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mcp: Deprecate roots, sampling and logging (SEP-2577) (#1017)

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Fixes #1013
This commit is contained in:
Guglielmo Colombo 2026-06-23 11:11:08 +02:00 • committed by GitHub
commit b6649db4f9
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13 changed files with 320 additions and 25 deletions
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2
mcp/capabilities_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (

47
mcp/client.go
View file

@ -82,6 +82,12 @@ type ClientOptions struct {
// &SamplingCapabilities{}. If [ClientOptions.Capabilities] is set and has a
// non nil value for [ClientCapabilities.Sampling], that value overrides the
// inferred capability.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). Migrate to calling LLM provider APIs
// directly from your server. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
CreateMessageHandler func(context.Context, *CreateMessageRequest) (*CreateMessageResult, error)
// CreateMessageWithToolsHandler handles incoming sampling/createMessage
// requests that may involve tool use. It returns
@ -95,6 +101,12 @@ type ClientOptions struct {
//
// It is a panic to set both CreateMessageHandler and
// CreateMessageWithToolsHandler.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). Migrate to calling LLM provider APIs
// directly from your server. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
CreateMessageWithToolsHandler func(context.Context, *CreateMessageWithToolsRequest) (*CreateMessageWithToolsResult, error)
// ElicitationHandler handles incoming requests for elicitation/create.
//
@ -152,10 +164,17 @@ type ClientOptions struct {
// ElicitationCompleteHandler handles incoming notifications for notifications/elicitation/complete.
ElicitationCompleteHandler func(context.Context, *ElicitationCompleteNotificationRequest)
// Handlers for notifications from the server.
ToolListChangedHandler func(context.Context, *ToolListChangedRequest)
PromptListChangedHandler func(context.Context, *PromptListChangedRequest)
ResourceListChangedHandler func(context.Context, *ResourceListChangedRequest)
ResourceUpdatedHandler func(context.Context, *ResourceUpdatedNotificationRequest)
ToolListChangedHandler func(context.Context, *ToolListChangedRequest)
PromptListChangedHandler func(context.Context, *PromptListChangedRequest)
ResourceListChangedHandler func(context.Context, *ResourceListChangedRequest)
ResourceUpdatedHandler func(context.Context, *ResourceUpdatedNotificationRequest)
// LoggingMessageHandler handles incoming notifications/message
// notifications from the server.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
LoggingMessageHandler func(context.Context, *LoggingMessageRequest)
ProgressNotificationHandler func(context.Context, *ProgressNotificationClientRequest)
// MultiRoundTrip configures the automatic MultiRoundTrip (Multi Round-Trip Requests) middleware.
@ -615,6 +634,12 @@ func (cs *ClientSession) startKeepalive(interval time.Duration) {
// AddRoots adds the given roots to the client,
// replacing any with the same URIs,
// and notifies any connected servers.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to passing paths via tool parameters,
// resource URIs, or configuration. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (c *Client) AddRoots(roots ...*Root) {
// Only notify if something could change.
if len(roots) == 0 {
@ -627,6 +652,12 @@ func (c *Client) AddRoots(roots ...*Root) {
// RemoveRoots removes the roots with the given URIs,
// and notifies any connected servers if the list has changed.
// It is not an error to remove a nonexistent root.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to passing paths via tool parameters,
// resource URIs, or configuration. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (c *Client) RemoveRoots(uris ...string) {
changeAndNotify(c, notificationRootsListChanged, &RootsListChangedParams{},
func() bool { return c.roots.remove(uris...) })
@ -1242,6 +1273,14 @@ func (cs *ClientSession) CallTool(ctx context.Context, params *CallToolParams) (
return handleSend[*CallToolResult](ctx, methodCallTool, newClientRequest(cs, orZero[Params](params)))
}
// SetLoggingLevel sets the minimum severity level for log messages sent by
// the server.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to consuming stderr output (for STDIO
// servers) or OpenTelemetry. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (cs *ClientSession) SetLoggingLevel(ctx context.Context, params *SetLoggingLevelParams) error {
_, err := handleSend[*emptyResult](ctx, methodSetLevel, newClientRequest(cs, orZero[Params](params)))
return err

2
mcp/client_example_test.go
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@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 examples exercise deprecated SEP-2577 APIs (roots, sampling) for demonstration.
package mcp_test
import (

2
mcp/client_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (

10
mcp/content.go
View file

@ -189,6 +189,11 @@ func (c *EmbeddedResource) fromWire(wire *wireContent) {
// ToolUseContent represents a request from the assistant to invoke a tool.
// This content type is only valid in sampling messages.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ToolUseContent struct {
// ID is a unique identifier for this tool use, used to match with ToolResultContent.
ID string
@ -229,6 +234,11 @@ func (c *ToolUseContent) fromWire(wire *wireContent) {
// ToolResultContent represents the result of a tool invocation.
// This content type is only valid in sampling messages with role "user".
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ToolResultContent struct {
// ToolUseID references the ID from the corresponding ToolUseContent.
ToolUseID string

15
mcp/logging.go
View file

@ -69,6 +69,11 @@ func compareLevels(l1, l2 LoggingLevel) int {
}
// LoggingHandlerOptions are options for a LoggingHandler.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingHandlerOptions struct {
// The value for the "logger" field of logging notifications.
LoggerName string
@ -79,6 +84,11 @@ type LoggingHandlerOptions struct {
}
// A LoggingHandler is a [slog.Handler] for MCP.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingHandler struct {
opts LoggingHandlerOptions
ss *ServerSession
@ -101,6 +111,11 @@ func ensureLogger(l *slog.Logger) *slog.Logger {
// NewLoggingHandler creates a [LoggingHandler] that logs to the given [ServerSession] using a
// [slog.JSONHandler].
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func NewLoggingHandler(ss *ServerSession, opts *LoggingHandlerOptions) *LoggingHandler {
var buf bytes.Buffer
jsonHandler := slog.NewJSONHandler(&buf, &slog.HandlerOptions{

2
mcp/mcp_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (

2
mcp/mrtr_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by the license
// that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (

146
mcp/protocol.go
View file

@ -439,6 +439,11 @@ func (x *CancelledParams) GetProgressToken() any { return getProgressToken(x) }
func (x *CancelledParams) SetProgressToken(t any) { setProgressToken(x, t) }
// RootCapabilities describes a client's support for roots.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type RootCapabilities struct {
// ListChanged reports whether the client supports notifications for
// changes to the roots list.
@ -466,14 +471,27 @@ type ClientCapabilities struct {
// Deprecated: use RootsV2. As described in #607, Roots should have been a
// pointer to a RootCapabilities value. Roots will be continue to be
// populated, but any new fields will only be added in the RootsV2 field.
//
// The roots feature itself is also deprecated by SEP-2577; see RootsV2.
Roots struct {
// ListChanged reports whether the client supports notifications for
// changes to the roots list.
ListChanged bool `json:"listChanged,omitempty"`
} `json:"roots,omitempty"`
// RootsV2 is present if the client supports roots. When capabilities are explicitly configured via [ClientOptions.Capabilities]
// RootsV2 is present if the client supports roots. When capabilities are
// explicitly configured via [ClientOptions.Capabilities].
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
RootsV2 *RootCapabilities `json:"-"`
// Sampling is present if the client supports sampling from an LLM.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
Sampling *SamplingCapabilities `json:"sampling,omitempty"`
// Elicitation is present if the client supports elicitation from the server.
Elicitation *ElicitationCapabilities `json:"elicitation,omitempty"`
@ -641,6 +659,12 @@ type CompleteResult struct {
func (*CompleteResult) isResult() {}
// CreateMessageParams holds parameters for a sampling/createMessage request.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type CreateMessageParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -648,10 +672,11 @@ type CreateMessageParams struct {
// A request to include context from one or more MCP servers (including the
// caller), to be attached to the prompt. The client may ignore this request.
//
// The default is "none". Values "thisServer" and
// "allServers" are soft-deprecated. Servers SHOULD only use these values if
// the client declares ClientCapabilities.sampling.context. These values may
// be removed in future spec releases.
// The default is "none". The values "thisServer" and "allServers" are
// deprecated as of protocol version 2025-11-25 (SEP-2596) and will be
// removed no later than the sampling feature itself (SEP-2577). Servers
// SHOULD omit this field or use "none". See
// https://modelcontextprotocol.io/seps/2596-feature-lifecycle-and-deprecation-policy.
IncludeContext string `json:"includeContext,omitempty"`
// The maximum number of tokens to sample, as requested by the server. The
// client may choose to sample fewer tokens than requested.
@ -681,6 +706,11 @@ func (x *CreateMessageParams) SetProgressToken(t any) { setProgressToken(x, t) }
// and messages that support array content (for parallel tool calls).
//
// Use with [ServerSession.CreateMessageWithTools].
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type CreateMessageWithToolsParams struct {
Meta `json:"_meta,omitempty"`
IncludeContext string `json:"includeContext,omitempty"`
@ -741,6 +771,11 @@ func (p *CreateMessageWithToolsParams) toBase() (*CreateMessageParams, error) {
// object for compatibility with pre-2025-11-25 implementations. When
// unmarshaling, a single JSON content object is accepted and wrapped in a
// one-element slice.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingMessageV2 struct {
Content []Content `json:"content"`
Role Role `json:"role"`
@ -782,6 +817,11 @@ func (m *SamplingMessageV2) UnmarshalJSON(data []byte) error {
// The client should inform the user before returning the sampled message, to
// allow them to inspect the response (human in the loop) and decide whether to
// allow the server to see it.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type CreateMessageResult struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -828,6 +868,11 @@ func (r *CreateMessageResult) UnmarshalJSON(data []byte) error {
//
// When unmarshaling, a single JSON content object is accepted and wrapped in a
// one-element slice, for compatibility with clients that return a single block.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type CreateMessageWithToolsResult struct {
Meta `json:"_meta,omitempty"`
Content []Content `json:"content"`
@ -1218,6 +1263,12 @@ type ListResourcesResult struct {
func (x *ListResourcesResult) isResult() {}
func (x *ListResourcesResult) nextCursorPtr() *string { return &x.NextCursor }
// ListRootsParams holds parameters for a roots/list request.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ListRootsParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -1233,6 +1284,11 @@ func (x *ListRootsParams) SetProgressToken(t any) { setProgressToken(x, t) }
// The client's response to a roots/list request from the server. This result
// contains an array of Root objects, each representing a root directory or file
// that the server can operate on.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ListRootsResult struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -1277,8 +1333,20 @@ func (x *ListToolsResult) nextCursorPtr() *string { return &x.NextCursor }
//
// These map to syslog message severities, as specified in RFC-5424:
// https://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingLevel string
// LoggingMessageParams holds the parameters for a notifications/message
// notification.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingMessageParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -1301,6 +1369,11 @@ func (x *LoggingMessageParams) SetProgressToken(t any) { setProgressToken(x, t)
//
// Keys not declared here are currently left unspecified by the spec and are up
// to the client to interpret.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ModelHint struct {
// A hint for a model name.
//
@ -1327,6 +1400,11 @@ type ModelHint struct {
// These preferences are always advisory. The client may ignore them. It is also
// up to the client to decide how to interpret these preferences and how to
// balance them against other considerations.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ModelPreferences struct {
// How much to prioritize cost when selecting a model. A value of 0 means cost
// is not important, while a value of 1 means cost is the most important factor.
@ -1652,6 +1730,11 @@ type ResourceTemplate struct {
type Role string
// Represents a root directory or file that the server can operate on.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type Root struct {
// See [specification/2025-06-18/basic/index#general-fields] for notes on _meta
// usage.
@ -1666,6 +1749,13 @@ type Root struct {
URI string `json:"uri"`
}
// RootsListChangedParams holds parameters for a notifications/roots/list_changed
// notification.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type RootsListChangedParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -1681,6 +1771,11 @@ func (x *RootsListChangedParams) SetProgressToken(t any) { setProgressToken(x, t
// below directly above ClientCapabilities.
// SamplingCapabilities describes the client's support for sampling.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingCapabilities struct {
// Context indicates the client supports includeContext values other than "none".
Context *SamplingContextCapabilities `json:"context,omitempty"`
@ -1689,12 +1784,27 @@ type SamplingCapabilities struct {
}
// SamplingContextCapabilities indicates the client supports context inclusion.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingContextCapabilities struct{}
// SamplingToolsCapabilities indicates the client supports tool use in sampling.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingToolsCapabilities struct{}
// ToolChoice controls how the model uses tools during sampling.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type ToolChoice struct {
// Mode controls tool invocation behavior:
// - "auto": Model decides whether to use tools (default)
@ -1721,6 +1831,11 @@ type URLElicitationCapabilities struct{}
//
// For assistant messages, Content may be text, image, audio, or tool_use.
// For user messages, Content may be text, image, audio, or tool_result.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SamplingMessage struct {
Content Content `json:"content"`
Role Role `json:"role"`
@ -1746,6 +1861,12 @@ func (m *SamplingMessage) UnmarshalJSON(data []byte) error {
return nil
}
// SetLoggingLevelParams holds parameters for a logging/setLevel request.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type SetLoggingLevelParams struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -2071,6 +2192,11 @@ type Implementation struct {
type CompletionCapabilities struct{}
// LoggingCapabilities describes the server's support for sending log messages to the client.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
type LoggingCapabilities struct{}
// PromptCapabilities describes the server's support for prompts.
@ -2114,6 +2240,11 @@ type ServerCapabilities struct {
// suggestions.
Completions *CompletionCapabilities `json:"completions,omitempty"`
// Logging is present if the server supports log messages.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
Logging *LoggingCapabilities `json:"logging,omitempty"`
// Prompts is present if the server supports prompts.
Prompts *PromptCapabilities `json:"prompts,omitempty"`
@ -2196,6 +2327,11 @@ const (
// MetaKeyClientCapabilities carries the client's [ClientCapabilities].
MetaKeyClientCapabilities = "io.modelcontextprotocol/clientCapabilities"
// MetaKeyLogLevel identifies the desired log level for the request.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
MetaKeyLogLevel = "io.modelcontextprotocol/logLevel"
// MetaKeySubscriptionID identifies the subscriptions/listen request that an
// out-of-band notification belongs to.

2
mcp/sampling_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 sampling APIs.
package mcp
// TODO: move other sampling-related tests to this file.

49
mcp/server.go
View file

@ -73,6 +73,12 @@ type ServerOptions struct {
// If zero, defaults to [DefaultPageSize].
PageSize int
// If non-nil, called when "notifications/roots/list_changed" is received.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation
// window (at least twelve months). Migrate to passing paths via tool
// parameters, resource URIs, or configuration. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
RootsListChangedHandler func(context.Context, *RootsListChangedRequest)
// If non-nil, called when "notifications/progress" is received.
ProgressNotificationHandler func(context.Context, *ProgressNotificationServerRequest)
@ -1474,6 +1480,12 @@ func (ss *ServerSession) Ping(ctx context.Context, params *PingParams) error {
}
// ListRoots lists the client roots.
//
// Deprecated: the roots feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to passing paths via tool parameters,
// resource URIs, or configuration. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (ss *ServerSession) ListRoots(ctx context.Context, params *ListRootsParams) (*ListRootsResult, error) {
if err := ss.checkInitialized(methodListRoots); err != nil {
return nil, err
@ -1486,6 +1498,12 @@ func (ss *ServerSession) ListRoots(ctx context.Context, params *ListRootsParams)
// If the client returns multiple content blocks (e.g. parallel tool calls),
// CreateMessage returns an error. Use [ServerSession.CreateMessageWithTools]
// for tool-enabled sampling.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to calling LLM provider APIs directly
// from your server. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (ss *ServerSession) CreateMessage(ctx context.Context, params *CreateMessageParams) (*CreateMessageResult, error) {
if err := ss.checkInitialized(methodCreateMessage); err != nil {
return nil, err
@ -1523,6 +1541,12 @@ func (ss *ServerSession) CreateMessage(ctx context.Context, params *CreateMessag
// returning a [CreateMessageWithToolsResult] that supports array content
// (for parallel tool calls). Use this instead of [ServerSession.CreateMessage]
// when the request includes tools.
//
// Deprecated: the sampling feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). Migrate to calling LLM provider APIs directly
// from your server. See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (ss *ServerSession) CreateMessageWithTools(ctx context.Context, params *CreateMessageWithToolsParams) (*CreateMessageWithToolsResult, error) {
if err := ss.checkInitialized(methodCreateMessage); err != nil {
return nil, err
@ -1609,28 +1633,21 @@ func (ss *ServerSession) Elicit(ctx context.Context, params *ElicitParams) (*Eli
return res, nil
}
// logLevelContextKey carries the per-request log level from
// [ServerSession.handle] to [ServerSession.Log] for new-protocol
// (>= 2026-07-28) requests. The level is scoped to a single in-flight request
// — including handler goroutines that call [ServerSession.Log] concurrently —
// rather than to the session, which avoids races between concurrent requests
// and aligns with SEP-2575's per-request opt-in model. The value type is
// [LoggingLevel]; an empty string means the request opted out of log messages.
type logLevelContextKey struct{}
// Log sends a log message to the client.
//
// For new-protocol (>= 2026-07-28) requests, the level is taken from the
// originating request's `_meta` field (SEP-2575); an absent or empty value
// suppresses the message per spec. For old-protocol requests, the level is
// taken from the session state set via `logging/setLevel`.
//
// Deprecated: the logging feature is deprecated as of protocol version
// 2026-07-28 (SEP-2577). It remains functional during the deprecation window
// (at least twelve months). See
// https://modelcontextprotocol.io/seps/2577-deprecate-roots-sampling-and-logging.
func (ss *ServerSession) Log(ctx context.Context, params *LoggingMessageParams) error {
logLevel, ok := ctx.Value(logLevelContextKey{}).(LoggingLevel)
if !ok {
ss.mu.Lock()
logLevel = ss.state.LogLevel
ss.mu.Unlock()
}
ss.mu.Lock()
logLevel := ss.state.LogLevel
ss.mu.Unlock()
if logLevel == "" {
// The spec is unclear, but seems to imply that no log messages are sent until the client
// sets the level.
@ -1806,7 +1823,7 @@ func (ss *ServerSession) handle(ctx context.Context, req *jsonrpc.Request) (any,
ctx = context.WithValue(ctx, idContextKey{}, req.ID)
// For new-protocol requests, propagate the per-request log level.
if validatedMeta.usesNewProtocol {
ctx = context.WithValue(ctx, logLevelContextKey{}, validatedMeta.logLevel)
ss.setLevel(ctx, &SetLoggingLevelParams{Level: validatedMeta.logLevel})
}
return handleReceive(ctx, ss, req)
}

2
mcp/server_example_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 examples exercise deprecated SEP-2577 logging APIs for demonstration.
package mcp_test
import (

2
mcp/streamable_test.go
View file

@ -2,6 +2,8 @@
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
//lint:file-ignore SA1019 tests exercise deprecated SEP-2577 APIs (roots, sampling, logging).
package mcp
import (