The Developer Agent — TDD Without Shortcuts
How Datarim's Developer agent implements features with test-driven discipline, follows the project's own patterns, and verifies its work before handing off.
The most common failure mode in AI-assisted coding is not wrong logic — it is correct logic that ignores the conventions the rest of the codebase already settled on. The Developer agent is built to avoid that: it reads the project's patterns before writing a single line, and it writes the tests before the code they will exercise.
This agent handles the implementation phase of a Datarim task. Its job is not to explore or review — it is to build: correctly, consistently, and in a way that a human engineer would recognize as their own codebase.
What it does
The Developer follows a test-driven cycle. A test is written first, it fails (red), then the implementation makes it pass (green), then a quick refactor cleans up what was just added. This rhythm catches contract violations early, when they are still cheap to fix.
Before writing anything, the agent reads the project's active context, its task definition, and the system patterns file that describes how the codebase is structured. Style drift — using a different naming convention, a different error-handling pattern, a different abstraction layer than the rest of the project — is treated as a defect, not a style preference.
For HTTP integrations, the agent applies specific defaults: circuit breakers exclude 4xx errors from their failure counts (except 408 and 429, which do signal downstream pressure), and recovery events are wired to the project's event hub rather than silently dropped.
One concrete example
A task adds a new endpoint that calls an external payment API. The Developer first writes a test asserting the endpoint returns the correct shape when the external call succeeds, and a second test asserting it returns a structured error when the call times out. Only then does the implementation go in. After the tests are green, a design-conformance check verifies that the circuit breaker's recovery event is actually wired — not just that the breaker class exists, but that the event fires and reaches the event hub.
Where it sits
The Developer runs at /dr-do, the implementation stage. It hands off to the QA layer — where the Tester agent runs the full test suite and the Reviewer validates against the Definition of Done. For simpler tasks the path goes straight to archive; for L3-L4 complexity it goes through the full QA and compliance cycle.
See the full agent roster on the Developer reference card, or read what Datarim is for the bigger picture.