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Roslyn Workbench MCP

Roslyn Workbench MCP

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Workspace Open

workspace-open

Loads a solution or project for inspection and staged mutation, evaluating MSBuild logic so source documents become queryable and code actions can run.

Instructions

Loads an additional workspace for inspection and, when enabled by Host policy, staged mutation. Open only a fully trusted workspace: loading evaluates MSBuild project logic, evaluated source inputs including external linked or package-provided documents become queryable, and later diagnostic or Code Action operations can load and execute project analysers with the Host's permissions. Documents outside workspaceRoot remain read-only. If instance status reports that the workspace is or may be in use elsewhere, use it only for necessary queries, expect results to become stale, and coordinate mutation ownership before starting a transaction.

Input Schema

NameRequiredDescriptionDefault
pathYesThe absolute solution or project path to load.
aliasNoThe optional caller-friendly alias for the workspace.
workspaceRootNoThe optional absolute repository or workspace root used for coordination and transaction boundaries.
msBuildPropertiesNoThe optional allowlisted MSBuild global properties used to evaluate this workspace.

Output Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.0.4
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
+  "$defs": {
+    "warningInfo": {
+      "properties": {
+        "code": {
+          "description": "The stable machine-readable warning code.",
+          "type": "string"
+        },
+        "message": {
+          "description": "The human-readable warning message.",
+          "type": "string"
+        }
+      },
+      "required": [
+        "code",
+        "message"
+      ],
+      "type": "object"
+    }
+  },
+  "oneOf": [
+    {
+      "properties": {
+        "data": {
+          "description": "Tool-specific result payload.",
+          "properties": {
+            "documentCount": {
+              "description": "The loaded document count.",
+              "type": "integer"
+            },
+            "loadDiagnostics": {
+              "description": "Workspace load and advisory status diagnostics.",
+              "items": {
+                "properties": {
+                  "id": {
+                    "description": "The diagnostic identifier.",
+                    "type": "string"
+                  },
+                  "location": {
+                    "description": "The optional source location of the diagnostic.",
+                    "properties": {
+                      "column": {
+                        "description": "The one-based column number.",
+                        "type": "integer"
+                      },
+                      "document": {
+                        "description": "The resolved document.",
+                        "properties": {
+                          "documentId": {
+                            "description": "The document identifier.",
+                            "type": "string"
+                          },
+                          "path": {
+                            "description": "The normalized document path.",
+                            "type": "string"
+                          },
+                          "projectId": {
+                            "description": "The owning project identifier.",
+                            "type": "string"
+                          }
+                        },
+                        "required": [
+                          "documentId",
+                          "path",
+                          "projectId"
+                        ],
+                        "type": [
+                          "object",
+                          "null"
+                        ]
+                      },
+                      "line": {
+                        "description": "The one-based line number.",
+                        "type": "integer"
+                      },
+                      "selector": {
+                        "description": "The canonical selector that can resolve this source location again.",
+                        "properties": {
+                          "span": {
+                            "properties": {
+                              "document": {
+                                "description": "Provide exactly one of path or documentId.",
+                                "properties": {
+                                  "documentId": {
+                                    "description": "Workspace-local document ID.",
+                                    "type": [
+                                      "string",
+                                      "null"
+                                    ]
+                                  },
+                                  "path": {
+                                    "description": "Workspace-relative path.",
+                                    "type": [
+                                      "string",
+                                      "null"
+                                    ]
+                                  },
+                                  "project": {
+                                    "description": "Disambiguates documents with matching paths or IDs.",
+                                    "properties": {
+                                      "name": {
+                                        "type": [
+                                          "string",
+                                          "null"
+                                        ]
+                                      },
+                                      "path": {
+                                        "description": "Workspace-relative path.",
+                                        "type": [
+                                          "string",
+                                          "null"
+                                        ]
+                                      },
+                                      "projectId": {
+                                        "type": [
+                                          "string",
+                                          "null"
+                                        ]
+                                      },
+                                      "targetFramework": {
+                                        "type": [
+                                          "string",
+                                          "null"
+                                        ]
+                                      }
+                                    },
+                                    "type": [
+                                      "object",
+                                      "null"
+                                    ]
+                                  }
+                                },
+                                "type": "object"
+                              },
+                              "range": {
+                                "description": "Zero-based UTF-16 range.",
+                                "properties": {
+                                  "length": {
+                                    "description": "UTF-16 code-unit length.",
+                                    "maximum": 2147483647,
+                                    "minimum": 0,
+                                    "type": "integer"
+                                  },
+                                  "start": {
+                                    "description": "Zero-based UTF-16 offset.",
+                                    "maximum": 2147483647,
+                                    "minimum": 0,
+                                    "type": "integer"
+                                  }
+                                },
+                                "type": "object"
+                              }
+                            },
+                            "required": [
+                              "document",
+                              "range"
+                            ],
+                            "type": "object"
+                          }
+                        },
+                        "required": [
+                          "span"
+                        ],
+                        "type": [
+                          "object",
+                          "null"
+                        ]
+                      },
+                      "snapshot": {
+                        "description": "The exact immutable workspace snapshot associated with this location.",
+                        "properties": {
+                          "snapshotId": {
+                            "format": "uuid",
+                            "type": "string"
+                          },
+                          "transactionRevision": {
+                            "type": [
+                              "integer",
+                              "null"
+                            ]
+                          },
+                          "workspaceEpoch": {
+                            "type": "integer"
+                          },
+                          "workspaceId": {
+                            "format": "uuid",
+                            "type": "string"
+                          }
+                        },
+                        "required": [
+                          "workspaceId",
+                          "workspaceEpoch",
+                          "snapshotId",
+                          "transactionRevision"
+                        ],
+                        "type": "object"
+                      },
+                      "span": {
+                        "description": "The resolved text span.",
+                        "properties": {
+                          "length": {
+                            "description": "UTF-16 code-unit length.",
+                            "maximum": 2147483647,
+                            "minimum": 0,
+                            "type": "integer"
+                          },
+                          "start": {
+                            "description": "Zero-based UTF-16 offset.",
+                            "maximum": 2147483647,
+                            "minimum": 0,
+                            "type": "integer"
+                          }
+                        },
+                        "type": [
+                          "object",
+                          "null"
+                        ]
+                      }
+                    },
+                    "required": [
+                      "snapshot"
+                    ],
+                    "type": [
+                      "object",
+                      "null"
+                    ]
+                  },
+                  "message": {
+                    "description": "The diagnostic message.",
+                    "type": "string"
+                  },
+                  "severity": {
+                    "description": "The diagnostic severity.",
+                    "enum": [
+                      "Hidden",
+                      "Info",
+                      "Warning",
+                      "Error"
+                    ],
+                    "type": "string"
+                  }
+                },
+                "required": [
+                  "id",
+                  "message"
+                ],
+                "type": "object"
+              },
+              "type": "array"
+            },
+            "projectCount": {
+              "description": "The loaded project count.",
+              "type": "integer"
+            },
+            "workspace": {
+              "description": "The loaded workspace identity.",
+              "properties": {
+                "alias": {
+                  "description": "The optional caller-friendly alias.",
+                  "type": [
+                    "string",
+                    "null"
+                  ]
+                },
+                "loadedPath": {
+                  "description": "The absolute path of the loaded workspace.",
+                  "type": "string"
+                },
+                "workspaceEpoch": {
+                  "description": "The workspace epoch for the loaded baseline.",
+                  "type": "integer"
+                },
+                "workspaceId": {
+                  "description": "The stable server-generated workspace identifier.",
+                  "format": "uuid",
+                  "type": "string"
+                },
+                "workspaceRoot": {
+                  "description": "The absolute repository or workspace root used for coordination and transaction boundaries.",
+                  "type": "string"
+                }
+              },
+              "required": [
+                "loadedPath",
+                "workspaceRoot"
+              ],
+              "type": [
+                "object",
+                "null"
+              ]
+            }
+          },
+          "type": [
+            "object",
+            "null"
+          ]
+        },
+        "ok": {
+          "const": true,
+          "description": "Whether the tool invocation succeeded."
+        },
+        "snapshot": {
+          "description": "Exact immutable workspace snapshot associated with the result, when available.",
+          "properties": {
+            "snapshotId": {
+              "format": "uuid",
+              "type": "string"
+            },
+            "transactionRevision": {
+              "type": [
+                "integer",
+                "null"
+              ]
+            },
+            "workspaceEpoch": {
+              "type": "integer"
+            },
+            "workspaceId": {
+              "format": "uuid",
+              "type": "string"
+            }
+          },
+          "required": [
+            "workspaceId",
+            "workspaceEpoch",
+            "snapshotId",
+            "transactionRevision"
+          ],
+          "type": "object"
+        },
+        "warnings": {
+          "description": "Non-fatal warnings the agent should consider.",
+          "items": {
+            "$ref": "#/$defs/warningInfo"
+          },
+          "type": "array"
+        }
+      },
+      "required": [
+        "ok",
+        "data"
+      ],
+      "type": "object"
+    },
+    {
+      "properties": {
+        "continuation": {
+          "description": "Action the agent should take before retrying or continuing.",
+          "oneOf": [
+            {
+              "additionalProperties": false,
+              "properties": {
+                "instruction": {
+                  "description": "Agent-facing instruction explaining how to continue.",
+                  "minLength": 1,
+                  "type": "string"
+                },
+                "kind": {
+                  "const": "CallTool",
+                  "description": "Action required before the original request can continue."
+                },
+                "tool": {
+                  "description": "Tool to call before continuing the original request.",
+                  "minLength": 1,
+                  "type": "string"
+                }
+              },
+              "required": [
+                "kind",
+                "tool",
+                "instruction"
+              ],
+              "type": "object"
+            },
+            {
+              "additionalProperties": false,
+              "properties": {
+                "instruction": {
+                  "description": "Agent-facing instruction explaining how to continue.",
+                  "minLength": 1,
+                  "type": "string"
+                },
+                "kind": {
+                  "const": "ChooseTool",
+                  "description": "Action required before the original request can continue."
+                },
+                "tools": {
+                  "description": "Allowed tool choices from which the agent must select one.",
+                  "items": {
+                    "description": "Name of a tool the agent may choose.",
+                    "minLength": 1,
+                    "type": "string"
+                  },
+                  "minItems": 1,
+                  "type": "array",
+                  "uniqueItems": true
+                }
+              },
+              "required": [
+                "kind",
+                "tools",
+                "instruction"
+              ],
+              "type": "object"
+            },
+            {
+              "additionalProperties": false,
+              "properties": {
+                "instruction": {
+                  "description": "Agent-facing instruction explaining how to continue.",
+                  "minLength": 1,
+                  "type": "string"
+                },
+                "kind": {
+                  "const": "RetryRequest",
+                  "description": "Action required before the original request can continue."
+                }
+              },
+              "required": [
+                "kind",
+                "instruction"
+              ],
+              "type": "object"
+            },
+            {
+              "additionalProperties": false,
+              "properties": {
+                "instruction": {
+                  "description": "Agent-facing instruction explaining how to continue.",
+                  "minLength": 1,
+                  "type": "string"
+                },
+                "kind": {
+                  "const": "ReviseRequest",
+                  "description": "Action required before the original request can continue."
+                }
+              },
+              "required": [
+                "kind",
+                "instruction"
+              ],
+              "type": "object"
+            },
+            {
+              "additionalProperties": false,
+              "properties": {
+                "instruction": {
+                  "description": "Agent-facing instruction explaining how to continue.",
+                  "minLength": 1,
+                  "type": "string"
+                },
+                "kind": {
+                  "const": "ResolveExternally",
+                  "description": "Action required before the original request can continue."
+                }
+              },
+              "required": [
+                "kind",
+                "instruction"
+              ],
+              "type": "object"
+            }
+          ]
+        },
+        "diagnostics": {
+          "description": "Diagnostics that explain the failed invocation.",
+          "items": {
+            "properties": {
+              "id": {
+                "description": "The diagnostic identifier.",
+                "type": "string"
+              },
+              "location": {
+                "description": "The optional source location of the diagnostic.",
+                "properties": {
+                  "column": {
+                    "description": "The one-based column number.",
+                    "type": "integer"
+                  },
+                  "document": {
+                    "description": "The resolved document.",
+                    "properties": {
+                      "documentId": {
+                        "description": "The document identifier.",
+                        "type": "string"
+                      },
+                      "path": {
+                        "description": "The normalized document path.",
+                        "type": "string"
+                      },
+                      "projectId": {
+                        "description": "The owning project identifier.",
+                        "type": "string"
+                      }
+                    },
+                    "required": [
+                      "documentId",
+                      "path",
+                      "projectId"
+                    ],
+                    "type": [
+                      "object",
+                      "null"
+                    ]
+                  },
+                  "line": {
+                    "description": "The one-based line number.",
+                    "type": "integer"
+                  },
+                  "selector": {
+                    "description": "The canonical selector that can resolve this source location again.",
+                    "properties": {
+                      "span": {
+                        "properties": {
+                          "document": {
+                            "description": "Provide exactly one of path or documentId.",
+                            "properties": {
+                              "documentId": {
+                                "description": "Workspace-local document ID.",
+                                "type": [
+                                  "string",
+                                  "null"
+                                ]
+                              },
+                              "path": {
+                                "description": "Workspace-relative path.",
+                                "type": [
+                                  "string",
+                                  "null"
+                                ]
+                              },
+                              "project": {
+                                "description": "Disambiguates documents with matching paths or IDs.",
+                                "properties": {
+                                  "name": {
+                                    "type": [
+                                      "string",
+                                      "null"
+                                    ]
+                                  },
+                                  "path": {
+                                    "description": "Workspace-relative path.",
+                                    "type": [
+                                      "string",
+                                      "null"
+                                    ]
+                                  },
+                                  "projectId": {
+                                    "type": [
+                                      "string",
+                                      "null"
+                                    ]
+                                  },
+                                  "targetFramework": {
+                                    "type": [
+                                      "string",
+                                      "null"
+                                    ]
+                                  }
+                                },
+                                "type": [
+                                  "object",
+                                  "null"
+                                ]
+                              }
+                            },
+                            "type": "object"
+                          },
+                          "range": {
+                            "description": "Zero-based UTF-16 range.",
+                            "properties": {
+                              "length": {
+                                "description": "UTF-16 code-unit length.",
+                                "maximum": 2147483647,
+                                "minimum": 0,
+                                "type": "integer"
+                              },
+                              "start": {
+                                "description": "Zero-based UTF-16 offset.",
+                                "maximum": 2147483647,
+                                "minimum": 0,
+                                "type": "integer"
+                              }
+                            },
+                            "type": "object"
+                          }
+                        },
+                        "required": [
+                          "document",
+                          "range"
+                        ],
+                        "type": "object"
+                      }
+                    },
+                    "required": [
+                      "span"
+                    ],
+                    "type": [
+                      "object",
+                      "null"
+                    ]
+                  },
+                  "snapshot": {
+                    "description": "The exact immutable workspace snapshot associated with this location.",
+                    "properties": {
+                      "snapshotId": {
+                        "format": "uuid",
+                        "type": "string"
+                      },
+                      "transactionRevision": {
+                        "type": [
+                          "integer",
+                          "null"
+                        ]
+                      },
+                      "workspaceEpoch": {
+                        "type": "integer"
+                      },
+                      "workspaceId": {
+                        "format": "uuid",
+                        "type": "string"
+                      }
+                    },
+                    "required": [
+                      "workspaceId",
+                      "workspaceEpoch",
+                      "snapshotId",
+                      "transactionRevision"
+                    ],
+                    "type": "object"
+                  },
+                  "span": {
+                    "description": "The resolved text span.",
+                    "properties": {
+                      "length": {
+                        "description": "UTF-16 code-unit length.",
+                        "maximum": 2147483647,
+                        "minimum": 0,
+                        "type": "integer"
+                      },
+                      "start": {
+                        "description": "Zero-based UTF-16 offset.",
+                        "maximum": 2147483647,
+                        "minimum": 0,
+                        "type": "integer"
+                      }
+                    },
+                    "type": [
+                      "object",
+                      "null"
+                    ]
+                  }
+                },
+                "required": [
+                  "snapshot"
+                ],
+                "type": [
+                  "object",
+                  "null"
+                ]
+              },
+              "message": {
+                "description": "The diagnostic message.",
+                "type": "string"
+              },
+              "severity": {
+                "description": "The diagnostic severity.",
+                "enum": [
+                  "Hidden",
+                  "Info",
+                  "Warning",
+                  "Error"
+                ],
+                "type": "string"
+              }
+            },
+            "required": [
+              "id",
+              "message"
+            ],
+            "type": "object"
+          },
+          "type": "array"
+        },
+        "error": {
+          "description": "Structured error details when the invocation failed.",
+          "properties": {
+            "code": {
+              "description": "Stable machine-readable error code.",
+              "type": "string"
+            },
+            "correlationId": {
+              "description": "Correlation identifier for matching the failure to server-side diagnostics, when available.",
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "message": {
+              "description": "Human-readable explanation of the failure.",
+              "type": "string"
+            }
+          },
+          "required": [
+            "code",
+            "message"
+          ],
+          "type": "object"
+        },
+        "ok": {
+          "const": false,
+          "description": "Whether the tool invocation succeeded."
+        },
+        "warnings": {
+          "description": "Non-fatal warnings the agent should consider.",
+          "items": {
+            "$ref": "#/$defs/warningInfo"
+          },
+          "type": "array"
+        }
+      },
+      "required": [
+        "ok",
+        "error"
+      ],
+      "type": "object"
+    },
+    {
+      "properties": {
+        "diagnostics": {
+          "description": "Diagnostics that explain the failed invocation.",
+          "properties": {
+            "detailsAvailable": {
+              "const": true
+            },
+            "detailsTool": {
+              "const": "get-error-details"
+            }
+          },
+          "required": [
+            "detailsAvailable",
+            "detailsTool"
+          ],
+          "type": "object"
+        },
+        "error": {
+          "description": "Structured error details when the invocation failed.",
+          "properties": {
+            "code": {
+              "const": "UnhandledException"
+            },
+            "correlationId": {
+              "format": "uuid",
+              "type": "string"
+            },
+            "message": {
+              "const": "Tool execution failed."
+            }
+          },
+          "required": [
+            "code",
+            "message",
+            "correlationId"
+          ],
+          "type": "object"
+        },
+        "ok": {
+          "const": false,
+          "description": "Whether the tool invocation succeeded."
+        },
+        "reporting": {
+          "description": "Error-reporting workflow available for an unhandled failure.",
+          "properties": {
+            "canPrepare": {
+              "type": "boolean"
+            },
+            "prepareTool": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "state": {
+              "enum": [
+                "Available",
+                "AlwaysApproved",
+                "DisabledByConfiguration",
+                "ApprovalUnavailable"
+              ],
+              "type": "string"
+            }
+          },
+          "required": [
+            "state"
+          ],
+          "type": "object"
+        }
+      },
+      "required": [
+        "ok",
+        "error",
+        "diagnostics"
+      ],
+      "type": "object"
+    }
+  ],
+  "type": "object"
+}
  2. First observedv1.0.2

TDQS

A4.6/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Goes well beyond the annotations (readOnlyHint=false, destructiveHint=false, idempotentHint=false) by disclosing that loading evaluates MSBuild project logic, that external linked/package documents become queryable, that analysers can execute with Host permissions on later operations, and that documents outside workspaceRoot stay read-only. It also warns about staleness and mutation ownership when the workspace is shared — the exact risk context an agent needs before a non-idempotent load.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, front-loaded with the core action before the trust caveat and the concurrency caveat. The final sentence is dense but every clause carries risk information; a little tightening would still be possible without losing content.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present and 100% parameter coverage, the description only needs to cover trust, side effects and coordination — and it does exactly that, including analyser execution and staleness expectations. Nothing material to invoking this load safely is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds real meaning to workspaceRoot by tying it to read-only scope and transaction boundaries, and to the MSBuild properties by explaining they drive evaluation. It stops short of describing 'alias' or the artifact/configuration interplay, so it is an enhancement rather than full compensation.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Loads an additional workspace') plus the two modes it enables: inspection and, conditionally, staged mutation. This clearly separates it from siblings such as workspace-list, workspace-status, workspace-reload and workspace-close, which all operate on workspaces but with different intent.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit conditions: open only fully trusted workspaces, and if instance status reports the workspace is or may be in use elsewhere, restrict to necessary queries and coordinate mutation ownership. It does not point to workspace-list as the discovery path or state when to prefer workspace-reload versus a fresh open, but the when-to-use and when-to-be-cautious guidance is clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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