MCP Tools Reference: aiplatform.googleapis.com

Tool: corroborate_content

Evaluates the factuality of a piece of content (typically an LLM-generated response) against a set of facts from a RAG Engine Corpus, returning a per-claim citation score and supporting facts. Use this after a generation step when the user wants to verify groundedness, surface hallucinations, or attach citations to model output.

Differs from retrieve_contexts and augment_prompt: those happen before generation; corroborate_content happens after, on text the model already produced. Format: 'projects/{project_id}/locations/{region}'. CRITICAL: For {region}, use the region specified in the current context window. If no region is specified, prompt the user to provide one. Do not use 'global'.

Parameters * parent: The parent resource, of the form projects/{project}/locations/{location}. * content: The input content to corroborate, in Content form. Only text is supported. * facts: A list of facts to corroborate the content against. Typically obtained from a prior retrieve_contexts call. * parameters: Optional per-request parameter overrides. * parameters.citation_threshold: Only return claims whose citation score exceeds this threshold.

The following sample demonstrate how to use curl to invoke the corroborate_content MCP tool.

Curl Request 
                  
curl --location 'https://aiplatform.googleapis.com/mcp/generate' \
--header 'content-type: application/json' \
--header 'accept: application/json, text/event-stream' \
--data '{
  "method": "tools/call",
  "params": {
    "name": "corroborate_content",
    "arguments": {
      // provide these details according to the tool's MCP specification
    }
  },
  "jsonrpc": "2.0",
  "id": 1
}'

Input Schema

Request message for CorroborateContent.

CorroborateContentRequest

JSON representation 
{
  "parent": string,
  "facts": [
    {
      object (Fact)
    }
  ],
  "parameters": {
    object (Parameters)
  },

  // Union field _content can be only one of the following:
  "content": {
    object (Content)
  }
  // End of list of possible types for union field _content.
}
Fields
parent

string

Required. The resource name of the Location from which to corroborate text. The users must have permission to make a call in the project. Format: projects/{project}/locations/{location}.
facts[]

object (Fact)

Optional. Facts used to generate the text can also be used to corroborate the text.
parameters

object (Parameters)

Optional. Parameters that can be set to override default settings per request.

Union field _content.

_content can be only one of the following:
content

object (Content)

Optional. Input content to corroborate, only text format is supported for now.

Content

JSON representation 
{
  "role": string,
  "parts": [
    {
      object (Part)
    }
  ]
}
Fields
role

string

Optional. The producer of the content. Must be either 'user' or 'model'.

If not set, the service will default to 'user'.
parts[]

object (Part)

Required. A list of Part objects that make up a single message. Parts of a message can have different MIME types.

A Content message must have at least one Part.

Part

JSON representation 
{
  "thought": boolean,
  "thoughtSignature": string,
  "mediaResolution": {
    object (MediaResolution)
  },
  "audioTranscription": {
    object (AudioTranscription)
  },

  // Union field data can be only one of the following:
  "text": string,
  "inlineData": {
    object (Blob)
  },
  "fileData": {
    object (FileData)
  },
  "functionCall": {
    object (FunctionCall)
  },
  "functionResponse": {
    object (FunctionResponse)
  },
  "executableCode": {
    object (ExecutableCode)
  },
  "codeExecutionResult": {
    object (CodeExecutionResult)
  }
  // End of list of possible types for union field data.

  // Union field metadata can be only one of the following:
  "videoMetadata": {
    object (VideoMetadata)
  }
  // End of list of possible types for union field metadata.
}
Fields
thought

boolean

Optional. Indicates whether the part represents the model's thought process or reasoning.
thoughtSignature

string (bytes format)

Optional. An opaque signature for the thought so it can be reused in subsequent requests.

A base64-encoded string.
mediaResolution

object (MediaResolution)

per part media resolution. Media resolution for the input media.
audioTranscription

object (AudioTranscription)

Optional. Audio (input or output) transcription. This is only set when this Part contains audio data.

Union field data.

data can be only one of the following:
text

string

Optional. The text content of the part. When sent from the VSCode Gemini Code Assist extension, references to @mentioned items will be converted to markdown boldface text. For example @my-repo will be converted to and sent as **my-repo** by the IDE agent.
inlineData

object (Blob)

Optional. The inline data content of the part. This can be used to include images, audio, or video in a request.
fileData

object (FileData)

Optional. The URI-based data of the part. This can be used to include files from Google Cloud Storage.
functionCall

object (FunctionCall)

Optional. A predicted function call returned from the model. This contains the name of the function to call and the arguments to pass to the function.
functionResponse

object (FunctionResponse)

Optional. The result of a function call. This is used to provide the model with the result of a function call that it predicted.
executableCode

object (ExecutableCode)

Optional. Code generated by the model that is intended to be executed.
codeExecutionResult

object (CodeExecutionResult)

Optional. The result of executing the ExecutableCode.

Union field metadata.

metadata can be only one of the following:
videoMetadata

object (VideoMetadata)

Optional. Video metadata. The metadata should only be specified while the video data is presented in inline_data or file_data.

Blob

JSON representation 
{
  "mimeType": string,
  "data": string,
  "displayName": string
}
Fields
mimeType

string

Required. The IANA standard MIME type of the source data.
data

string (bytes format)

Required. The raw bytes of the data.

A base64-encoded string.
displayName

string

Optional. The display name of the blob. Used to provide a label or filename to distinguish blobs.

This field is only returned in PromptMessage for prompt management. It is used in the Gemini calls only when server-side tools (code_execution, google_search, and url_context) are enabled.

FileData

JSON representation 
{
  "mimeType": string,
  "fileUri": string,
  "displayName": string
}
Fields
mimeType

string

Required. The IANA standard MIME type of the source data.
fileUri

string

Required. The URI of the file in Google Cloud Storage.
displayName

string

Optional. The display name of the file. Used to provide a label or filename to distinguish files.

This field is only returned in PromptMessage for prompt management. It is used in the Gemini calls only when server side tools (code_execution, google_search, and url_context) are enabled.

FunctionCall

JSON representation 
{
  "id": string,
  "name": string,
  "args": {
    object
  },
  "partialArgs": [
    {
      object (PartialArg)
    }
  ],
  "willContinue": boolean
}
Fields
id

string

Optional. The unique id of the function call. If populated, the client to execute the function_call and return the response with the matching id.
name

string

Optional. The name of the function to call. Matches FunctionDeclaration.name.
args

object (Struct format)

Optional. The function parameters and values in JSON object format. See FunctionDeclaration.parameters for parameter details.
partialArgs[]

object (PartialArg)

Optional. The partial argument value of the function call. If provided, represents the arguments/fields that are streamed incrementally.
willContinue

boolean

Optional. Whether this is the last part of the FunctionCall. If true, another partial message for the current FunctionCall is expected to follow.

Struct

JSON representation 
{
  "fields": {
    string: value,
    ...
  }
}
Fields
fields

map (key: string, value: value (Value format))

Unordered map of dynamically typed values.

An object containing a list of "key": value pairs. Example: { "name": "wrench", "mass": "1.3kg", "count": "3" }.

FieldsEntry

JSON representation 
{
  "key": string,
  "value": value
}
Fields
key

string
value

value (Value format)

Value

JSON representation 
{

  // Union field kind can be only one of the following:
  "nullValue": null,
  "numberValue": number,
  "stringValue": string,
  "boolValue": boolean,
  "structValue": {
    object
  },
  "listValue": array
  // End of list of possible types for union field kind.
}
Fields
Union field kind. The kind of value. kind can be only one of the following:
nullValue

null

Represents a JSON null.
numberValue

number

Represents a JSON number. Must not be NaN, Infinity or -Infinity, since those are not supported in JSON. This also cannot represent large Int64 values, since JSON format generally does not support them in its number type.
stringValue

string

Represents a JSON string.
boolValue

boolean

Represents a JSON boolean (true or false literal in JSON).
structValue

object (Struct format)

Represents a JSON object.
listValue

array (ListValue format)

Represents a JSON array.

ListValue

JSON representation 
{
  "values": [
    value
  ]
}
Fields
values[]

value (Value format)

Repeated field of dynamically typed values.

PartialArg

JSON representation 
{
  "jsonPath": string,
  "willContinue": boolean,

  // Union field delta can be only one of the following:
  "nullValue": null,
  "numberValue": number,
  "stringValue": string,
  "boolValue": boolean
  // End of list of possible types for union field delta.
}
Fields
jsonPath

string

Required. A JSON Path (RFC 9535) to the argument being streamed. https://datatracker.ietf.org/doc/html/rfc9535. e.g. "$.foo.bar[0].data".
willContinue

boolean

Optional. Whether this is not the last part of the same json_path. If true, another PartialArg message for the current json_path is expected to follow.
Union field delta. The delta of field value being streamed. delta can be only one of the following:
nullValue

null

Optional. Represents a null value.
numberValue

number

Optional. Represents a double value.
stringValue

string

Optional. Represents a string value.
boolValue

boolean

Optional. Represents a boolean value.

FunctionResponse

JSON representation 
{
  "id": string,
  "name": string,
  "response": {
    object
  },
  "parts": [
    {
      object (FunctionResponsePart)
    }
  ]
}
Fields
id

string

Optional. The id of the function call this response is for. Populated by the client to match the corresponding function call id.
name

string

Required. The name of the function to call. Matches FunctionDeclaration.name and FunctionCall.name.
response

object (Struct format)

Required. The function response in JSON object format. Use "output" key to specify function output and "error" key to specify error details (if any). If "output" and "error" keys are not specified, then whole "response" is treated as function output.
parts[]

object (FunctionResponsePart)

Optional. Ordered Parts that constitute a function response. Parts may have different IANA MIME types.

FunctionResponsePart

JSON representation 
{

  // Union field data can be only one of the following:
  "inlineData": {
    object (FunctionResponseBlob)
  },
  "fileData": {
    object (FunctionResponseFileData)
  }
  // End of list of possible types for union field data.
}
Fields
Union field data. The data of the function response part. data can be only one of the following:
inlineData

object (FunctionResponseBlob)

Inline media bytes.
fileData

object (FunctionResponseFileData)

URI based data.

FunctionResponseBlob

JSON representation 
{
  "mimeType": string,
  "data": string,
  "displayName": string
}
Fields
mimeType

string

Required. The IANA standard MIME type of the source data.
data

string (bytes format)

Required. Raw bytes.

A base64-encoded string.
displayName

string

Optional. Display name of the blob.

Used to provide a label or filename to distinguish blobs.

This field is only returned in PromptMessage for prompt management. It is currently used in the Gemini GenerateContent calls only when server side tools (code_execution, google_search, and url_context) are enabled.

FunctionResponseFileData

JSON representation 
{
  "mimeType": string,
  "fileUri": string,
  "displayName": string
}
Fields
mimeType

string

Required. The IANA standard MIME type of the source data.
fileUri

string

Required. URI.
displayName

string

Optional. Display name of the file data.

Used to provide a label or filename to distinguish file datas.

This field is only returned in PromptMessage for prompt management. It is currently used in the Gemini GenerateContent calls only when server side tools (code_execution, google_search, and url_context) are enabled.

ExecutableCode

JSON representation 
{
  "language": enum (Language),
  "code": string,

  // Union field _id can be only one of the following:
  "id": string
  // End of list of possible types for union field _id.
}
Fields
language

enum (Language)

Required. Programming language of the code.
code

string

Required. The code to be executed.

Union field _id.

_id can be only one of the following:
id

string

Optional. Unique identifier of the ExecutableCode part. The server returns the CodeExecutionResult with the matching id.

CodeExecutionResult

JSON representation 
{
  "outcome": enum (Outcome),
  "output": string,

  // Union field _id can be only one of the following:
  "id": string
  // End of list of possible types for union field _id.
}
Fields
outcome

enum (Outcome)

Required. Outcome of the code execution.
output

string

Optional. Contains stdout when code execution is successful, stderr or other description otherwise.

Union field _id.

_id can be only one of the following:
id

string

Optional. The identifier of the ExecutableCode part this result is for. Only populated if the corresponding ExecutableCode has an id.

VideoMetadata

JSON representation 
{
  "startOffset": string,
  "endOffset": string,
  "fps": number
}
Fields
startOffset

string (Duration format)

Optional. The start offset of the video.

A duration in seconds with up to nine fractional digits, ending with 's'. Example: "3.5s".
endOffset

string (Duration format)

Optional. The end offset of the video.

A duration in seconds with up to nine fractional digits, ending with 's'. Example: "3.5s".
fps

number

Optional. The frame rate of the video sent to the model. If not specified, the default value is 1.0. The valid range is (0.0, 24.0].

Duration

JSON representation 
{
  "seconds": string,
  "nanos": integer
}
Fields
seconds

string (int64 format)

Signed seconds of the span of time. Must be from -315,576,000,000 to +315,576,000,000 inclusive. Note: these bounds are computed from: 60 sec/min * 60 min/hr * 24 hr/day * 365.25 days/year * 10000 years
nanos

integer

Signed fractions of a second at nanosecond resolution of the span of time. Durations less than one second are represented with a 0 seconds field and a positive or negative nanos field. For durations of one second or more, a non-zero value for the nanos field must be of the same sign as the seconds field. Must be from -999,999,999 to +999,999,999 inclusive.

MediaResolution

JSON representation 
{

  // Union field value can be only one of the following:
  "level": enum (Level)
  // End of list of possible types for union field value.
}
Fields

Union field value.

value can be only one of the following:
level

enum (Level)

The tokenization quality used for given media.

AudioTranscription

JSON representation 
{
  "text": string,
  "speakerLabel": string,
  "words": [
    {
      object (WordInfo)
    }
  ]
}
Fields
text

string

Required. The transcription text of this audio segment.
speakerLabel

string

Optional. A label identifying the speaker of this audio segment (e.g. "spk_1", "spk_2"). Present when diarization is set.
words[]

object (WordInfo)

Optional. Detailed word-level transcriptions and timing details. Present when word_timestamp is set.

WordInfo

JSON representation 
{
  "word": string,
  "startOffset": string,
  "endOffset": string
}
Fields
word

string

Required. Transcript of the word.
startOffset

string (Duration format)

Optional. Start offset in time of the word relative to the start of the audio.

A duration in seconds with up to nine fractional digits, ending with 's'. Example: "3.5s".
endOffset

string (Duration format)

Optional. End offset in time of the word relative to the start of the audio.

A duration in seconds with up to nine fractional digits, ending with 's'. Example: "3.5s".

Fact

JSON representation 
{

  // Union field _query can be only one of the following:
  "query": string
  // End of list of possible types for union field _query.

  // Union field _title can be only one of the following:
  "title": string
  // End of list of possible types for union field _title.

  // Union field _uri can be only one of the following:
  "uri": string
  // End of list of possible types for union field _uri.

  // Union field _summary can be only one of the following:
  "summary": string
  // End of list of possible types for union field _summary.

  // Union field _vector_distance can be only one of the following:
  "vectorDistance": number
  // End of list of possible types for union field _vector_distance.

  // Union field _score can be only one of the following:
  "score": number
  // End of list of possible types for union field _score.

  // Union field _chunk can be only one of the following:
  "chunk": {
    object (RagChunk)
  }
  // End of list of possible types for union field _chunk.
}
Fields

Union field _query.

_query can be only one of the following:
query

string

Query that is used to retrieve this fact.

Union field _title.

_title can be only one of the following:
title

string

If present, it refers to the title of this fact.

Union field _uri.

_uri can be only one of the following:
uri

string

If present, this uri links to the source of the fact.

Union field _summary.

_summary can be only one of the following:
summary

string

If present, the summary/snippet of the fact.

Union field _vector_distance.

_vector_distance can be only one of the following:
vectorDistance
(deprecated)

number

If present, the distance between the query vector and this fact vector.

Union field _score.

_score can be only one of the following:
score

number

If present, according to the underlying Vector DB and the selected metric type, the score can be either the distance or the similarity between the query and the fact and its range depends on the metric type.

For example, if the metric type is COSINE_DISTANCE, it represents the distance between the query and the fact. The larger the distance, the less relevant the fact is to the query. The range is [0, 2], while 0 means the most relevant and 2 means the least relevant.

Union field _chunk.

_chunk can be only one of the following:
chunk

object (RagChunk)

If present, chunk properties.

RagChunk

JSON representation 
{
  "text": string,

  // Union field _page_span can be only one of the following:
  "pageSpan": {
    object (PageSpan)
  }
  // End of list of possible types for union field _page_span.
}
Fields
text

string

The content of the chunk.

Union field _page_span.

_page_span can be only one of the following:
pageSpan

object (PageSpan)

If populated, represents where the chunk starts and ends in the document.

PageSpan

JSON representation 
{
  "firstPage": integer,
  "lastPage": integer
}
Fields
firstPage

integer

Page where chunk starts in the document. Inclusive. 1-indexed.
lastPage

integer

Page where chunk ends in the document. Inclusive. 1-indexed.

Parameters

JSON representation 
{
  "citationThreshold": number
}
Fields
citationThreshold

number

Optional. Only return claims with citation score larger than the threshold.

NullValue

Represents a JSON null.

NullValue is a sentinel, using an enum with only one value to represent the null value for the Value type union.

A field of type NullValue with any value other than 0 is considered invalid. Most ProtoJSON serializers will emit a Value with a null_value set as a JSON null regardless of the integer value, and so will round trip to a 0 value.

Enums
NULL_VALUE Null value.

Language

Supported programming languages for the generated code.

Enums
LANGUAGE_UNSPECIFIED Unspecified language. This value should not be used.
PYTHON Python >= 3.10, with numpy and simpy available.

Outcome

Enumeration of possible outcomes of the code execution.

Enums
OUTCOME_UNSPECIFIED Unspecified status. This value should not be used.
OUTCOME_OK Code execution completed successfully. output contains the stdout, if any.
OUTCOME_FAILED Code execution failed. output contains the stderr and stdout, if any.
OUTCOME_DEADLINE_EXCEEDED Code execution ran for too long, and was cancelled. There may or may not be a partial output present.

Level

The media resolution level.

Enums
MEDIA_RESOLUTION_UNSPECIFIED Media resolution has not been set.
MEDIA_RESOLUTION_LOW Media resolution set to low.
MEDIA_RESOLUTION_MEDIUM Media resolution set to medium.
MEDIA_RESOLUTION_HIGH Media resolution set to high.
MEDIA_RESOLUTION_ULTRA_HIGH Media resolution set to ultra high. This is for image only.

Output Schema

Response message for CorroborateContent.

CorroborateContentResponse

JSON representation 
{
  "claims": [
    {
      object (Claim)
    }
  ],

  // Union field _corroboration_score can be only one of the following:
  "corroborationScore": number
  // End of list of possible types for union field _corroboration_score.
}
Fields
claims[]

object (Claim)

Claims that are extracted from the input content and facts that support the claims.

Union field _corroboration_score.

_corroboration_score can be only one of the following:
corroborationScore

number

Confidence score of corroborating content. Value is [0,1] with 1 is the most confidence.

Claim

JSON representation 
{
  "factIndexes": [
    integer
  ],

  // Union field _start_index can be only one of the following:
  "startIndex": integer
  // End of list of possible types for union field _start_index.

  // Union field _end_index can be only one of the following:
  "endIndex": integer
  // End of list of possible types for union field _end_index.

  // Union field _score can be only one of the following:
  "score": number
  // End of list of possible types for union field _score.
}
Fields
factIndexes[]

integer

Indexes of the facts supporting this claim.

Union field _start_index.

_start_index can be only one of the following:
startIndex

integer

Index in the input text where the claim starts (inclusive).

Union field _end_index.

_end_index can be only one of the following:
endIndex

integer

Index in the input text where the claim ends (exclusive).

Union field _score.

_score can be only one of the following:
score

number

Confidence score of this corroboration.

Tool Annotations

Destructive Hint: ❌ | Idempotent Hint: ✅ | Read Only Hint: ✅ | Open World Hint: ❌