Handlers and client/server methods take a single request argument
combining the session and params. This slightly simplifies the signature
for handlers, since there is no longer an often-ignored session
argument.
But more importantly, it opens the door to adding more information in
requests, such as auth info and HTTP request headers.
For #243.
As described in #272, there is really no reason for transports to be
closed structs with constructors, since their state must be established
by a call to Connect. Making them open structs simplifies their APIs,
and means that all transports can be extended in the future: we don't
have to create empty Options structs just for the purpose of future
compatibility.
For now, the related constructors and options structs are simply
deprecated (with go:fix directives where possible). A future CL will
remove them prior to the v1.0.0 release.
For #272
Support stateless streamable sessions by adding a GetSessionID function
to StreamableHTTPOptions. If GetSessionID returns "", the session is
stateless, and no validation is performed. This is implemented by
providing the session a trivial initialization state.
To implement this, some parts of #232 (distributed sessions) are copied
over, since they add an API for creating an already-initialized session.
In total, the following new API is added:
- StreamableHTTPOptions.GetSessionID
- ServerSessionOptions (a new parameter to Server.Connect)
- ServerSessionState
- ClientSessionOptions (a new parameter to Client.Connect, for symmetry)
For #10
Add a client example that lists all features on a stdio server. Since
this is our first client example, organize examples by client / server
-- otherwise it is too difficult to find client examples.
For #33
Add example of implementing mcp on [sequentialthinking
server](https://github.com/modelcontextprotocol/servers/tree/main/src/sequentialthinking),
from [Example Servers](https://modelcontextprotocol.io/examples).
The PR includes dynamic and reflective problem-solving through
structured thinking processes.
The server provides tools for:
- starting thinking sessions
- adding sequential thoughts with step tracking
- revising previous thoughts
- creating alternative reasoning branches
- reviewing complete processes.
Also, features include thread-safe session management, adaptive planning
that adjusts step counts dynamically.
Expose `jsonrpc2.MakeID`, `jsonrpc2.EncodeMessage` and
`jsonrpc2.DecodeMessage` functions to allow implementing custom
`mcp.Transport`.
Add an example that demonstrates a custom transport
implementation.
Fixes#110.
BREAKING CHANGE
Change the API for adding tools, prompts, resources and resource
templates to a server.
The ServerXXX types are gone along with the plural Add methods
(AddTools, AddPrompts etc.)
Instead there are single Add methods (AddTool, AddPrompt).
In addition, instead of NewServerTool, there is AddTool[In, Out].
Fixes#73.
This CL implements a completion handler for the server and a complete
method for the client.
Fixes: #12
<!-- Provide a brief summary of your changes -->
## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
This adds support for completion.
## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->
Added tests and an example.
## Breaking Changes
<!-- Will users need to update their code or configurations? -->
N/A
## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->
I added an example for how rate limiting should be implemented using
middleware.
Fixes#22
## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
Rate limiting can be enabled using middleware. This adds an example on
how to do that.
## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->
N/A
## Breaking Changes
<!-- Will users need to update their code or configurations? -->
No
## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update
## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->
After some experience with the flattened version of Content, we see that
it can easily lead to incorrect usage and is a harder API to read.
Therefore, this CL changes back to a design similar to what we had prior
to https://go.dev/cl/672415, though opting to promote content
unmarshalling to the protocol types that use it, which leads to an
overall simpler api.
* mcp: move to 2025-06-18 schema
Add types and fields for the latest MCP schema.
The main challenge here was dealing with the presence of _meta fields
on many types, like Tool, Prompt and Resource.
- Distinguish between the _meta field of a request's params, which
includes a progress token, from the _meta field on other types,
which is simply a map.
- Redefine GetMeta to return a pointer to the map. We wanted to avoid
that, but I don't see a clean way to do so. An alternative would be
to have GetMeta return a map, and SetMeta to set it.
- Provide GetProgressToken for requests only (not notifications or other
types).
- Still to do: deal with the meta and annotation fields of ContentBlock,
which are currently duplicated for Resource and ResourceContents.
* Meta and progress token redesign
In CL 682976, Alan Donovan correctly points out that the term in the MCP
spec is 'stdio', and therefore the correct capitalization is Stdio.
Change-Id: Ib5bbe04f1a61de886298b4d0adc13aefd6aadd9c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/683075
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Remove NewServerPrompt.
Schema inference is irrelevant for prompts.
All arguments are strings.
So using a struct is not as valuable as with tools.
The only advantage is catching misspellings at compile time.
It's not worth it.
Change-Id: I45aaa5d55c8940cc9e32dc277bd543f79d932519
Reviewed-on: https://go-review.googlesource.com/c/tools/+/682797
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
The hello example was using params.Name, which is the name of the
prompt. It should use args.Name.
Change-Id: I0e7e992bbe312fd5a6e56e9bc46a931f0eeb423c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/682416
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
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The NewTool and NewPrompt constructors were unidiomatic, because they
returned a ServerTool and ServerPrompt, respectively, rather than a Tool
and Prompt. Rename to be consistent with the constructed object name.
Change-Id: Ife3f16f783368401f792660c4272e1bb5ae61638
Reviewed-on: https://go-review.googlesource.com/c/tools/+/682375
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Reviewed-by: Jonathan Amsterdam <jba@google.com>
Add an (almost) complete implementation of the streamable HTTP
transport, including:
- A StreamableHTTPHandler for serving sessions.
- A StreamableHTTPServerTransport that supports session resumption.
- A minimal StreamableHTTPClientTransport.
Additionally, include the following minor changes:
- Refactor SSE event reading to use an iterator.
- Start to to aliases for JSON-RPC types (incomplete)
- Fix handling for null tool arguments (again)
Still to do:
- The streamable client does not support retry/resumption, or the
side-channel GET requests.
- Support configurable session and event retention (garbage collection).
- Expose the HTTP client used for HTTP requests (for auth).
Change-Id: Ieba216ef901169b4660d601386fa0c7c7bb4c4b2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/667515
Reviewed-by: Jonathan Amsterdam <jba@google.com>
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CallToolParams.Arguments is any.
Clients can send whatever they want.
Tool authors who create their own ToolHandler (bypassing NewTool)
will receive the arguments as a map[string]any which has been
validated against the input schema.
Tool authors who call NewTool can choose the type that the arguments
unmarshal into.
There is no double-unmarshaling and no downcasting.
There is no way for tool authors to avoid the unmarshal, and no way to
avoid the validation unless the omit an input schema, which is probably
bad for LLMs. If tool authors want this optimization, we can provide
it later.
Change-Id: Ieb201e56c7fb8a23bb1a93b27e946630ec9e79ad
Reviewed-on: https://go-review.googlesource.com/c/tools/+/679595
TryBot-Bypass: Jonathan Amsterdam <jba@google.com>
Auto-Submit: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Make Tool APIs future-proof by pushing generics into CallToolParams, and
using CallToolParams throughout. This has several advantages:
- We no longer need the awkward CallToolOptions type, which is almost
but not quite like CallToolParams.
- NewTool no longer needs to define its own handler type: it accepts a
ToolHandler[TArgs]. This also means its signature is future-proof.
Additionally, provide a `CallTool` helper (the analog of NewTool) to
serve as a more strongly typed variant of `ClientSession.CallTool`.
+ design, protocol generation
Change-Id: I80172a25bc50734dae84a541aa4776ed9161694e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/676495
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Auto-Submit: Robert Findley <rfindley@google.com>
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This uncovered a problem in how we represent resource results:
contents is a slice, not a single value.
I tried to use a file resource, but the server->client ListRoots
call didn't work because synthetic responses aren't supported.
Left a TODO.
I enhanced the hello example so I that could use the MCP Inspector to
work with resources.
The falseSchema change fixes a potential bug where schemas are
re-used, which is disallowed.
Change-Id: I1f0198043cb6221c2a03f4f83aa0bafbc71167f4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/677136
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
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Auto-Submit: Jonathan Amsterdam <jba@google.com>
Pass GetPromptParams as needed, in case that type ever gets additional
properties.
Change-Id: I83fa37bb2af5633a8c2bcdc47a85c3030dfe70fb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674895
Auto-Submit: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This change is necessary to support pagination which will be implemented
in subsequent CLs.
Change-Id: I8bc616a57463ea569dc7cadf1d4f06c69602ddd5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674135
Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Add a logical client session type back to the SDK, to bring it closer to
the design. Also, remove 'ConnectionOptions', which is better
implemented using middleware, and reimplement logging as a
LoggingTransport middleware, which is also added to the design.
Change-Id: I908b4f837d513ffc60ae5b6171a31519cffafebc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672795
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Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Bring the Server implementation up to date with the spec by renaming
ServerConnection to ServerSession. Also update variable names, which
were in various states of disarray from the multiple renamings of this
type.
Change-Id: I4aec883db6d0500fb91e6daa51b702614877cf8a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672655
Auto-Submit: Robert Findley <rfindley@google.com>
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Commit-Queue: Robert Findley <rfindley@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Use pointers for the protocol's struct types, to future-proof against
them getting large.
Change-Id: I55b204080a41c8140539697ba264e502e912e613
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672575
Reviewed-by: Robert Findley <rfindley@google.com>
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Now that the protocol package is merged into the mcp package, clean up
the higher level 'Content' union types, in favor of types constructors.
Change-Id: I37bedb0ff0a296eef799ba65c37ca7f94ee1dbbe
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672415
Reviewed-by: Jonathan Amsterdam <jba@google.com>
TryBot-Bypass: Jonathan Amsterdam <jba@google.com>
In accordance with the updated design, merge the protocol package into
the mcp package. To do so, rename protocol.Content to WireContent and
protocol.ResourceContents to WireResource.
Also, remove some stray logging in readResource.
Change-Id: I76f61ce8d67dd3ac520ef2e1959ade0a0785a480
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672375
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Reviewed-by: Jonathan Amsterdam <jba@google.com>
It's too confusing that you send server requests through the Client, and
send client requests through the ClientConnection. Rename
ClientConnection to ServerConnection, so that the types on the
server side of the control diagram start with 'Server'.
Change-Id: Idfd27af464a9296a2341cd23b2075cd9d0eb6b45
Reviewed-on: https://go-review.googlesource.com/c/tools/+/670538
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Auto-Submit: Robert Findley <rfindley@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
The generated protocol package is part of the SDK API, so it shouldn't
be internal.
Change-Id: I5306af48019b1599707b939b348eb6ae4f766ca9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/670356
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Reviewed-by: Jonathan Amsterdam <jba@google.com>
Add support for all content types, and formalize the conversion of
content to and from the wire format (as a discriminated union).
Change-Id: I93678ce98c02176a524d2c82425fb1267ad68bf0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/669135
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Add support for 'prompts/list' and 'prompts/get', and registering
prompts on the server using AddPrompts. Add a 'MakePrompt' helper to
construct prompts from a prompt handler using reflection.
Change-Id: I479cb9c9b99313cca99640c1f5ea1939363759e6
Reviewed-on: https://go-review.googlesource.com/c/tools/+/669015
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Reviewed-by: Jonathan Amsterdam <jba@google.com>
Implement variadic options for building tools and schemas, to allow
easier customization of tool input schemas.
Also, make fields required, unless they are marked as "omitempty".
Change-Id: I7a29258fae3ec5e7ea4906ed30ed6750979de962
Reviewed-on: https://go-review.googlesource.com/c/tools/+/668955
Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Based on my understanding, the getServer function is used to determine
which MCP server should be serving the session.
User might want to dynamically determine which MCP server to serve when
a new request comes in. In mcp/examples, two MCP servers are created
serving at the same port but under different URL "/greeter1",
"/greeter2". The MCP client will reach out to different URLs for
different MCP servers.
As a TODO, if the getServer() returns nil, the program will crash when
handing MCP request.
Change-Id: I4431266666e9ea28118e827a94eb1359b1fb3a81
Reviewed-on: https://go-review.googlesource.com/c/tools/+/668535
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Hongxiang Jiang <hxjiang@golang.org>
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Also validate that requests observe the lifecycle rules defined in the
spec.
Change-Id: I302282f81e053e76926e0bb295f7dbf8d526f02d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/667575
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Commit-Queue: Robert Findley <rfindley@google.com>
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Add support for SSE transport, as defined by version 2024-11-05 and
2025-03-26 of the MCP spec.
In order to achieve this, the jsonrpc2 stream must be abstracted so that
we can implement it across multiple HTTP requests. This required some
refactoring of the jsonrpc2_v2 package, so that we can avoid the
Dialer/Binder interfaces and construct the Connection directly from its
constituent primitives.
Change-Id: Id627b5b5a474d92f2c613cfad904d14611e7c768
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This CL contains an minimal prototype of an MCP SDK, using the
"new" jsonrpc2_v2 package (similar to x/exp/jsonrpc2).
Much is still yet to do, but this initial version addressed the
following aspects:
- Support for newline delimited JSONRPC2 framing, and message logging.
- A generated protocol package, containing type definitions to be used
in transport.
- A minimal jsonschema package to be used for both reading the MCP spec,
and for serving Tool input schemas.
- A transport abstraction, and two transport implementations: stdio, and
local (for testing).
- Client and Server types, to be configured with features and then
connected using their Connect methods, which return (respectively) a
ServerConnection and ClientConnection object.
- A minimal binding API for tools.
A catalog of things not yet done is in doc.go, but we should review this
CL eagerly, as it contains the fundamental building blocks of an
eventual SDK.
It is the intention that this package is more-or-less standalone, as it
may eventually be carved out into a separate repository. As such, its
only dependency within x/tools is jsonrpc2_v2, and the only change
required to that package is to expose a callback when the connection is
closed.
Change-Id: Ib66018961014f85a8884d56ab721d5642c98443c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/667036
Reviewed-by: Jonathan Amsterdam <jba@google.com>
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