Crate fastmcp_protocol

Expand description

MCP protocol types and JSON-RPC implementation.

This crate provides:

JSON-RPC 2.0 message types
MCP-specific method types (tools, resources, prompts)
Protocol version negotiation
Message serialization/deserialization

MCP 2026-07-28 support is under implementation and remains unverified. Its core vocabulary is always available. Optional legacy, Tasks, and Apps wire surfaces require their matching crate features and are not aggregate conformance or release evidence.

§MCP Protocol Overview

MCP (Model Context Protocol) uses JSON-RPC 2.0 over various transports. The protocol defines:

Tools: Executable functions the client can invoke
Resources: Data sources the client can read
Prompts: Template prompts for the client to use

§Wire Format

Protocol values serialize as JSON-RPC. Framing is transport-specific; the stdio transport uses newline-delimited JSON (NDJSON).

§Role in the System

fastmcp-protocol is the shared vocabulary for FastMCP:

The server uses these types to validate and serialize responses.
The client uses the same types to construct requests and parse replies.
Transports carry these messages without needing to know business logic.

If you are integrating FastMCP with a custom runtime or embedding it into another system, depend on this crate to use FastMCP’s current JSON-RPC and MCP data models. The modernization disclaimer above still applies.

Re-exports§

pub use common_types::JsonInteger;
pub use extensions::ClientExtensionDiscovery;
pub use extensions::ExtensionDescriptor;
pub use extensions::ExtensionDescriptorRegistry;
pub use extensions::ExtensionDirection;
pub use extensions::ExtensionDiscovery;
pub use extensions::ExtensionFallbackPolicy;
pub use extensions::ExtensionHttpEraDisposition;
pub use extensions::ExtensionId;
pub use extensions::ExtensionMethodDescriptor;
pub use extensions::ExtensionNegotiationResolver;
pub use extensions::ExtensionNotificationDescriptor;
pub use extensions::ExtensionRegistryError;
pub use extensions::ExtensionRegistryReceipt;
pub use extensions::ExtensionRoutingHeaderDescriptor;
pub use extensions::ExtensionSettings;
pub use extensions::ExtensionSettingsCompatibilityResolver;
pub use extensions::ExtensionSettingsResolution;
pub use extensions::ExtensionSettingsSchema;
pub use extensions::MAX_EXTENSION_DESCRIPTORS;
pub use extensions::MAX_EXTENSION_ID_BYTES;
pub use extensions::MAX_EXTENSION_REGISTRY_CANONICAL_BYTES;
pub use extensions::MAX_EXTENSION_SETTINGS_ENTRIES;
pub use extensions::MAX_EXTENSION_SETTINGS_KEY_BYTES;
pub use extensions::MAX_EXTENSION_SETTINGS_NESTING;
pub use extensions::MAX_EXTENSION_SETTINGS_VALUE_BYTES;
pub use extensions::MAX_MCP_APPS_MIME_TYPE_BYTES;
pub use extensions::MAX_MCP_APPS_MIME_TYPES;
pub use extensions::MCP_APPS_ACTIVATION_PREDICATE_ID;
pub use extensions::MCP_APPS_CLIENT_SETTINGS_SCHEMA_ID;
pub use extensions::MCP_APPS_DOWNLOAD_FILE_METHOD;
pub use extensions::MCP_APPS_HOST_CONTEXT_CHANGED_NOTIFICATION;
pub use extensions::MCP_APPS_HTML_MIME_TYPE;
pub use extensions::MCP_APPS_INITIALIZE_METHOD;
pub use extensions::MCP_APPS_INITIALIZED_NOTIFICATION;
pub use extensions::MCP_APPS_MESSAGE_METHOD;
pub use extensions::MCP_APPS_NEGOTIATION_RESOLVER_ID;
pub use extensions::MCP_APPS_OPEN_LINK_METHOD;
pub use extensions::MCP_APPS_REQUEST_DISPLAY_MODE_METHOD;
pub use extensions::MCP_APPS_REQUEST_TEARDOWN_NOTIFICATION;
pub use extensions::MCP_APPS_RESOURCE_TEARDOWN_METHOD;
pub use extensions::MCP_APPS_SANDBOX_PROXY_READY_NOTIFICATION;
pub use extensions::MCP_APPS_SANDBOX_RESOURCE_READY_NOTIFICATION;
pub use extensions::MCP_APPS_SERVER_SETTINGS_SCHEMA_ID;
pub use extensions::MCP_APPS_SIZE_CHANGED_NOTIFICATION;
pub use extensions::MCP_APPS_TOOL_CANCELLED_NOTIFICATION;
pub use extensions::MCP_APPS_TOOL_INPUT_NOTIFICATION;
pub use extensions::MCP_APPS_TOOL_INPUT_PARTIAL_NOTIFICATION;
pub use extensions::MCP_APPS_TOOL_RESULT_NOTIFICATION;
pub use extensions::MCP_APPS_UPDATE_MODEL_CONTEXT_METHOD;
pub use extensions::McpAppsClientSettings;
pub use extensions::McpAppsNegotiationResolver;
pub use extensions::OFFICIAL_MCP_APPS_EXTENSION_ID;
pub use extensions::RejectingExtensionNegotiationResolver;
pub use extensions::ServerExtensionDiscovery;
pub use extensions::StdioCorrelationDescriptor;
pub use extensions::official_mcp_apps_descriptor;
pub use extensions::official_mcp_apps_empty_server_settings;
pub use extensions::official_mcp_apps_extension_id;
pub use extensions::official_mcp_apps_negotiation_resolver;
pub use extensions::register_official_mcp_apps_extension;
pub use extensions::resolve_official_mcp_apps_settings;
pub use methods::SERVER_DISCOVER;
pub use protocol_version::FINAL_PROTOCOL_VERSION;
pub use protocol_version::FinalHttpRequestMetadata;
pub use protocol_version::FinalProtocolVersion;
pub use protocol_version::FinalRequestAdmission;
pub use protocol_version::HEADER_MISMATCH_ERROR_CODE;
pub use protocol_version::HeaderMismatchError;
pub use protocol_version::HeaderMismatchReason;
pub use protocol_version::MAX_REQUIRED_CAPABILITIES_ERROR_DATA_BYTES;
pub use protocol_version::MCP_METHOD_HEADER;
pub use protocol_version::MCP_NAME_HEADER;
pub use protocol_version::MCP_PROTOCOL_VERSION_HEADER;
pub use protocol_version::MISSING_REQUIRED_CLIENT_CAPABILITY_ERROR_CODE;
pub use protocol_version::MissingRequiredClientCapabilityError;
pub use protocol_version::ProtocolVersionError;
pub use protocol_version::RequestAdmissionError;
pub use protocol_version::RequestVersionMetadata;
pub use protocol_version::RequiredCapabilitiesError;
pub use protocol_version::SUPPORTED_FINAL_PROTOCOL_VERSIONS;
pub use protocol_version::UNSUPPORTED_PROTOCOL_VERSION_ERROR_CODE;
pub use protocol_version::UnsupportedProtocolVersionError;
pub use protocol_version::admit_final_http_request;
pub use protocol_version::admit_final_request;
pub use protocol_version::validate_final_protocol_version;
pub use schema::AdmittedFinalFormSchema;
pub use schema::AdmittedSchema;
pub use schema::FinalCoreResultType;
pub use schema::SchemaAdmissionError;
pub use schema::ValidationError;
pub use schema::ValidationResult;
pub use schema::admit_final_form_schema;
pub use schema::admit_final_schema;
pub use schema::validate;
pub use schema::validate_final_core_result;
pub use schema::validate_strict;
pub use server_discovery::DiscoveryCacheHints;
pub use server_discovery::MAX_SERVER_INSTRUCTIONS_BYTES;
pub use server_discovery::SERVER_DISCOVER_METHOD;
pub use server_discovery::SERVER_DISCOVER_SERVER_INFO_META_KEY;
pub use server_discovery::SERVER_DISCOVER_SUPPORTED_VERSIONS;
pub use server_discovery::ServerBehavior;
pub use server_discovery::ServerBehaviorRegistry;
pub use server_discovery::ServerDiscoverCapabilities;
pub use server_discovery::ServerDiscoverRequest;
pub use server_discovery::ServerDiscoverResult;
pub use server_discovery::ServerDiscoveryError;
pub use server_discovery::ServerInstructionError;
pub use server_discovery::ServerInstructions;
pub use uri_template::MAX_URI_TEMPLATE_BYTES;
pub use uri_template::MAX_URI_TEMPLATE_COMPOSITE_ITEMS;
pub use uri_template::MAX_URI_TEMPLATE_EXPANSION_OUTPUT_BYTES;
pub use uri_template::MAX_URI_TEMPLATE_EXPRESSIONS;
pub use uri_template::MAX_URI_TEMPLATE_PARTS;
pub use uri_template::MAX_URI_TEMPLATE_PREFIX_LENGTH;
pub use uri_template::MAX_URI_TEMPLATE_VALUE_BYTES;
pub use uri_template::MAX_URI_TEMPLATE_VARIABLE_NAME_BYTES;
pub use uri_template::MAX_URI_TEMPLATE_VARIABLES_PER_EXPRESSION;
pub use uri_template::ReversibleResourceTemplate;
pub use uri_template::TemplateValue;
pub use uri_template::TemplateValues;
pub use uri_template::UriTemplate;
pub use uri_template::UriTemplateError;
pub use uri_template::UriTemplateExpansionLimits;
pub use uri_template::UriTemplateExpression;
pub use uri_template::UriTemplateModifier;
pub use uri_template::UriTemplateOperator;
pub use uri_template::UriTemplatePart;

Modules§

common_types: Final MCP common wire types kept separate while the legacy type surface is migrated.
extensions: Frozen, runtime-neutral extension negotiation and request admission.
methods: Canonical MCP JSON-RPC method names.
protocol_policy: Exact MCP protocol-version identity and immutable era-policy selection.
protocol_version: Final MCP protocol-version header validation.
schema: JSON Schema validation for MCP tool inputs.
server_discovery: Typed server/discover vocabulary for the final MCP discovery surface.
uri_template: Bounded RFC 6570 Level 4 URI-template parsing and expansion.

Structs§

CacheTtl: A nonnegative final cache TTL that retains its exact JSON-integer spelling.
CacheableResult: A complete-result composition with strict cache hints.
CallToolParams: tools/call request params.
CallToolResult: tools/call response result.
CancelledParams: Cancelled notification params.
ClientCapabilities: Client capabilities.
ClientInfo: Client information.
CompleteResult: A typed core complete result with inert open siblings.
CompletionValues: Completion candidates returned by the legacy protocol era.
CompletionsCapability: Empty object advertised when completion/complete is installed.
CoreResultDiscriminatorPolicy: The default policy: only core discriminators are accepted locally.
CreateMessageParams: sampling/createMessage request params.
CreateMessageResult: sampling/createMessage response result.
ElicitCompleteNotificationParams: Elicitation complete notification params.
ElicitRequestFormParams: Parameters for form mode elicitation requests.
ElicitRequestUrlParams: Parameters for URL mode elicitation requests.
ElicitResult: elicitation/create response result.
ElicitationCapability: Elicitation capability.
ElicitationRequiredErrorData: Error data for URL elicitation required errors.
ExactJsonMember: One JSON object member.
ExactJsonObject: An ordered JSON object.
FinalBaseMetadata: Shared final component identity fields.
FinalCallToolParams: Final tools/call request parameters.
FinalCallToolResult: Final tools/call result payload using final common content blocks.
FinalCancelledNotificationParams: Exact final notifications/cancelled parameters.
FinalCompletionArgument: Final completion argument selector.
FinalCompletionContext: Optional final completion context.
FinalCompletionParams: Final completion/complete request parameters.
FinalCompletionResult: Final completion/complete result payload.
FinalCompletionValues: Completion candidates returned by the final protocol era.
FinalCreateMessageInputRequiredResult: Exact final sampling/createMessage input-required result.
FinalCreateMessageParams: Exact final sampling/createMessage parameters.
FinalCreateMessageResult: Exact final sampling/createMessage complete payload.
FinalEmbeddedCreateMessageParams: Exact final parameters for an embedded sampling descriptor.
FinalEmbeddedElicitationResult: Exact elicitation response payload embedded in a Task input response map.
FinalEmbeddedFormElicitationParams: Form elicitation request parameters without an outer request envelope.
FinalEmbeddedRootsListParams: Bounded generic metadata permitted on an embedded roots descriptor.
FinalEmbeddedRootsListResult: Exact roots-list result payload embedded in a Task input response map.
FinalEmbeddedUrlElicitationParams: URL elicitation request parameters without legacy elicitation identity.
FinalEmptyNotificationParams: Exact optional parameter object for final catalog-change notifications.
FinalEmptyParams: Final empty request parameters, used by server/discover.
FinalEmptyResult: Empty final complete-result payload used by acknowledgement methods.
FinalGetPromptParams: Final prompts/get request parameters.
FinalGetPromptResult: Final prompts/get result payload.
FinalInputResponses: Typed, order-preserving client replies to server-issued final MRTR input requests.
FinalListParams: Final pagination parameters shared by the core catalog methods.
FinalListPromptsResult: Final prompts/list result payload.
FinalListResourceTemplatesResult: Final resources/templates/list result payload.
FinalListResourcesResult: Final resources/list result payload.
FinalListToolsResult: Final tools/list result payload.
FinalLogMessageParams: Exact final notifications/message parameters.
FinalProgressNotificationParams: Exact final notifications/progress parameters.
FinalPrompt: Exact final Prompt model.
FinalPromptArgument: Exact final prompt-argument model.
FinalPromptMessage: One final prompt message using a final common content block.
FinalReadResourceParams: Final resources/read request parameters.
FinalReadResourceResult: Final resources/read result payload using final common resource content.
FinalRequestMeta: Required final metadata carried in the _meta object of every request.
FinalResource: Exact final Resource model.
FinalResourceTemplate: Exact final ResourceTemplate model.
FinalResourceUpdatedNotificationParams: Exact final notifications/resources/updated parameters.
FinalResultMetadataSeal: Server-owned final metadata retained across response middleware.
FinalSamplingMessage: A final sampling conversation message.
FinalSubscriptionsAcknowledgedNotificationParams: Final notifications/subscriptions/acknowledged parameters.
FinalSubscriptionsListenParams: Final subscriptions/listen request parameters.
FinalSubscriptionsListenResult: Empty final subscriptions/listen result body.
FinalTool: Exact final Tool model.
FinalToolAnnotations: Final tool annotations, including the final display-title hint.
FinalToolChoice: Tool-selection controls for final sampling.
FormElicitationCapability: Capability for form mode elicitation.
GetPromptParams: prompts/get request params.
GetPromptResult: prompts/get response result.
Icon: Icon metadata for visual representation of components.
InitializeParams: Initialize request params.
InitializeResult: Initialize response result.
InputRequiredResult: A typed core input_required result with inert open siblings.
JsonRpcError: JSON-RPC 2.0 error object.
JsonRpcRequest: JSON-RPC 2.0 request.
JsonRpcResponse: JSON-RPC 2.0 response.
JsonRpcResponseAdmission: One strictly admitted JSON-RPC response paired with the exact source JSON of its result member.
LegacyCompletionArgument: Exact legacy completion argument selector.
LegacyCompletionParams: Exact 2024-11-05 completion/complete request parameters.
LegacyCompletionResult: Exact legacy completion/complete result payload.
LegacyEmptyResult: Empty exact-legacy result payload used by acknowledgement methods.
LegacyOpaqueMetadata: Ordered opaque legacy metadata.
LegacyPromptMessage: Exact 2024-11-05 prompt messages carried in legacy results.
ListPromptsParams: prompts/list request params.
ListPromptsResult: prompts/list response result.
ListResourceTemplatesParams: resources/templates/list request params.
ListResourceTemplatesResult: resources/templates/list response result.
ListResourcesParams: resources/list request params.
ListResourcesResult: resources/list response result.
ListRootsParams: roots/list request params.
ListRootsResult: roots/list response result.
ListToolsParams: tools/list request params.
ListToolsResult: tools/list response result.
LogMessageParams: Log message notification params.
LoggingCapability: Logging capability.
McpAppsResourceBinding: A validated association between a tool’s nested Apps metadata and an HTML UI resource in the final catalog.
McpAppsResourceCsp: Bounded CSP origins declared by an Apps resource.
McpAppsResourceMetadata: Closed Apps rendering metadata attached to a Resource under _meta.ui.
McpAppsResourcePermission: An empty-object Apps sandbox permission marker.
McpAppsResourcePermissions: Optional sandbox permissions requested by an Apps resource.
McpAppsToolMetadata: Closed Apps metadata attached to a final Tool under _meta.ui.
McpAppsToolResult: One validated Apps-side projection of a complete final tools/call result.
MetadataView: Read-only view of optional result metadata.
ModelHint: A hint for model selection.
ModelPreferences: Model preferences for sampling requests.
PaginatedResult: A complete-result composition with a pagination cursor.
ProgressParams: Progress notification params.
Prompt: Prompt definition.
PromptArgument: Prompt argument definition.
PromptMessage: A message in a prompt.
PromptsCapability: Prompt capabilities.
RawResultEnvelope: A raw result envelope for a non-core discriminator. It is diagnostic data, not an activated extension result.
ReadResourceParams: resources/read request params.
ReadResourceResult: resources/read response result.
RequestMeta: Request metadata containing optional progress marker.
Resource: Resource definition.
ResourceContent: Resource content in a message.
ResourceTemplate: Resource template definition.
ResourceUpdatedNotificationParams: Resource updated notification params.
ResourcesCapability: Resource capabilities.
ResultDecodeError: An error raised while admitting or decoding a result envelope.
ResultMeta: Result metadata common to complete and input-required results.
Root: A root definition representing a filesystem location.
RootsCapability: Roots capability.
RootsListChangedNotificationParams: Notification params for roots/list_changed.
SamplingCapability: Sampling capability.
SamplingMessage: A message in a sampling conversation.
ServerCapabilities: Server capabilities advertised during initialization.
ServerInfo: Server information.
SetLogLevelParams: logging/setLevel request params.
SubscribeResourceParams: resources/subscribe request params.
SubscriptionFilter: Final notification categories selected for a subscription stream.
TaskId: Task identifier.
TaskInfo: Information about a background task.
TaskResult: Task result payload.
TaskStatusNotificationParams: Task status change notification params.
TasksCapability: Task capability for server capabilities.
Tool: Tool definition.
ToolAnnotations: Tool annotations for additional metadata.
ToolsCapability: Tool capabilities.
TypedCompleteMembers: Guarded access to one selected complete composition’s declared members.
UncorrelatedJsonRpcErrorResponse: An error response that is deliberately uncorrelated and omits id.
UnknownResultMembers: Bounded, inert open members retained after known-field consumption.
UnsubscribeResourceParams: resources/unsubscribe request params.
UrlElicitationCapability: Capability for URL mode elicitation.

Enums§

CacheScope: Peer cache scope. Public is a wire value, not an authority grant.
CacheTtlConversionError: Failure while validating or converting a final cache TTL.
CancellationSender: Peer that originates a cancellation notification.
CancellationWireCodecError: Stable refusal classes for CancellationWireMessage codec operations.
CancellationWireMessage: An era-selected notifications/cancelled JSON-RPC notification.
ClientIngressFailureScope: Transport ownership for a client-ingress raw protocol failure.
ClientNotification: The one notification a final client may originate.
Content: Content types used by the broader server and 2026 adapter surfaces.
CoreDispatchError: Stable errors raised while selecting a typed core request or result.
CoreRequest: Public, era-aware dispatch for the currently supported core request set.
CoreResult: Public, era-aware dispatch for core results.
CorrelationKey: Canonical map/registry key for a JSON-RPC request ID.
DecodedResult: Core or deferred result decoded from a peer envelope.
ElicitAction: User action in response to an elicitation request.
ElicitContentValue: Content type for elicitation responses.
ElicitMode: Elicitation mode.
ElicitRequestParams: Parameters for elicitation requests (either form or URL mode).
ExactJsonValue: A recursively bounded JSON value which preserves each number’s source lexeme. This is the result codec’s exact-value boundary; it never uses an f64 or a fixed-width integer for an admitted JSON number.
FinalArguments: Wire presence of an optional final request arguments member.
FinalCompletionPeerDiagnostic: Bounded peer conformance diagnostics specific to final completion values.
FinalCompletionReference: Final reference accepted by completion/complete.
FinalCoreRequest: Final core requests use final metadata and common vocabulary throughout.
FinalCoreResult: Final result dispatch for the currently supported core methods.
FinalEmbeddedElicitationParams: Exact final parameters for an embedded elicitation descriptor.
FinalEmbeddedInputKind: The selected final MRTR response kind for one Task map key.
FinalEmbeddedInputRequest: A final MRTR descriptor embedded in a Task, without a JSON-RPC envelope.
FinalEmbeddedInputResponse: A final MRTR result payload embedded in a Task, without a JSON-RPC envelope.
FinalInputRequiredResultType: Final input-required discriminator.
FinalInputResponseCorrelationError: Why a retry response map could not be correlated to a prior MRTR request.
FinalNotificationError: Typed admission error for an MCP 2026-07-28 notification union.
FinalSamplingMessageContent: Exact final sampling-message content, preserving one block versus an array of blocks.
FinalToolChoiceMode: Tool-selection mode for final sampling.
IncludeContext: Context inclusion mode for sampling.
JsonRpcAdmissionError: Admission failure for a complete strict JSON-RPC document.
JsonRpcEndpointRole: Immutable local endpoint role for raw JSON-RPC ingress disposition.
JsonRpcMessage: A JSON-RPC message (request, response, or notification).
JsonRpcMessageDirection: The direction attached by the local transport to a decoded message.
LegacyCompletionReference: Exact legacy reference accepted by completion/complete.
LegacyContent: Exact 2024-11-05 content blocks carried in legacy results.
LegacyCoreRequest: Legacy core requests remain exact uses of the existing message structs. They are never reinterpreted as final requests.
LegacyCoreResult: Exact legacy response payloads, intentionally disjoint from final results.
LegacyResourceContent: Exact 2024-11-05 resource contents carried by legacy results.
LogLevel: Log level.
McpAppsDisplayMode: A Host-selected way to present an App View.
McpAppsLifecycleError: Illegal transition in the pure Apps View lifecycle state machine.
McpAppsMetadataError: Metadata validation failures specific to the closed Apps ui member.
McpAppsResourceBindingError: A catalog resource did not satisfy one validated Apps binding.
McpAppsResultProjectionError: Apps result projection failures.
McpAppsToolVisibility: A tool audience declared in nested MCP Apps metadata.
McpAppsViewLifecycle: A View lifecycle phase. This pure protocol state machine does not send or receive any ui/* RPC message; a future bridge runtime owns that work.
ProgressMarker: Progress marker used to correlate progress notifications with requests.
RawJsonAdmissionError: A stable reason why raw JSON was rejected before typed decoding.
RawJsonRpcDisposition: Role-aware disposition of a raw malformed JSON-RPC document.
RequestId: JSON-RPC request ID.
ResultDecodeErrorKind: Stable result-decoding failure categories.
ResultDiscriminatorDecision: Result-discriminator decision made after raw structural admission.
ResultPeerDiagnostic: Bounded diagnostics reserved for peer-result compatibility handling.
ResultPeerEra: Protocol era used only for peer-ingress compatibility diagnostics.
Role: Role in prompt messages.
SamplingContent: Message content for sampling requests.
ServerNotification: The eight notifications a final server may originate.
StopReason: Stop reason for sampling responses.
TaskStatus: Status of a background task.

Constants§

FINAL_CLIENT_CAPABILITIES_META_KEY: _meta key carrying the client capabilities on every final request.
FINAL_CLIENT_INFO_META_KEY: _meta key carrying optional client identity on a final request.
FINAL_LOG_LEVEL_META_KEY: _meta key carrying the client-selected logging floor on a final request.
FINAL_PROTOCOL_VERSION_META_KEY: _meta key carrying the protocol version on every final request.
FINAL_SERVER_INFO_META_KEY: _meta key carrying optional server identity on a final response.
FINAL_SUBSCRIPTION_ID_META_KEY: _meta key correlating an event-stream subscription with its listen request.
JSONRPC_VERSION: The JSON-RPC version string. Used as a static reference to avoid allocations.
MAX_CANCELLATION_REASON_BYTES: Historical cancellation-reason size used by earlier bounded profiles.
MAX_COMPLETION_CONTEXT_ARGUMENTS: Maximum number of previously resolved variables in one final completion context.
MAX_COMPLETION_CONTEXT_ARGUMENT_BYTES: Maximum encoded JSON bytes occupied by one final completion-context argument map.
MAX_COMPLETION_CONTEXT_ARGUMENT_KEY_BYTES: Maximum UTF-8 bytes in one final completion-context variable name.
MAX_COMPLETION_CONTEXT_ARGUMENT_VALUE_BYTES: Maximum UTF-8 bytes in one final completion-context variable value.
MAX_COMPLETION_VALUES: Maximum completion candidates allowed on the wire by either supported era.
MAX_FINAL_COMPLETION_VALUES_BYTES: Maximum aggregate UTF-8 bytes in final completion candidates.
MAX_FINAL_COMPLETION_VALUE_BYTES: Maximum UTF-8 bytes in one final completion candidate.
MAX_JSONRPC_STRING_ID_ENCODED_BYTES: Maximum encoded bytes in one JSON-RPC string ID, including quotes.
MAX_MCP_APPS_CSP_DOMAINS_PER_DIRECTIVE: Maximum origins retained by one Apps CSP directive.
MAX_MCP_APPS_CSP_DOMAIN_BYTES: Maximum UTF-8 bytes retained for one Apps CSP origin or host-selected domain.
MAX_MCP_APPS_TOOL_VISIBILITY_ENTRIES: Maximum audience entries retained by one Apps tool visibility declaration.
MAX_MCP_APPS_UI_METADATA_MEMBERS: Maximum members in a closed nested MCP Apps tool ui metadata object.
MAX_RAW_JSON_AGGREGATE_NUMBER_BYTES: Maximum aggregate encoded number bytes in one admitted JSON document.
MAX_RAW_JSON_CONTAINER_ENTRIES: Default maximum aggregate object members and array elements for raw JSON admission.
MAX_RAW_JSON_EXPONENT: Maximum absolute decimal exponent accepted by raw JSON admission.
MAX_RAW_JSON_NESTING_DEPTH: Default maximum nesting depth for raw JSON admission.
MAX_RAW_JSON_NUMBER_BYTES: Maximum encoded bytes in one JSON number token before typed decoding.
MAX_RESULT_CONTAINER_MEMBERS: Maximum members/elements accepted by one JSON object or array.
MAX_RESULT_DEPTH: Maximum nesting depth accepted by the result codec.
MAX_RESULT_ENCODED_BYTES: Maximum encoded bytes accepted by the result codec.
MAX_RESULT_NUMBER_BYTES: Maximum source bytes in one JSON number lexeme.
MAX_RESULT_STRING_BYTES: Maximum decoded bytes in one JSON string or object key.
MCP_APPS_DEPRECATED_RESOURCE_URI_METADATA_KEY: Deprecated flat metadata member that this final-only surface rejects.
MCP_APPS_UI_METADATA_KEY: Nested _meta member reserved by the MCP Apps protocol.
PROTOCOL_VERSION: MCP protocol version.

Traits§

CompleteResultPayload: Method-specific decoder for a selected core complete result composition.
ResultDiscriminatorPolicy: Registry-agnostic policy seam for already-admitted non-core result types. No policy in this module owns a descriptor registry or activates extensions.

Functions§

admit_raw_jsonrpc_document: Admit one complete raw JSON-RPC document before any typed decoding.
decode_peer_result: Decodes one peer result through the public result codec.
decode_peer_result_for_era: Decodes one peer result using the protocol era selected for its request.
decode_strict_jsonrpc_message: Decode a complete JSON-RPC message only after raw-document admission.
decode_strict_jsonrpc_response: Strictly decodes one JSON-RPC response while retaining its exact result member source for the final result algebra.
decode_typed_complete: Decodes a selected method-specific complete composition.
dispose_raw_jsonrpc_failure: Convert a raw admission failure into an endpoint-safe disposition.
encode_complete_result: Encodes one selected typed complete result through the final result algebra. Method dispatch supplies exactly the members it owns; every other admitted member remains an inert UnknownResultMembers sibling.
encode_result: Re-emits a result without discarding or semantically rewriting any retained open member. Safe complete and input-required variants always emit their explicit core discriminator.
exact_json_from_serde: Converts an ordinary serde value into the result algebra’s bounded exact representation before it is attached to a locally authored result.
exact_json_to_serde: Converts one exact result value into a serde value for a selected typed method payload. Open result siblings remain exact and are never converted unless that payload explicitly owns their member name.
parse_exact_json: Parses one bounded exact JSON value.
project_final_core_tools_call_result: Projects the complete tools/call branch while rejecting deferred Tasks and MRTR branches before any Apps result is produced.

Type Aliases§

ElicitRequestedSchema: JSON Schema for elicitation requests.
FinalSamplingMessageContentBlock: Final sampling-specific content block.
LegacyMetadata: Legacy 2024 metadata, retained exactly as an open JSON object.