Buy or Build: Third-party code evaluation

When tasked with implementing a new feature of any significant size, you are often faced with the decision of whether to use a library from a third party, or write your own solution. Here are a few factors that you should consider when making your choice.

The State of Development

  • How long has the library existed?
  • Is the library actively developed?
  • How often are new versions of the library released?
  • Has the library had a stable release?
  • Are breaking changes made to the library frequently?
  • Does the project follow semantic versioning?
  • Is there a published road map for future work with dates?
  • Are there pull requests that are frequently merged, or left unmerged?
  • Are there outstanding Github issues?

Library Dependencies

  • How many dependencies does the library have?
  • Are the dependencies up to date?
  • Are the required libraries of equal quality?


  • How well written is the library?
  • Does the library follow an established style guide?
  • Are code quality metrics available?
  • What is the level of test coverage?
  • Does the library have any known bugs?
  • Does the library follow industry standards?


  • Is the library based on a sound algorithmic approach?
  • What are the CPU, memory and network demands?
  • Is the approach novel, untested or well established?
  • Are there any potential security risks that could be introduced by the library?

Documentation / Ease of Use

  • Does the library have documentation, or will you be required to read the code to use it?
  • Are there learning resources such as books, training videos, or blog posts that can help you learn to use the library?
  • How long will it take you to learn the library's API?
  • Are there people on your team already familiar with the library?

Popularity / Community

  • What is the reputation of the authors for writing software?
  • How many contributors are there on the project?
  • What is the leadership model of the development team?
  • If the library is hosted on Github, how many stars and forks does it have?
  • Is the project company sponsored or are contributors paid to work on the library?
  • Is this library used in production by a companies?

Your Use Case

  • Does the library meet all the requirements?
  • Does the library provide more functionality than you will need?
  • Is the implementation efficient enough to handle your needs now, and into the future?
  • Can the library support extension in the future?
  • Are there switching costs that would prohibit moving to another library if needed?
  • Is there a license that enables reuse?
  • Does the library have licensing fees?

Adapted from a blog post of mine on the Square Root internal engineering blog