There is no defensible, current 11-product ranking from the available official documentation. Five services are documented well enough to compare: Firebase Realtime Database, Supabase Realtime, AWS AppSync, Ably and PubNub. They solve different problems. Choose a realtime database when clients must stay synchronized with stored application data; choose a managed Pub/Sub service for chat, presence or custom events; choose AppSync when GraphQL and AWS-managed connections fit your stack.
The guide below compares those five without inventing prices, benchmarks or unsupported entries. A section near the end explains how to evaluate additional vendors before committing to an eleven-item shortlist.
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What “real-time application” means in practice
Real-time does not describe one architecture. A dashboard may subscribe to database changes, a chat system may publish messages and presence events, and a collaborative editor may broadcast cursor positions without persisting every event. Start by identifying the event that must arrive quickly, the data that must be durable, and whether clients need offline recovery.
- Database synchronization: clients observe changes to shared records and can resume after a connection interruption.
- Change feeds: a service emits inserts, updates or deletes from an existing database.
- GraphQL subscriptions: clients receive updates through a schema and subscription operation.
- Managed Pub/Sub: publishers and subscribers exchange events through channels while the provider handles persistent connections and scaling.
These categories overlap, but they have different security, data-model and cost consequences. Do not select a product solely because its documentation uses the word “real-time.”
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At-a-glance comparison
| Service | Primary architecture | Best fit | Data model | Important qualification |
|---|---|---|---|---|
| Firebase Realtime Database | Realtime database synchronization | Applications whose clients share a JSON-shaped state tree | Cloud-hosted JSON/NoSQL | Google directs teams needing richer queries, scalability and higher availability to consider Cloud Firestore. |
| Supabase Realtime | Broadcast, Presence and Postgres Changes | Postgres-backed products needing custom events, presence or database updates | Relational/Postgres-oriented, plus channel events | Private channels with row-level security are recommended for production; Postgres Changes is mainly for quick tests or low connected-user counts. |
| AWS AppSync | GraphQL subscriptions and AppSync Events WebSocket Pub/Sub | Teams already using AWS or wanting managed GraphQL/event APIs | GraphQL schema over connected data sources | AppSync Events is documented as available from March 13, 2025; AWS manages subscription connections and scaling. |
| Ably | Managed cloud Pub/Sub with higher-level products | Custom event distribution, or products such as chat built on a messaging platform | Channel/message model layered over your data sources | Ably says interface, persistent connections, feature complexity and pricing implications should drive the choice. |
| PubNub | Managed publish/subscribe messaging | Cross-device and cross-platform realtime messaging through SDKs | Messages and channels | The available documentation does not establish comparative prices, limits or independently measured latency. |
1. Firebase Realtime Database
Firebase Realtime Database is a cloud-hosted NoSQL database that stores JSON and synchronizes it to connected clients. It is a natural fit when the authoritative state is already a tree of documents or objects and the client should observe updates without building a separate message pipeline.
Where it fits
- Shared application state such as a live score, status board or lightweight collaboration model.
- Clients that need local persistence and synchronization after reconnecting; Firebase documents both behaviors.
- Teams comfortable expressing authorization as database read and write rules, optionally combined with Firebase Authentication.
Where to be cautious
A JSON tree can become awkward when the application needs richer data modeling or complex querying. Google’s documentation specifically points modern applications needing richer data models, queryability, scalability and higher availability toward Cloud Firestore. That is a data-model decision, not a blanket claim that one Firebase database is always better.
Read the Firebase Realtime Database documentation for the synchronization, offline and rules model.
2. Supabase Realtime
Supabase Realtime exposes three distinct mechanisms, so “Supabase realtime” should not be treated as one feature.
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Broadcast
Broadcast sends low-latency custom events between clients. It suits transient interactions such as cursor movement, typing indicators or game actions where the event is not itself a database row.
Presence
Presence shares user state, for example who is online or which document a user has open. Supabase warns that Presence has computational overhead and recommends using it minimally. Do not use presence as a substitute for durable activity records.
Rank #2
Postgres Changes
Postgres Changes lets clients listen for inserts, updates and deletes in Postgres. Supabase characterizes it as most suitable for quick testing or low connected-user counts; high-fan-out production designs should evaluate the operational effect before adopting it broadly.
Authorization and setup
The setup guidance recommends private channels and row-level security (RLS) policies for production authorization. Treat channel membership and database policy design as part of the application threat model, not as a final configuration task. The feature guide and getting-started guide cover the three mechanisms and their setup.
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AWS AppSync is a managed service for GraphQL and Pub/Sub APIs. GraphQL subscriptions create and maintain secure WebSocket connections for live updates, while AWS manages connection handling and scaling requirements.
GraphQL subscription fit
Choose this path when your clients already consume a GraphQL schema and a change should be delivered as a typed subscription result. The schema becomes the contract between producers and clients, which can reduce ad-hoc event formats but adds GraphQL design and AWS integration work.
AppSync Events
AWS documentation describes AppSync Events as a WebSocket-powered Pub/Sub API and dates its availability to March 13, 2025. It is relevant when you need event channels without modeling every interaction as a GraphQL data fetch.
Selection cautions
AppSync is an editorial fit for AWS-centered teams, not proof that AWS is automatically cheaper or simpler. AWS describes charges based on API requests and delivered realtime messages; verify the current pricing page and model your own connection and message patterns before choosing it. Start with the AWS AppSync service documentation and its realtime data guide.
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4. Ably
Ably provides cloud Pub/Sub and higher-level products such as Chat. The lower-level service is appropriate when your application owns the domain model and needs reliable channel-based event distribution; a higher-level product can reduce the amount of chat-specific behavior you build yourself.
Questions to answer before selecting it
- What latency target does each interaction require?
- Which connections remain open, and for how long?
- Do you need broadcast only, or presence, history and chat semantics?
- Which existing data sources and client platforms must integrate?
- How will connection and message volume affect the bill?
Ably’s guidance says these interface, persistent-connection, feature-complexity, integration and pricing considerations determine the appropriate product. Its reliability, scale and performance statements are vendor claims rather than independent benchmarks. See the platform overview and product guidance.
5. PubNub
PubNub documents SDKs and publish/subscribe messaging for realtime applications across devices and platforms. It is a managed messaging candidate when you want channel-based delivery without operating your own WebSocket fleet.
Evaluate the integration, not just the SDK list
- Confirm that an SDK supports every client platform you ship and the authentication flow you require.
- Define which messages are transient and which must be written to your own durable store.
- Specify authorization boundaries for channels before exposing publish or subscribe capabilities.
- Load-test your actual fan-out and reconnect pattern; the available documentation does not establish an independent latency or capacity comparison.
Use the PubNub documentation for current SDK and messaging details. Do not infer comparative pricing, limits or performance from the documentation alone.
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How to choose among the five
Choose by source of truth
If the database is the source of truth and clients should mirror records, begin with Firebase Realtime Database, Supabase Postgres Changes or AppSync subscriptions. If events are ephemeral and should not become rows, begin with Supabase Broadcast, Ably Pub/Sub or PubNub.
Choose by data model
- JSON/NoSQL state tree: Firebase Realtime Database.
- Postgres plus channels: Supabase Realtime.
- Typed API contract: AWS AppSync.
- Existing data sources with a messaging layer: Ably or PubNub.
Choose by offline requirements
Firebase explicitly documents local persistence and synchronization after reconnecting. For the other services, verify the SDK’s offline queueing and replay semantics for your target clients rather than assuming that every managed channel behaves like a database cache.
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Choose by authorization boundary
Decide whether authorization is enforced by database rules, RLS policies, GraphQL resolvers, or channel tokens. Test unauthorized subscribe, publish and read attempts as separate cases. A valid WebSocket connection must not imply access to every event.
Choose by cost model
Do not compare a database product’s storage and read/write costs directly with a Pub/Sub product’s connection and message costs. AWS explicitly identifies API requests and delivered realtime messages as charge dimensions, and Ably notes pricing implications in product selection. Obtain current vendor pricing and estimate peak concurrent connections, messages per second, fan-out, retained data and reconnect storms.
Implementation checklist for a production realtime feature
- Write an event contract: name, payload, producer, consumers, ordering expectations and whether it is durable.
- Separate durable state from transient signals such as typing, cursor or presence events.
- Define authentication and authorization for every channel, row, subscription or resolver.
- Specify reconnect behavior, duplicate handling and what happens when a client was offline.
- Instrument connection count, subscribe failures, publish failures, delivery lag and client retry rates.
- Test burst fan-out, slow clients, expired credentials, network changes and service-side throttling.
- Model costs using your expected peak, not only average daily traffic.
Troubleshooting common failures
Clients connect but receive nothing
Check that the client subscribed to the exact channel, table filter or GraphQL operation, then verify authorization separately. Log the server-side publish result and the client’s subscription acknowledgment.
Updates appear twice
Reconnect logic may create duplicate subscriptions, or a durable database change may be delivered in addition to a broadcast event. Give events an identifier, make handlers idempotent and remove old listeners before retrying.
Users disappear during short network changes
Presence is usually connection-scoped. Add a reconnect grace period in the UI and define server-side expiry semantics; do not treat a momentary disconnect as an intentional logout.
Offline edits conflict after reconnect
Choose a conflict policy before shipping: last-write-wins, version checks, a merge function or an explicit user resolution. Firebase documents local persistence and later synchronization, but your application still needs a policy for concurrent edits.
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Costs rise unexpectedly
Look for high-fan-out broadcasts, reconnect storms, unbounded presence updates and clients subscribed to data they do not display. Move ephemeral signals to an appropriate Pub/Sub path and narrow database or GraphQL filters.
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Why this is not an honest 11-item ranking
The documented evidence supports five distinct services, not eleven comparable products. It does not provide a complete market survey, independent head-to-head benchmarks, all current prices or verified partner terms. Treat the five above as an evidence-backed starting set. To publish an eleven-item comparison, apply the same architecture, feature-fit, data-model, connection, client, security, offline and cost checks to six additional products using their current official documentation, then label subjective judgments separately from sourced facts.
Frequently Asked Questions
Do all realtime tools require WebSockets?
No. Managed services may use WebSockets or abstract connection handling behind SDKs and APIs. Verify the transport and reconnect behavior documented for the product and client you plan to use.
Should transient events be stored in the database?
Usually not. Store business records that must survive reconnects; use broadcast or Pub/Sub for ephemeral signals such as typing and cursor movement, unless your product explicitly needs an audit trail.
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Yes, but plan for a dual model: keep durable state in a database, define stable event contracts, and migrate producers and consumers independently so clients do not depend on vendor-specific payloads.
The Bottom Line
Start with the architecture that matches your source of truth: Firebase for synchronized JSON state, Supabase for Postgres plus channel features, AppSync for managed GraphQL or AWS Pub/Sub, and Ably or PubNub for a dedicated messaging layer. Validate authorization, reconnect behavior and usage-based cost with your own workload before committing.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
