# Developer API

- [Authentication](/developer-api/authentication.md): Learn how to authenticate to Simple OKR before you can use the APIs
- [Errors](/developer-api/errors.md): Error object structure and errors response codes
- [API Reference](/developer-api/api-reference.md)
- [Users](/developer-api/api-reference/users.md): User object holds information about a user of an organization.
- [Teams](/developer-api/api-reference/teams.md): Team objects are used to group users into teams.
- [Cycles](/developer-api/api-reference/cycles.md): Delivery cycles are used to organize objectives into time-bound groups. Delivery cycle is how we track performance and progress of your OKRs.
- [Objectives](/developer-api/api-reference/objectives.md): Objectives let you capture company, team or personal goals as part of the OKR process.
- [Key Results](/developer-api/api-reference/key-results.md): Key Results are quantitative metrics that let you track Objective's performance.