Building a Headless CMS API with ProcessWire

Organizing Content Delivery via ProcessWire API

A ProcessWire project has been running for several years, with dozens of templates accumulated. Then the client demands a React SPA or mobile app. Standard PHP rendering won't work—they need clean JSON. You could hack together something with direct DB access, but that breaks permission logic and caching. The right solution is to add an HTTP API on top of the existing templates. We do this in 2–4 days using built-in tools: a template router or the GraphQL module. No rewriting—just a new endpoint.

We have completed over 30 such projects. The most loaded configuration handles up to 100,000 requests per day on a budget VPS. The API has been running without issues for over two years. Below we break down the implementation options.

Built-in PHP API

ProcessWire exposes $pages, $page, $user, and $config as global variables in templates:

// templates/blog.php

// Selection with filters and pagination
$limit = 12;
$start = ($input->pageNum - 1) * $limit;

$posts = $pages->find("template=blog-post, status=published, sort=-date, limit=$limit, start=$start");
$totalPosts = $pages->count("template=blog-post, status=published");

// Selection with field conditions
$featuredPosts = $pages->find("
  template=blog-post,
  featured=1,
  date>=today,
  category.name%=Web Development,
  sort=-date,
  limit=3
");

// Single item
$post = $pages->get("template=blog-post, slug=my-post-slug");
if (!$post->id) wire404();

For a full ProcessWire JSON API, we create custom REST endpoints using ProcessWire API templates, enabling seamless headless ProcessWire SPA development.

Selector String — Query Language

// Text search
$pages->find("template=product, title*=laptop, sort=title");

// Numeric conditions
$pages->find("template=product, price>=1000, price<=5000");

// Date
$pages->find("template=event, event_date>=today, sort=event_date");

// OR conditions
$pages->find("template=post, (category=tech|category=science)");

// Related pages
$pages->find("template=product, categories.id={$category->id}");

// Full-text search
$pages->find("title|body~=search query, template=post");

// Sort by custom field
$pages->find("template=product, sort=-rating, sort=title");

REST API via ProCache or Custom Module

ProcessWire does not ship with a built-in REST API. We create one using a template router:

// site/templates/api.php
// URL: /api/blog/?page=1&limit=10

header('Content-Type: application/json');
header('Access-Control-Allow-Origin: ' . $config->httpHost);

// Simple key-based authorization
$apiKey = $input->get->text('key');
if ($apiKey !== $config->apiKey) {
    http_response_code(401);
    echo json_encode(['error' => 'Unauthorized']);
    return;
}

$page_num = (int) $input->get->int('page') ?: 1;
$limit = min((int) $input->get->int('limit') ?: 10, 100);
$start = ($page_num - 1) * $limit;

$posts = $pages->find("
    template=blog-post,
    status=published,
    sort=-date,
    limit=$limit,
    start=$start
");

$result = [
    'data'  => array_map(fn($post) => [
        'id'      => $post->id,
        'title'   => $post->title,
        'slug'    => $post->name,
        'url'     => $post->url,
        'date'    => $post->date->format('Y-m-d'),
        'excerpt' => $post->excerpt,
        'image'   => $post->image ? [
            'url'    => $post->image->width(800)->url,
            'width'  => 800,
            'height' => (int) round(800 / $post->image->ratio),
        ] : null,
    ], $posts->getArray()),
    'total' => $posts->getTotal(),
    'page'  => $page_num,
    'limit' => $limit,
];

echo json_encode($result);

ProcessWire GraphQL Module

Install via ProcessWire modules. Download from processwire.com/modules/processwire-graphql/ and add settings to config.php:

$config->graphql = [
    'templateFilters' => ['blog-post', 'product', 'category'],
    'fieldFilters'    => ['title', 'body', 'date', 'image', 'category'],
    'maxLimit'        => 100,
];

query {
  blogPost(s: "status=published, sort=-date, limit=10") {
    list {
      id
      title
      date
      body
      image { url(width: 800) }
      category { title url }
    }
    total
  }
}

Response Caching

// Caching via WireCache
$cacheKey = "api_posts_page{$page_num}";
$cached = $cache->get($cacheKey);

if ($cached) {
    echo $cached;
    return;
}

// ... build $result ...
$json = json_encode($result);
$cache->save($cacheKey, $json, 3600); // 1 hour
echo $json;

Building a basic REST API on ProcessWire (5–7 endpoints) takes 2–4 days. Typical investment: a basic REST API starts at $2,500, including caching and documentation. GraphQL integration adds $500–$1,500. Cost is determined after analyzing the project scope. Typical costs range from $3,000 to $5,000, and our approach saves you 30–40% compared to alternative CMS migrations.

REST vs GraphQL for ProcessWire

REST is better when you need minimal response and full control. GraphQL is preferable if clients need flexible field selection.

ProcessWire as a Headless CMS: Advantages

Unlike WordPress (where an API is a bolt-on hack) or Strapi (heavy), ProcessWire provides a single source of truth for both PHP templates and external clients. You write templates once, and the JSON output is just a second template with different headers. According to our estimates, this reduces maintenance costs by 30–40%.

ProcessWire API documentation confirms that selectors work identically in templates and API.

What Is Included in ProcessWire API Setup

Deliverables:

• API documentation (Postman/OpenAPI)
• Access to staging environment
• 1-hour training session for your developers
• 30 days of post-deployment support
• Source code and deployment scripts

How We Do It: Phases

1. Analysis: Study the template and field structure; determine required endpoints.
2. Design: Map the data schema and decide what to expose to the client.
3. Implementation: Write the template router or configure GraphQL; set up caching.
4. Testing: Verify all endpoints; perform load testing (100 concurrent requests).
5. Deployment: Push to production server; set up monitoring.

We guarantee the result: if the API is not working after 4 days, we finish it free of charge. Experience: 30+ ProcessWire projects.

A ProcessWire REST API is developed 2–3 times faster than on WordPress with plugins, thanks to the unified selector syntax.

Our Edge: 30+ ProcessWire API Projects

With 7+ years of ProcessWire expertise, 30+ projects, and 5+ years on the market, we have proven experience. Over the years of working with ProcessWire, we have built APIs for e-commerce platforms, SaaS services, and content portals. We know the non-obvious constraints: PermissionManager behavior in headless mode, ProCache nuances with Bearer tokens, and fieldgroup peculiarities when serializing nested objects. The most loaded configuration from our practice handles 100,000 requests per day on a 4 GB RAM server without degradation. We are ready to take on any complexity: from a basic REST API with five endpoints to GraphQL with persisted queries and real-time subscriptions. Send us a description of your project—we will propose the optimal stack and estimate the work within one business day.

With over 7 years of ProcessWire development experience and 30+ completed API projects, we ensure reliable delivery. Get a consultation for your project—contact us and we will provide an estimate within one day.

API Development with REST, GraphQL, WebSocket, and tRPC

A client comes to us with a Postman collection of 200 endpoints and says: 'Everything works, but the frontend is slow.' We open the Network tab — 47 sequential requests to load one dashboard page. Each one waits for the previous. This is not a server speed issue — it's an API architecture problem. With 10 years on the market, we've redesigned dozens of such integrations, and we guarantee: the right protocol and contract solve the problem at its root.

When REST stops being enough

REST works well for simple CRUD operations. But as soon as a mobile app appears alongside the web interface, over-fetching begins: the mobile app requests /api/users/123 and gets a 4KB object, but only needs name and avatar. Multiply that by a list of 50 users — 200KB traffic instead of 8KB.

GraphQL solves this with selection sets. The client describes exactly the fields it needs, and the server returns only those. On a project with React Native + Next.js, we migrated from REST to Apollo Server: payload size on the main screen dropped from 340KB to 28KB — a 92% traffic savings. Our certified engineers confirm: the typical pain when adopting GraphQL is N+1 query. A resolver for the author field on a post calls SELECT * FROM users WHERE id = ? for each post in the list. On a page with 20 posts — 21 database queries. Solved with DataLoader — it batches queries and turns them into one SELECT * FROM users WHERE id IN (...).

What is tRPC and how is it better than REST/GraphQL?

If the entire stack is TypeScript (Next.js + Node/Bun), tRPC removes a whole layer of problems. You define a procedure on the server — the client gets full type-safety automatically, without code generation and without Swagger. Renamed a field in the Zod schema — TypeScript highlights all places on the frontend where it's used. tRPC reduces code by 2 times compared to REST + Swagger + openapi-typescript: no need to maintain a separate specification and generate types — everything is inferred from runtime validators. However, tRPC is not suitable if the API is consumed by third-party clients or mobile apps in other languages — in such cases we use GraphQL or REST with OpenAPI specification.

WebSocket and real-time: when SSE, when WS?

HTTP polling every 5 seconds is an illusion of real-time with up to 5 seconds delay and useless server load. For chats, live notifications, collaborative editing — WebSocket or Server-Sent Events. SSE is a one-way stream from server to client, works over ordinary HTTP, automatically reconnects. Suitable for notifications, data streaming, progress bars. WebSocket is bidirectional, needed for chats and collaborative features. Experience shows: 80% of 'real-time' tasks are solved with SSE, not WebSocket — fewer infrastructure complexities.

A typical mistake: opening a WebSocket connection for each page component. On one project, the dashboard opened 12 parallel WS connections. The correct approach is one connection manager at the application level, subscriptions through it. In our work results, we always transfer the connection scheme and a ready solution.

Swagger / OpenAPI as a contract

Documentation written after the fact becomes outdated the day after release. We write the OpenAPI 3.1 specification before development starts; it becomes the contract between frontend and backend. The frontend generates types via openapi-typescript, the backend validates incoming data using generated schemas. Contract deviation from implementation is caught on CI, not during review. For Laravel — l5-swagger or dedoc/scramble. For Node.js — @fastify/swagger or Zod + zod-to-openapi.

How to properly authenticate an API?

JWT with long-lived access tokens without rotation is a source of problems when compromised. The correct scheme: access token for 15 minutes, refresh token for 30 days with rotation on each use. Refresh token stored in an httpOnly cookie, access token in memory (not in localStorage). For inter-service communication — API Keys with scope limitations or mTLS. OAuth 2.0 with PKCE for public clients (SPA, mobile).

How to handle versioning and backward compatibility?

Breaking changes in an API without versioning break clients. Three approaches we use in projects:

We guarantee backward compatibility through automated checks (oasdiff) on CI.

How we develop APIs: step-by-step plan

1. Analysis — audit of current integrations, data schema compilation, protocol selection (REST/GraphQL/tRPC/WebSocket).
2. Contract design — OpenAPI or SDL (GraphQL) before the first line of code.
3. Development — implementation per contract, unit tests for each endpoint.
4. Load testing — k6: 500 virtual users, 10 minutes, p95 latency ≤ 200ms.
5. Deployment — CI/CD with backward compatibility check, automatic documentation publication.
6. Team training — handover of Postman collection or Playground, connection instructions.

What is included (deliverables)

• OpenAPI 3.1 specification (or SDL for GraphQL).
• Generated client types for TypeScript / Dart / Kotlin.
• Set of automated tests covering all endpoints (unit + integration).
• Load tests (k6) and report (p50/p95/p99 latency, RPS).
• Documentation in Swagger UI / Redoc / GraphiQL.
• Team training (2–4 hour workshop).
• Support for 30 days after delivery (per contract).

Our experience

• 10+ years in the API development market.
• 200+ completed projects (REST, GraphQL, WebSocket, tRPC).
• 50+ certified engineers (AWS, Kubernetes, API Design).
• Traffic savings averaging 85% when migrating from REST to GraphQL for mobile apps.
• 100% backward compatibility — not a single broken client in the last 3 years.

Timeline

API development for a typical SaaS project with 30–50 endpoints: from 3 to 8 weeks depending on business logic complexity and number of external integrations. Migration of an existing REST API to GraphQL: from 2 to 6 weeks. Adding a WebSocket layer to an existing backend: from 1 to 3 weeks. Cost is calculated individually after an audit. Get a consultation — contact us to discuss your project.