Best Practices for Building Efficient and Scalable ServiceNow APIs

[sarah_bioni]

In ServiceNow development, building performant and maintainable APIs is critical for scalability, security, and integration. This article shares best practices for designing Scripted REST APIs and highlights when to leverage native Table APIs for optimal results.

✅ Prefer Native Table API Over Scripted REST

Whenever possible, use the Table API, which is available out-of-the-box and offers:

• Built-in security and performance optimizations
• Support for dot-walking, filtering, sorting, and pagination
• Reduced complexity and maintenance overhead

🛠️ Scripted REST API Optimization Tips

If you must use Scripted REST APIs, consider the following improvements:

1. Query Efficiency

• Avoid CONTAINS In large tables, it triggers full table scans.
  • Prefer STARTSWITH, =, or IN for indexed queries.
• Index fields used in queries to improve lookup speed.

2. GlideRecord Usage

• Use getValue() instead of getDisplayValue() unless a readable value is required.
• Avoid getElement() in loops—it’s heavier and impacts performance.
• Restrict the result size with gr.setLimit().

3. Parameter Validation

• Use gs.nil() to validate parameters robustly (handles null, undefined, empty).
• Validate input before using it in addQuery() to prevent injection risks.

4. Pagination

• Implement offset and limit parameters in API URLs.
• Avoid returning large datasets without pagination.

5. GlideAggregate for Metrics

• Use GlideAggregate for counts and sums instead of GlideRecord loops.

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🔐 Security and Maintainability

• Enable “Requires Authentication” on all endpoints.
• Configure ACLs to restrict access.

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🧩 Versioning and Endpoint Hygiene

• Always use versioned endpoints (e.g., /v1/, /v2/) for backward compatibility.

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🧪 Final Thoughts

Building APIs in ServiceNow is not just about exposing data—it’s about doing so securely, efficiently, and sustainably. By following these practices, developers can ensure their APIs are robust, scalable, and easy to maintain.

[rachidh74]

Great summary — these are exactly the fundamentals that keep ServiceNow APIs performant and maintainable over time.

One thing I often see in practice is that teams do many of these things at build time, but don’t always re-check them as APIs evolve, get reused, or integrated in new ways. Performance and security issues tend to creep in gradually.

That’s why I’ve found lightweight, read-only API testing helpful as a complement — not to replace best practices, but to periodically validate things like query patterns, auth settings, pagination, and overall exposure from the outside. It closes the loop between how an API was designed and how it actually behaves in production.

[James Fricker]

For REST table API GET calls, limit the columns to just those that you need. Some tables have over 100 columns and very often you only need less than 10% of those.

[Michal Fisera]

Hello,

I would like to challenge this best practice a little 🙂

In my opinion, whether the Table API or a Scripted REST API is the better choice largely depends on the use case, the environment, and the level of trust between the integrated systems.

From a maintainability perspective, the Table API is often the most efficient solution because it is available out of the box and requires minimal custom development. However, when looking at the topic from a security and governance perspective, the answer is not always that straightforward.

While access to the Table API can be controlled through roles and ACLs, this often requires additional configuration and ongoing maintenance to ensure that only the intended operations and data are exposed.

One of the biggest advantages of Scripted REST APIs is the ability to explicitly define and control the integration contract. You can expose only the fields and operations that are required, implement custom validation and business logic, and prevent consumers from accessing data or functionality beyond the intended scope.

From an audit and compliance perspective, Scripted REST APIs can also provide clearer evidence that the organization maintains full control over what is exposed externally and what actions can be performed.

For that reason, I would suggest that "prefer the Table API whenever possible" may be too broad of a recommendation. A more balanced approach could be:

Use the Table API when it naturally satisfies the integration requirements and security expectations. Use a Scripted REST API when stronger control over data exposure, validation, business logic, or the integration contract is required.

I'd be interested to hear how others balance maintainability versus security and governance concerns in their environments.