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This page compares two ways Pinchtab can manage a browser instance:
- `managed + bridge`
- `managed + direct-cdp`
Both are **managed** because Pinchtab owns the instance lifecycle.
The difference is where the browser control logic lives and how the server reaches Chrome.
## Short Version
```text
managed + bridge
server -> bridge -> Chrome
managed + direct-cdp
server -> Chrome
```
The bridge model adds one extra process and one extra hop.
The direct-CDP model removes that hop and keeps control in the main server.
## Chart 1: Runtime Shape
```text
Managed + bridge
Pinchtab server
└─ Pinchtab bridge child
└─ Chrome
└─ Tabs
Managed + direct-cdp
Pinchtab server
└─ Chrome
└─ Tabs
```
## Managed + Bridge
### What it is
Pinchtab starts a child `pinchtab bridge` process for each managed instance.
That bridge owns one browser and exposes a single-instance HTTP API.
The main server routes instance and tab requests to that child.
### Communication Path
```text
agent -> server -> bridge -> Chrome
```
### Benefits
- strong per-instance isolation
- clearer process boundaries
- easier crash containment
- easier per-instance logs and health checks
- easier to reason about operationally as a worker model
### Costs
- one extra process per instance
- one extra HTTP hop before reaching Chrome
- more ports to allocate and monitor
- more startup overhead
- some configuration must be propagated to child runtimes
### Best fit
- multi-instance orchestration
- strong isolation between instances
- cases where instance failures should stay local
- systems that benefit from worker-style process supervision
## Managed + Direct-CDP
### What it is
Pinchtab starts Chrome itself and keeps the CDP session inside the main server process.
There is no bridge child and no extra per-instance HTTP server.
### Communication Path
```text
agent -> server -> Chrome
```
### Benefits
- fewer moving parts
- lower latency
- less process and port overhead
- simpler network model
- less duplicated HTTP handling
### Costs
- weaker process isolation by default
- more complexity inside the main server
- harder to contain instance-specific failures
- more shared memory and state inside one process
- main server becomes responsible for more lifecycle details directly
### Best fit
- low-overhead single-host deployments
- workloads where efficiency matters more than hard isolation
- environments where an extra worker process is unnecessary
- future architectures that want fewer internal hops
## Chart 2: Ownership And Transport
```text
managed + bridge
ownership: pinchtab
transport: http-bridge + cdp
managed + direct-cdp
ownership: pinchtab
transport: direct cdp
```
## Chart 3: Failure Boundary
```text
managed + bridge
one instance crash
-> bridge worker dies
-> instance is affected
-> server survives
managed + direct-cdp
one instance failure
-> handled inside server process
-> isolation depends on server design
```
## Decision Frame
Use this rule:
- choose **managed + bridge** when isolation and operational clarity matter more
- choose **managed + direct-cdp** when simplicity of the runtime path and lower overhead matter more
Or even shorter:
```text
bridge = better isolation
direct-cdp = better efficiency
```
## Current Status
Today, the intended architecture is:
- `managed + bridge` for Pinchtab-launched instances
- `attached + direct-cdp` for externally managed browsers
`managed + direct-cdp` is a useful future model, but it is primarily an architectural option, not the default implementation.
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