4e..194261a 100644
--- a/src/Service/Provider/ProbeTrait.php
+++ b/src/Service/Provider/ProbeTrait.php
@@ -9,6 +9,10 @@ use Symfony\Contracts\HttpClient\Exception\TransportExceptionInterface;
 
 trait ProbeTrait
 {
+    /**
+     * Reports NotConfigured if credentials are missing, otherwise pings the provider
+     * and reports Ok or Error (with a classified error code and message).
+     */
     public function probe(): ProviderStatus
     {
         if (!$this->isConfigured()) {
diff --git a/src/Service/Provider/ProviderHealthChecker.php b/src/Service/Provider/ProviderHealthChecker.php
index c4a4f85..c81838f 100644
--- a/src/Service/Provider/ProviderHealthChecker.php
+++ b/src/Service/Provider/ProviderHealthChecker.php
@@ -8,13 +8,17 @@ use Symfony\Component\DependencyInjection\Attribute\AutowireIterator;
 
 final class ProviderHealthChecker
 {
+    /** @param iterable<ProviderInterface> $providers */
     public function __construct(
         #[AutowireIterator('app.provider')]
         private readonly iterable $providers,
     ) {}
 
     /**
-     * @return array{status: string, providers: array<string, array<string, string>>}
+     * Probes every configured provider and aggregates the results for the /health endpoint.
+     *
+     * @return array{status: string, providers: array<string, array<string, string>>} 'status' is
+     *   "degraded" if any provider's probe() reported an error, otherwise "ok"
      */
     public function check(): array
     {
diff --git a/src/Service/Provider/ProviderStatus.php b/src/Service/Provider/ProviderStatus.php
index 7ae1517..bfcd0c4 100644
--- a/src/Service/Provider/ProviderStatus.php
+++ b/src/Service/Provider/ProviderStatus.php
@@ -4,8 +4,15 @@ declare(strict_types=1);
 
 namespace GitContributionGraph\Service\Provider;
 
+/** Result of probing a single provider, as reported by the /health endpoint. */
 final class ProviderStatus
 {
+    /**
+     * @param string              $name    provider identifier, e.g. "github"
+     * @param ProviderStatusType  $status  overall outcome of the probe
+     * @param ?ProviderErrorCode  $error   classified error code, set only when $status is Error
+     * @param ?string             $message human-readable error detail, set only when $status is Error
+     */
     public function __construct(
         public readonly string $name,
         public readonly ProviderStatusType $status,
@@ -13,7 +20,11 @@ final class ProviderStatus
         public readonly ?string $message = null,
     ) {}
 
-    /** @return array<string, string> */
+    /**
+     * Converts to the array shape used in the /health JSON response, omitting error/message when unset.
+     *
+     * @return array<string, string>
+     */
     public function toArray(): array
     {
         $data = ['status' => $this->status->value];
diff --git a/src/Service/Renderer/SvgRenderer.php b/src/Service/Renderer/SvgRenderer.php
index ab215ce..0c48db2 100644
--- a/src/Service/Renderer/SvgRenderer.php
+++ b/src/Service/Renderer/SvgRenderer.php
@@ -36,6 +36,12 @@ final class SvgRenderer
     private const MARGIN_Y  = 20;   // top margin for month labels
     private const PADDING   = 10;   // outer padding
 
+    /**
+     * Builds the full self-contained SVG heatmap for a contribution map.
+     *
+     * @param array<string, int> $contributions date (Y-m-d) => contribution count
+     * @param string             $theme         "dark" or "light"; unknown values fall back to "dark"
+     */
     public function render(array $contributions, string $theme = 'dark'): string
     {
         $colors = self::THEMES[$theme] ?? self::THEMES['dark'];
@@ -91,6 +97,9 @@ final class SvgRenderer
     /**
      * Builds a [week][day] grid where each cell is ['date' => 'Y-m-d', 'count' => int]
      * or null if the date is in the future.
+     *
+     * @param  array<string, int> $contributions date (Y-m-d) => contribution count
+     * @return array<int, array<int, array{date: string, count: int}|null>>
      */
     private function buildGrid(\DateTimeImmutable $start, \DateTimeImmutable $today, array $contributions): array
     {
@@ -125,6 +134,10 @@ final class SvgRenderer
         };
     }
 
+    /**
+     * @param  array<string, int> $contributions date (Y-m-d) => contribution count
+     * @return array{total: int}
+     */
     private function computeStats(array $contributions): array
     {
         return ['total' => array_sum($contributions)];
@@ -132,6 +145,7 @@ final class SvgRenderer
 
     // -------------------------------------------------------------------------
 
+    /** @param array<int, array<int, array{date: string, count: int}|null>> $grid */
     private function renderMonthLabels(array $grid, string $textColor): string
     {
         $out       = '';
@@ -183,6 +197,10 @@ final class SvgRenderer
         return $out;
     }
 
+    /**
+     * @param array<int, array<int, array{date: string, count: int}|null>> $grid
+     * @param array{bg: string, text: string, levels: array<int, string>}  $colors
+     */
     private function renderCells(array $grid, array $colors): string
     {
         $out = '';
@@ -218,6 +236,7 @@ final class SvgRenderer
         return $out;
     }
 
+    /** @param array{bg: string, text: string, levels: array<int, string>} $colors */
     private function renderLegend(int $totalH, array $colors): string
     {
         $y   = $totalH - 14;
diff --git a/tests/Unit/Service/Renderer/SvgRendererTest.php b/tests/Unit/Service/Renderer/SvgRendererTest.php
index 705bd79..ab8f6cc 100644
--- a/tests/Unit/Service/Renderer/SvgRendererTest.php
+++ b/tests/Unit/Service/Renderer/SvgRendererTest.php
@@ -54,6 +54,7 @@ final class SvgRendererTest extends TestCase
         $this->assertStringContainsString($expectedColor, $svg);
     }
 
+    /** @return iterable<string, array{string, string}> */
     public static function theme_background_provider(): iterable
     {
         yield 'dark theme'    => ['dark',    '#0d1117'];
@@ -97,6 +98,7 @@ final class SvgRendererTest extends TestCase
         $this->assertStringContainsString('>' . $label . '<', $svg);
     }
 
+    /** @return iterable<string, array{string}> */
     public static function day_of_week_label_provider(): iterable
     {
         yield 'Monday'    => ['Mon'];