Documentation Index
Fetch the complete documentation index at: https://docs.agentfront.dev/llms.txt
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Overview
SDK errors cover a broad range of internal failures across the FrontMCP SDK — flow execution, server configuration, skill management, serverless handlers, Vercel KV, and more. Most are internal errors except MissingPromptArgumentError (documented under Validation Errors).
Flow Errors
FlowExitedWithoutOutputError
Thrown when a flow completes all stages without producing output.
| Property | Type | Value |
|---|
code | string | FLOW_EXITED_WITHOUT_OUTPUT |
statusCode | number | 500 |
isPublic | boolean | false |
new FlowExitedWithoutOutputError()
Thrown when a flow stage receives missing or undefined input.
| Property | Type | Value |
|---|
code | string | FLOW_INPUT_MISSING |
statusCode | number | 500 |
isPublic | boolean | false |
field | string | The missing field name |
flowName | string | undefined | The flow that encountered the error |
new FlowInputMissingError(field: string, flowName?: string)
import { FlowInputMissingError } from '@frontmcp/sdk';
throw new FlowInputMissingError('request', 'well-known.oauth');
// "Flow "well-known.oauth" is missing required input: "request""
Server & Configuration Errors
ServerNotFoundError
Thrown when no MCP server is found.
| Property | Type | Value |
|---|
code | string | SERVER_NOT_FOUND |
statusCode | number | 500 |
isPublic | boolean | false |
new ServerNotFoundError()
ConfigNotFoundError
Thrown when a configuration file is not found at the expected path.
| Property | Type | Value |
|---|
code | string | CONFIG_NOT_FOUND |
statusCode | number | 500 |
isPublic | boolean | false |
new ConfigNotFoundError(path: string, triedPaths?: string[])
import { ConfigNotFoundError } from '@frontmcp/sdk';
throw new ConfigNotFoundError('frontmcp.config.ts', ['./frontmcp.config.ts', './config/frontmcp.ts']);
ScopeConfigurationError
Thrown when the scope configuration is invalid.
| Property | Type | Value |
|---|
code | string | SCOPE_CONFIGURATION_ERROR |
statusCode | number | 500 |
isPublic | boolean | false |
new ScopeConfigurationError(message: string)
RequiredConfigUndefinedError
Thrown when a required configuration value is undefined.
| Property | Type | Value |
|---|
code | string | REQUIRED_CONFIG_UNDEFINED |
statusCode | number | 500 |
isPublic | boolean | false |
new RequiredConfigUndefinedError(path: string)
import { RequiredConfigUndefinedError } from '@frontmcp/sdk';
throw new RequiredConfigUndefinedError('auth.secret');
// "Required configuration path "auth.secret" is undefined"
Session & Auth Errors
SessionVerificationFailedError
Thrown when session verification fails.
| Property | Type | Value |
|---|
code | string | SESSION_VERIFICATION_FAILED |
statusCode | number | 500 |
isPublic | boolean | false |
new SessionVerificationFailedError()
Context Errors
ContextExtensionNotAvailableError
Thrown when a context extension (e.g., this.remember) is not available, typically because the required plugin is not installed.
| Property | Type | Value |
|---|
code | string | CONTEXT_EXTENSION_NOT_AVAILABLE |
statusCode | number | 500 |
isPublic | boolean | false |
originalError | Error | undefined | The underlying cause |
new ContextExtensionNotAvailableError(message: string, cause?: Error)
InvokeStateMissingKeyError
Thrown when an invoke state key is missing during flow execution.
| Property | Type | Value |
|---|
code | string | INVOKE_STATE_MISSING_KEY |
statusCode | number | 500 |
isPublic | boolean | false |
new InvokeStateMissingKeyError(key: string)
Skill Errors
SkillSessionError
Thrown when a skill session operation fails.
| Property | Type | Value |
|---|
code | string | SKILL_SESSION_ERROR |
statusCode | number | 500 |
isPublic | boolean | false |
new SkillSessionError(operation: string, reason: string)
InvalidSkillError
Thrown when a skill definition is invalid.
| Property | Type | Value |
|---|
code | string | INVALID_SKILL |
statusCode | number | 500 |
isPublic | boolean | false |
new InvalidSkillError(name: string, details: string)
SkillInstructionFetchError
Thrown when fetching remote skill instructions fails.
| Property | Type | Value |
|---|
code | string | SKILL_INSTRUCTION_FETCH_FAILED |
statusCode | number | 500 |
isPublic | boolean | false |
new SkillInstructionFetchError(url: string, status: number, statusText: string)
InvalidInstructionSourceError
Thrown when an instruction source is invalid.
| Property | Type | Value |
|---|
code | string | INVALID_INSTRUCTION_SOURCE |
statusCode | number | 500 |
isPublic | boolean | false |
new InvalidInstructionSourceError()
Serverless Errors
ServerlessHandlerNotInitializedError
Thrown when a serverless handler is accessed before initialization.
| Property | Type | Value |
|---|
code | string | SERVERLESS_HANDLER_NOT_INITIALIZED |
statusCode | number | 500 |
isPublic | boolean | false |
new ServerlessHandlerNotInitializedError()
Adapter Errors
DynamicAdapterNameError
Thrown when a dynamic adapter has a name conflict.
| Property | Type | Value |
|---|
code | string | DYNAMIC_ADAPTER_NAME_ERROR |
statusCode | number | 500 |
isPublic | boolean | false |
new DynamicAdapterNameError(message: string)
Agent SDK Errors
AgentConfigKeyNotFoundError
Thrown when an agent configuration key is not found.
| Property | Type | Value |
|---|
code | string | AGENT_CONFIG_KEY_NOT_FOUND |
statusCode | number | 500 |
isPublic | boolean | false |
new AgentConfigKeyNotFoundError(path: string)
Thrown when an agent’s tool execution fails.
| Property | Type | Value |
|---|
code | string | AGENT_TOOL_EXECUTION_ERROR |
statusCode | number | 500 |
isPublic | boolean | false |
new AgentToolExecutionError(message: string)
AgentMethodNotAvailableError
Thrown when an agent method is not available.
| Property | Type | Value |
|---|
code | string | AGENT_METHOD_NOT_AVAILABLE |
statusCode | number | 500 |
isPublic | boolean | false |
new AgentMethodNotAvailableError(method: string, name: string)
Internal Utility Errors
DependencyNotFoundError
Thrown when a required dependency is not found in a registry during initialization.
| Property | Type | Value |
|---|
code | string | DEPENDENCY_NOT_FOUND |
statusCode | number | 500 |
isPublic | boolean | false |
new DependencyNotFoundError(registryName: string, dependencyName: string)
import { DependencyNotFoundError } from '@frontmcp/sdk';
throw new DependencyNotFoundError('AuthRegistry', 'SessionStore');
// "Dependency "SessionStore" not found in AuthRegistry"
GenericServerError
A general-purpose internal error wrapper. Used by toMcpError() to wrap unknown errors.
| Property | Type | Value |
|---|
code | string | SERVER_ERROR |
statusCode | number | 500 |
isPublic | boolean | false |
originalError | Error | undefined | The underlying cause |
new GenericServerError(message: string, originalError?: Error)
GlobalConfigNotFoundError
Thrown when a plugin requires global configuration that is not defined in the @FrontMcp decorator.
| Property | Type | Value |
|---|
code | string | GLOBAL_CONFIG_NOT_FOUND |
statusCode | number | 500 |
isPublic | boolean | true |
pluginName | string | The plugin that requires config |
configKey | string | The missing config key |
new GlobalConfigNotFoundError(pluginName: string, configKey: string)
import { GlobalConfigNotFoundError } from '@frontmcp/sdk';
throw new GlobalConfigNotFoundError('RememberPlugin', 'redis');
// 'Plugin "RememberPlugin" requires global "redis" configuration. Add "redis" to your @FrontMcp decorator options.'
RequestContextNotAvailableError
Thrown when code attempts to access RequestContext outside a request scope (without AsyncLocalStorage context).
| Property | Type | Value |
|---|
code | string | REQUEST_CONTEXT_NOT_AVAILABLE |
statusCode | number | 500 |
isPublic | boolean | false |
new RequestContextNotAvailableError(message?: string)
Vercel KV Errors
VercelKvNotSupportedError
Thrown when Vercel KV does not support a requested feature.
| Property | Type | Value |
|---|
code | string | VERCEL_KV_NOT_SUPPORTED |
statusCode | number | 500 |
isPublic | boolean | false |
new VercelKvNotSupportedError(feature: string)
VercelKvAsyncInitRequiredError
Thrown when Vercel KV is used before async initialization.
| Property | Type | Value |
|---|
code | string | VERCEL_KV_ASYNC_INIT_REQUIRED |
statusCode | number | 500 |
isPublic | boolean | false |
new VercelKvAsyncInitRequiredError(message?: string)
