> ## Documentation Index
> Fetch the complete documentation index at: https://docs.zeroruntime.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Errors & Enums
> Python API reference for Errors & Enums.
Shared configuration and state types: session and user state enums, speech and VAD
event types, and the config objects for end-of-utterance, interruption, and
realtime behavior.
## ZeroRuntimeError
Base for everything this SDK raises on its own behalf.
Catch it to handle any ZeroRuntime failure without naming each one. Errors
the standard library raises -- `ValueError` for a bad argument,
`TimeoutError` for a request that went unanswered -- are left as
themselves rather than wrapped.
***
## SessionRejected
The ZeroRuntime refused to create the session.
### Constructor
```python theme={null}
SessionRejected(message: 'str' = '', *, code: 'str' = '', current_sessions: 'int' = 0, max_sessions: 'int' = 0) -> 'None'
```
The ZeroRuntime's explanation.
Machine-readable reason, `at_capacity` | `invalid_config` | `internal`. `at_capacity` is worth retrying elsewhere; `invalid_config` never is.
Sessions the ZeroRuntime is already running.
The ZeroRuntime's ceiling, when it reported one.
***
## ProviderUnavailable
A provider in the pipeline could not be reached or would not serve.
Usually a missing or rejected vendor key, or a model the account is not
entitled to. A fallback on the same slot is what keeps this from ending the
call.
***
## ZeroRuntimeUnreachable
The runtime could not be reached, or did not answer in time.
A transport failure rather than a refusal: nothing was decided about the
session, so retrying is reasonable.
***
## ToolTimeout
A `@function_tool` did not return before its deadline.
The turn continues without the tool's answer. A tool that calls out to a
slow API wants its own timeout, so it can say something useful instead of
being cut off.
***
## AgentState
Where the agent is in a turn -- listening, thinking, speaking, or on its
way in or out of the call.
```python theme={null}
class AgentState(Enum):
STARTING = 'starting'
IDLE = 'idle'
SPEAKING = 'speaking'
LISTENING = 'listening'
THINKING = 'thinking'
CLOSING = 'closing'
```
***
## UserState
What the caller is doing, as the runtime reports it.
```python theme={null}
class UserState(Enum):
IDLE = 'idle'
SPEAKING = 'speaking'
LISTENING = 'listening'
```
***
## ChatRole
Who a message in the conversation came from.
A plain string works anywhere one of these is accepted -- it subclasses
`str` -- so `"user"` and `ChatRole.USER` are interchangeable.
```python theme={null}
class ChatRole(Enum):
SYSTEM = 'system'
USER = 'user'
ASSISTANT = 'assistant'
DEVELOPER = 'developer'
TOOL = 'tool'
```