When developers talk about calendar integrations, they usually describe the experience as “inconsistent,” “messy,” or “surprisingly complicated.” All true — but none of those words describe the real problem.

The problem isn’t that Google, Outlook and Apple Calendar behave differently.
 The problem is that they behave differently by design.

The more you learn about each vendor’s event model, the clearer it becomes: these systems were never meant to interoperate cleanly. They were built years apart, with different assumptions, different priorities, and entirely different underlying structures. Anyone trying to unify them ends up fighting the foundations, not the surface issues.

Let’s break down why.

1. They don’t share a common event model

Google’s model is loosely based on RFC5545, but it extends and relaxes large parts of it. Outlook uses Exchange semantics and serialisation, which resolve recurrence and timezones differently. Apple’s model is closest to ICS, yet behaves unpredictably around recurring events and attendee updates.

None of these systems exposes a strict, shared representation of an event. Even when all three accept ICS, they don’t interpret it the same way. It’s like trying to make three programming languages execute the same script without a compiler.

This is one of the core reasons Synara converts JSCalendar → ACE internally. Without a stable, internal representation, everything eventually falls apart.

2. Recurrence rules diverge in ways you can’t patch around

Every vendor supports recurrence, but none supports it in the same way.

• Google expands recurrence aggressively
• Outlook is strict and rejects ambiguous rules
• Apple sometimes alters recurrence when importing events
• ICS itself leaves interpretation details to the client

This makes round-tripping impossible. You can generate a rule, send it to all three, and end up with three slightly different events after import.

Synara solves this by giving you one stable recurrence model (ACE) and handling the conversion on its side. Without this barrier, developers end up writing per-vendor recurrence logic indefinitely.

3. Timezones behave differently depending on the client

Two recurring problems:

1. Some clients treat floating times as local; others as ambiguous
2. Some automatically rewrite timezone definitions; others keep them as-is

Even if you generate valid ICS with the correct VTIMEZONE block, there is no guarantee every client will apply it in the same way.

When Synara receives JSCalendar, it normalises timezone handling into ACE before anything else happens. This eliminates vendor-induced drift — a problem that normal ICS workflows can’t prevent.

4. RSVP behaviour is wildly inconsistent

Google may send a change notification.
 Outlook may update the event but send nothing.
 Apple might accept without broadcasting any change at all.

Two implications:

• You cannot rely on vendor-side updates.
• You cannot trust client-side updates to arrive consistently.

This is the main reason Synara sends every attendee response through ACE webhooks. You always know what happened, regardless of whether a client cooperated.

5. Webhooks are not a shared concept

Google has webhooks (sometimes).
 Microsoft has Graph notifications (often delayed).
 Apple has no webhook equivalent at all.

Even if you built three separate webhook systems, you’d still deal with:

• partial data
• different payload contracts
• random delays
• duplicate deliveries
• missing deliveries entirely

Synara’s single webhook layer gives you consistent event lifecycle updates even if the vendor never sends a thing.

6. ICS was never meant to reflect real-time state

ICS is a transport format, not a state container. It doesn’t handle:

• two-way updates
• real-time RSVPs
• versioning
• conflicts
• reconciling divergent states
• validating event integrity

Developers try to use ICS as if it were a database record. It isn’t — and that’s why so many systems break when clients mutate the ICS differently.

Synara uses ICS purely as a fallback output — not as a source of truth — and keeps ACE as the authoritative state.

Why Synara has to sit in the middle

A reliable, cross-vendor calendar layer cannot be built by patching over these differences.

You need:

• one input model (JSCalendar)
• one internal, stable event model (ACE)
• one webhook format
• one set of transformations
• one versioning system
• one conflict reconciliation strategy
• one canonical source of truth

That’s what Synara provides.

Without a compatibility layer that understands the quirks of each vendor and shields developers from them, any integration eventually degrades into a pile of conditional logic.

Synara’s value isn’t “simplifying invites.”
 It’s providing a single, consistent mental model for an ecosystem that fundamentally lacks one.