Setting up MCP Problem Type Skeleton by guidorc · Pull Request #1569 · WebFuzzing/EvoMaster

guidorc · 2026-06-05T01:22:18Z

Summary

Introducing a minimal class and interface structure to support Model Context Protocol (MCP) servers as a new ProblemType. No functionality is implemented yet, all methods related to MCP servers will throw an exception.

The changes are conformant to the latest MCP protocol specification 2025-11-25, and targetting servers that use the streamableHTTP transport mechanism. At this point we'll only be considering the tools and resources capabilities of the MCP server under analysis.

Main Changes

EMConfig: adds MCP as an experimental ProblemType with a required bbTargetUrl validation guard
Main: minimal setup for MCP problem type (throws not yer supported error)
14 new classes/interfaces under core/.../problem/mcp/

Class hierarchy

McpClient (interface)
- HttpMcpClient — HTTP/JSON-RPC 2.0 transport (stubbed)
ApiWsSampler
- McpSampler — discovers capabilities, builds individuals (stubbed)
MainAction
- McpAction (abstract)
  - McpToolCallAction — calls a named tool with an ObjectGene payload
  - McpResourceReadAction — reads a resource/template by URI
Param
- McpInputParam — wraps the tool input ObjectGene
- McpUriParam — wraps the resource URI StringGene
ActionResult
- McpCallResult — carries the isError flag for one action execution
ApiWsIndividual
- McpIndividual — ordered sequence of McpActions; unit of search
FitnessFunction
- McpFitness (abstract)
  - McpBlackBoxFitness — blackbox coverage scoring (stubbed)

jgaleotti · 2026-06-05T20:47:16Z

+            children.map { it.copy() }.toMutableList() as MutableList<ActionComponent>,
+            mainSize = groupsView()!!.sizeOfGroup(GroupsOfChildren.MAIN),
+            sqlSize = groupsView()!!.sizeOfGroup(GroupsOfChildren.INITIALIZATION_SQL),
+            mongoSize = groupsView()!!.sizeOfGroup(GroupsOfChildren.INITIALIZATION_MONGO)


why not INITIALIZATION_DNS?

That would eventually be required for white-box testing when mocking the inner requests of a tool. But that is also the case for sqlSize and mongoSize, for now I believe we should remove those as well.

Copilot

Pull request overview

Introduces an initial Kotlin skeleton for supporting Model Context Protocol (MCP) servers as a new (experimental) EvoMaster ProblemType, adding placeholder client/action/individual/fitness/module types with stubbed behavior.

Changes:

Adds EMConfig.ProblemType.MCP (experimental) and enforces bbTargetUrl in black-box mode for MCP.
Adds minimal MCP domain model (actions, params, individuals, results) plus stubbed MCP client DTOs/client interface.
Adds a Guice module/sampler/fitness placeholders for a future MCP black-box workflow (currently stubbed/unsupported).

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
core/src/main/kotlin/org/evomaster/core/problem/mcp/service/McpSampler.kt	Adds MCP sampler skeleton (stubbed, initializes an HTTP MCP client).
core/src/main/kotlin/org/evomaster/core/problem/mcp/service/McpFitness.kt	Introduces MCP fitness base type for MCP individuals.
core/src/main/kotlin/org/evomaster/core/problem/mcp/service/McpBlackBoxModule.kt	Adds Guice bindings for MCP black-box components (sampler/fitness/etc).
core/src/main/kotlin/org/evomaster/core/problem/mcp/service/McpBlackBoxFitness.kt	Adds stubbed black-box fitness implementation for MCP.
core/src/main/kotlin/org/evomaster/core/problem/mcp/McpUriParam.kt	Adds Param wrapper for resource URI genes.
core/src/main/kotlin/org/evomaster/core/problem/mcp/McpToolCallAction.kt	Adds action representing an MCP tool call with object-gene payload.
core/src/main/kotlin/org/evomaster/core/problem/mcp/McpResourceReadAction.kt	Adds action representing an MCP resource read by URI.
core/src/main/kotlin/org/evomaster/core/problem/mcp/McpInputParam.kt	Adds Param wrapper for tool input genes.
core/src/main/kotlin/org/evomaster/core/problem/mcp/McpIndividual.kt	Adds MCP individual type (ordered sequence of MCP actions).
core/src/main/kotlin/org/evomaster/core/problem/mcp/McpCallResult.kt	Adds MCP action result type with `isError` flag.
core/src/main/kotlin/org/evomaster/core/problem/mcp/McpAction.kt	Adds base MCP action type extending `MainAction`.
core/src/main/kotlin/org/evomaster/core/problem/mcp/client/McpDTOs.kt	Adds minimal DTOs for MCP tools/resources/results.
core/src/main/kotlin/org/evomaster/core/problem/mcp/client/McpClient.kt	Adds MCP client interface (tools/resources + call/read).
core/src/main/kotlin/org/evomaster/core/problem/mcp/client/HttpMcpClient.kt	Adds stubbed HTTP MCP client implementation placeholder.
core/src/main/kotlin/org/evomaster/core/Main.kt	Adds `ProblemType.MCP` dispatch branch (currently throws unsupported).
core/src/main/kotlin/org/evomaster/core/EMConfig.kt	Adds MCP enum value and black-box `bbTargetUrl` validation.

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arcuri82

Hi @guidorc thx for your first PR!

arcuri82 · 2026-06-09T08:27:17Z

+
+    @PostConstruct
+    fun initialize() {
+        mcpClient = HttpMcpClient(config.bbTargetUrl)


use base, as bbTargetUrl is deprecated

arcuri82 · 2026-06-09T08:31:17Z

+    }
+
+    fun removeMcpActionAt(relativePosition: Int) {
+        killChildByIndex(relativePosition)


this might be wrong. might need to use removeMainActionGroupAt here

I believe you're right since we're using EnterpriseActionGroup

arcuri82 · 2026-06-09T08:33:28Z

+import org.evomaster.core.search.gene.string.StringGene
+
+class McpResourceReadAction(
+    val uri: StringGene,


what is the uri here? and does it need to be mutable in a gene?

Resources in MCP may be fixed or parametrized using URI templates, for example weather:///{city}/current where {city} is a variable. So we may want mutate the parameters. I'll research if stringGene is the appropiate type though.

arcuri82 · 2026-06-09T08:34:39Z

+import org.evomaster.core.search.gene.ObjectGene
+
+class McpToolCallAction(
+    val toolName: String,


recall that, once implementation is more stable, you will need to add JavaDcos for all those classes

arcuri82 · 2026-06-09T08:34:57Z

            if (problemType == ProblemType.GRAPHQL && bbTargetUrl.isBlank()) {
                throw ConfigProblemException("In black-box mode for GraphQL APIs, you must set the bbTargetUrl option")
            }
+            if (problemType == ProblemType.MCP && bbTargetUrl.isBlank()) {


Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

guido-rodriguez_sfemu and others added 2 commits June 4, 2026 21:59

Setting up MCP Problem Type Skeleton

ccd0ec7

Merge branch 'master' into feature/mcp-skeleton

a85ddc0

Pgarrett approved these changes Jun 5, 2026

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Pgarrett requested a review from jgaleotti June 5, 2026 13:00

jgaleotti requested changes Jun 5, 2026

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remove db related size from MCP individual

22d7dd7

jgaleotti approved these changes Jun 8, 2026

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jgaleotti requested review from arcuri82 and Copilot June 8, 2026 16:49

Copilot started reviewing on behalf of jgaleotti June 8, 2026 16:49 View session

Copilot AI reviewed Jun 8, 2026

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Comment thread core/src/main/kotlin/org/evomaster/core/Main.kt

Comment thread core/src/main/kotlin/org/evomaster/core/problem/mcp/McpResourceReadAction.kt

Comment thread core/src/main/kotlin/org/evomaster/core/problem/mcp/McpAction.kt

arcuri82 requested changes Jun 9, 2026

View reviewed changes

guidorc and others added 4 commits June 9, 2026 21:24

Fix for resource read action id

bc73377

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

feedback

d588c5d

Merge branch 'master' into feature/mcp-skeleton

f293d28

adjust resource read action parameters

ff5922c

guidorc requested a review from arcuri82 June 13, 2026 19:38

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Setting up MCP Problem Type Skeleton#1569

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guidorc commented Jun 5, 2026 •

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guidorc commented Jun 5, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

Main Changes

Class hierarchy

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guidorc commented Jun 5, 2026 •

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