Do I need API testing tools for a small internal service?

Not always.

For a small internal service, you may not need a dedicated API testing tool if:

• the service has only a few endpoints
• the API is stable and simple
• you can test it easily with unit/integration tests
• a browser, curl, or Postman-like manual checks are enough for occasional verification

You probably do want API testing tools if:

• you need repeatable regression tests
• multiple people depend on the service
• the service changes often
• you want to automate validation in CI/CD
• you need to test auth, error cases, or payload variations reliably

A practical rule:

• Very small/internal and low-risk: start with automated integration tests plus curl/Postman for manual checks
• Growing or business-critical: add an API testing tool/framework

Good lightweight options:

• curl / HTTPie for quick manual testing
• Postman / Insomnia for exploratory testing and sharing requests
• pytest + requests or similar for automated tests in code
• Newman if you want to run Postman collections in CI

If you want, I can suggest the simplest setup based on your stack and how many endpoints you have.