grammar constrained sampling requires exactly one required s

Error message

grammar constrained sampling requires exactly one required string property

What it means

Error "grammar constrained sampling requires exactly one required string property" thrown in earendil-works/pi.

Source

Thrown at packages/ai/src/api/constrained-sampling.ts:195

		buffer.started = true;
	}
	delta += JSON.stringify(inputDelta).slice(1, -1);
	buffer.input = nextInput;

	if (close) {
		delta += '"}';
		buffer.closed = true;
	}
	return delta;
}

function inferGrammarInputProperty(tool: Tool): string {
	const schema = tool.parameters as JsonSchemaObject;
	if (schema.type !== "object") {
		throw new Error("grammar constrained sampling requires an object parameter schema");
	}
	if (!Array.isArray(schema.required) || schema.required.length !== 1 || typeof schema.required[0] !== "string") {
		throw new Error("grammar constrained sampling requires exactly one required string property");
	}

	const inputProperty = schema.required[0];
	if (!schema.properties?.[inputProperty]) {
		throw new Error(`grammar constrained sampling requires a properties entry for ${inputProperty}`);
	}
	if (schema.properties[inputProperty]?.type !== "string") {
		throw new Error(`grammar constrained sampling property ${inputProperty} must have type string`);
	}
	return inputProperty;
}

export function resolveJsonSchemaStrictSampling(tool: Tool, supportsStrictMode: boolean): boolean | undefined {
	const config = tool.constrainedSampling;
	if (!config || config.type !== "json_schema") return undefined;

	if (supportsStrictMode) {
		try {

View on GitHub (pinned to 4af9d21d3b)

Solutions

Declare exactly one required string property in the grammar tool schema.

When it happens

Trigger: Thrown at packages/ai/src/api/constrained-sampling.ts:195 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of earendil-works/pi@4af9d21d3b (2026-08-24). Data as JSON: /api/errors/6d999ebae31c5e80. Report an issue: GitHub.