FlowiseAI/Flowise · error · Error

Received tool input did not match expected schema: ${JSON.st

Error message

Received tool input did not match expected schema: ${JSON.stringify(arg)}

What it means

Thrown inside the AgentAsTool StructuredTool._call when parseWithTypeConversion(this.schema, arg) rejects. The tool is a LangChain StructuredTool with a zod schema; arg is whatever the LLM emitted as the tool call input. The original parse error is swallowed and the raw arg is JSON-stringified so the caller can see what the model actually sent.

Source

Thrown at packages/components/nodes/tools/AgentAsTool/AgentAsTool.ts:284

        this.overrideConfig = overrideConfig
        this.returnDirect = returnDirect
    }

    async call(
        arg: z.infer<typeof this.schema>,
        configArg?: RunnableConfig | Callbacks,
        tags?: string[],
        flowConfig?: { sessionId?: string; chatId?: string; input?: string }
    ): Promise<string> {
        const config = parseCallbackConfigArg(configArg)
        if (config.runName === undefined) {
            config.runName = this.name
        }
        let parsed
        try {
            parsed = await parseWithTypeConversion(this.schema, arg)
        } catch (e) {
            throw new Error(`Received tool input did not match expected schema: ${JSON.stringify(arg)}`)
        }
        const callbackManager_ = await CallbackManager.configure(
            config.callbacks,
            this.callbacks,
            config.tags || tags,
            this.tags,
            config.metadata,
            this.metadata,
            { verbose: this.verbose }
        )
        const runManager = await callbackManager_?.handleToolStart(
            this.toJSON(),
            typeof parsed === 'string' ? parsed : JSON.stringify(parsed),
            undefined,
            undefined,
            undefined,
            undefined,
            config.runName

View on GitHub (pinned to abe4a8601a)

Solutions

1. Inspect the JSON-stringified arg in the error to see exactly what the model sent.
2. Tighten the tool's description and add a few-shot example so the model emits the expected shape.
3. Loosen the schema only where sensible (optional fields, defaults) so minor model deviations do not fail parsing.
4. Upgrade or switch to a model with stronger tool-calling support if errors are frequent.

Example fix

// before
try {
  parsed = await parseWithTypeConversion(this.schema, arg)
} catch (e) {
  throw new Error(`Received tool input did not match expected schema: ${JSON.stringify(arg)}`)
}
// after: keep the cause for debugging
try {
  parsed = await parseWithTypeConversion(this.schema, arg)
} catch (e) {
  const reason = e instanceof Error ? e.message : String(e)
  throw new Error(
    `Received tool input did not match expected schema: ${JSON.stringify(arg)} (reason: ${reason})`
  )
}

// Pre-validate the LLM payload shape before handing it to the tool
function preflightSchema(schema: z.ZodTypeAny, arg: unknown) {
  const r = schema.safeParse(arg)
  if (!r.success) throw new Error(`Preflight schema violation: ${r.error.message}`)
}

function looksLikeToolArg(v: unknown): v is Record<string, unknown> {
  return typeof v === 'object' && v !== null && !Array.isArray(v)
}

try {
  return await agentTool.invoke(arg)
} catch (e) {
  const msg = (e as Error).message
  if (msg.startsWith('Received tool input did not match')) {
    // feed the JSON-stringified arg back to the model with a corrective prompt
  } else throw e
}

When it happens

Trigger: The LLM emitted a JSON string instead of an object, omitted a required field, sent a wrong type (e.g. number where string expected), or produced malformed JSON that parseWithTypeConversion cannot coerce.

Common situations: Switching to a weaker model that does not reliably honor function-calling schemas; changing the tool's zod schema (e.g. adding a required field) without updating examples in the prompt; model timeouts that truncate the JSON payload.

Related errors

• Received tool input did not match expected schema: ${JSON.st
• Received tool input did not match expected schema
• Error parsing Zod Schema: ${exception}
• Received tool input did not match expected schema ${e}
• Unsupported type: ${typeInfo.base}

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/87bef2342177d9c6. Report an issue: GitHub.