microsoft/vscode · error · Error

Invalid request: Tool call part must be followed by a User m

Error message

Invalid request: Tool call part must be followed by a User message with a LanguageModelToolResultPart with a matching callId.

What it means

Error "Invalid request: Tool call part must be followed by a User message with a LanguageModelToolResultPart with a matching callId." thrown in microsoft/vscode.

Source

Thrown at extensions/copilot/src/extension/conversation/vscode-node/languageModelAccess.ts:1023

	private validateRequest(_messages: Array<vscode.LanguageModelChatMessage | vscode.LanguageModelChatMessage2>): void {
		const lastMessage = _messages.at(-1);
		if (!lastMessage) {
			throw new Error('Invalid request: no messages.');
		}

		_messages.forEach((message, i) => {
			if (message.role === vscode.LanguageModelChatMessageRole.Assistant) {
				// Filter out DataPart since it does not share the same value type and does not have callId, function, etc.
				const filteredContent = message.content.filter(part => part instanceof vscode.LanguageModelDataPart);
				const toolCallIds = new Set(filteredContent
					.filter(part => part instanceof vscode.LanguageModelToolCallPart)
					.map(part => part.callId));
				let nextMessageIdx = i + 1;
				const errMsg = 'Invalid request: Tool call part must be followed by a User message with a LanguageModelToolResultPart with a matching callId.';
				while (toolCallIds.size > 0) {
					const nextMessage = _messages.at(nextMessageIdx++);
					if (!nextMessage || nextMessage.role !== vscode.LanguageModelChatMessageRole.User) {
						throw new Error(errMsg);
					}

					nextMessage.content.forEach(part => {
						if (!(part instanceof vscode.LanguageModelToolResultPart2 || part instanceof vscode.LanguageModelToolResultPart)) {
							throw new Error(errMsg);
						}

						toolCallIds.delete(part.callId);
					});
				}
			}
		});
	}
}


function or(...checks: ((value: unknown) => boolean)[]): (value: unknown) => boolean {
	return (value) => checks.some(check => check(value));

View on GitHub (pinned to a94b963a32)

When it happens

Trigger: Thrown at extensions/copilot/src/extension/conversation/vscode-node/languageModelAccess.ts:1023 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/vscode@a94b963a32 (2026-08-12). Data as JSON: /api/errors/9203dbae9607456c. Report an issue: GitHub.