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Tool Validation

Tool validation checks that inputs are correct before executing the tool. Catching bad inputs early prevents wasted API calls, data corruption, and hard-to-debug errors.

8 min•By Priygop Team•Updated 2026

What to Validate

Required fields: check that all required parameters are present
Type checks: verify each parameter is the correct type (string, int, bool, list)
Range checks: numbers within valid ranges, strings within length limits
Format checks: email addresses, URLs, dates in expected format
Business rules: an end date must not be before a start date
Injection prevention: do not allow inputs that could run arbitrary code

Validation Example

# Tool with built-in input validation
from datetime import datetime

def search_orders(
    customer_email: str,
    start_date: str,
    end_date: str,
    status: str = "all"
) -> dict:
    """Search customer orders. Returns list of matching orders."""

    # Validate email
    if "@" not in customer_email or "." not in customer_email.split("@")[1]:
        return {"status": "error", "error": "Invalid email address format"}

    # Validate dates
    try:
        start = datetime.strptime(start_date, "%Y-%m-%d")
        end   = datetime.strptime(end_date,   "%Y-%m-%d")
    except ValueError:
        return {"status": "error", "error": "Dates must be in YYYY-MM-DD format"}

    if end < start:
        return {"status": "error", "error": "end_date must be after start_date"}

    # Validate status
    valid_statuses = {"all", "pending", "shipped", "delivered", "cancelled"}
    if status not in valid_statuses:
        return {"status": "error", "error": f"status must be one of: {valid_statuses}"}

    # All valid — proceed
    return {
        "status": "success",
        "customer": customer_email,
        "period": f"{start_date} to {end_date}",
        "filter": status,
        "records": []  # would come from DB in real implementation
    }

result = search_orders("user@example.com", "2024-01-01", "2024-12-31")
print(result["status"])

Key Takeaways

Tool validation checks that inputs are correct before executing the tool.
Required fields: check that all required parameters are present
Type checks: verify each parameter is the correct type (string, int, bool, list)
Range checks: numbers within valid ranges, strings within length limits

Topics in This Module

What to Validate

Required fields: check that all required parameters are present

Type checks: verify each parameter is the correct type (string, int, bool, list)

Range checks: numbers within valid ranges, strings within length limits

Format checks: email addresses, URLs, dates in expected format

Business rules: an end date must not be before a start date

Injection prevention: do not allow inputs that could run arbitrary code

Validation Example

# Tool with built-in input validation
from datetime import datetime

def search_orders(
    customer_email: str,
    start_date: str,
    end_date: str,
    status: str = "all"
) -> dict:
    """Search customer orders. Returns list of matching orders."""

    # Validate email
    if "@" not in customer_email or "." not in customer_email.split("@")[1]:
        return {"status": "error", "error": "Invalid email address format"}

    # Validate dates
    try:
        start = datetime.strptime(start_date, "%Y-%m-%d")
        end   = datetime.strptime(end_date,   "%Y-%m-%d")
    except ValueError:
        return {"status": "error", "error": "Dates must be in YYYY-MM-DD format"}

    if end < start:
        return {"status": "error", "error": "end_date must be after start_date"}

    # Validate status
    valid_statuses = {"all", "pending", "shipped", "delivered", "cancelled"}
    if status not in valid_statuses:
        return {"status": "error", "error": f"status must be one of: {valid_statuses}"}

    # All valid — proceed
    return {
        "status": "success",
        "customer": customer_email,
        "period": f"{start_date} to {end_date}",
        "filter": status,
        "records": []  # would come from DB in real implementation
    }

result = search_orders("user@example.com", "2024-01-01", "2024-12-31")
print(result["status"])

Topics in This Module