SDK Errors

General SDK errors for flows, configuration, skills, serverless, and runtime issues.

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)