SDK Errors

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()

FlowInputMissingError

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)

Example:

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[])

Example:

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)

Example:

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)

AgentToolExecutionError

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)

Example:

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)

Example:

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)

Decorators

API

Errors

Overview

Flow Errors

FlowExitedWithoutOutputError

FlowInputMissingError

Server & Configuration Errors

ServerNotFoundError

ConfigNotFoundError

ScopeConfigurationError

RequiredConfigUndefinedError

Session & Auth Errors

SessionVerificationFailedError

Context Errors

ContextExtensionNotAvailableError

InvokeStateMissingKeyError

Skill Errors

SkillSessionError

InvalidSkillError

SkillInstructionFetchError

InvalidInstructionSourceError

Serverless Errors

ServerlessHandlerNotInitializedError

Adapter Errors

DynamicAdapterNameError

Agent SDK Errors

AgentConfigKeyNotFoundError

AgentToolExecutionError

AgentMethodNotAvailableError

Internal Utility Errors

DependencyNotFoundError

GenericServerError

GlobalConfigNotFoundError

RequestContextNotAvailableError

Vercel KV Errors

VercelKvNotSupportedError

VercelKvAsyncInitRequiredError

​Overview

​Flow Errors

​FlowExitedWithoutOutputError

​FlowInputMissingError

​Server & Configuration Errors

​ServerNotFoundError

​ConfigNotFoundError

​ScopeConfigurationError

​RequiredConfigUndefinedError

​Session & Auth Errors

​SessionVerificationFailedError

​Context Errors

​ContextExtensionNotAvailableError

​InvokeStateMissingKeyError

​Skill Errors

​SkillSessionError

​InvalidSkillError

​SkillInstructionFetchError

​InvalidInstructionSourceError

​Serverless Errors

​ServerlessHandlerNotInitializedError

​Adapter Errors

​DynamicAdapterNameError

​Agent SDK Errors

​AgentConfigKeyNotFoundError

​AgentToolExecutionError

​AgentMethodNotAvailableError

​Internal Utility Errors

​DependencyNotFoundError

​GenericServerError

​GlobalConfigNotFoundError

​RequestContextNotAvailableError

​Vercel KV Errors

​VercelKvNotSupportedError

​VercelKvAsyncInitRequiredError

Overview

Flow Errors

FlowExitedWithoutOutputError

FlowInputMissingError

Server & Configuration Errors

ServerNotFoundError

ConfigNotFoundError

ScopeConfigurationError

RequiredConfigUndefinedError

Session & Auth Errors

SessionVerificationFailedError

Context Errors

ContextExtensionNotAvailableError

InvokeStateMissingKeyError

Skill Errors

SkillSessionError

InvalidSkillError

SkillInstructionFetchError

InvalidInstructionSourceError

Serverless Errors

ServerlessHandlerNotInitializedError

Adapter Errors

DynamicAdapterNameError

Agent SDK Errors

AgentConfigKeyNotFoundError

AgentToolExecutionError

AgentMethodNotAvailableError

Internal Utility Errors

DependencyNotFoundError

GenericServerError

GlobalConfigNotFoundError

RequestContextNotAvailableError

Vercel KV Errors

VercelKvNotSupportedError

VercelKvAsyncInitRequiredError