Source Driven Development

Overview

Assumptions are expensive. This skill requires every non-obvious implementation decision to be traceable to an authoritative source: the spec, the RFC, the official documentation, the ticket. Without a source, it's a guess.

When to Use

• When implementing a standard or protocol (OAuth, HTTP, JWT, etc.)
• When integrating with a third-party API
• When the implementation relies on undocumented behavior
• When "I think this is how it works" appears in your reasoning

Process

Step 1: Identify what you're implementing

What standard, protocol, API, or requirement are you implementing? What is the authoritative source?

Step 2: Read the source before writing code

For protocols: read the RFC. For APIs: read the official API documentation (not a blog post). For requirements: re-read the spec.

Step 3: Cite the source in the implementation

For non-obvious behavior: add a comment citing the source. Example:

# Per RFC 7519 Section 4.1.4, exp claim is NumericDate (seconds since epoch)
# https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.4

Step 4: Identify the gaps

What does the source not specify? These are places where you must make explicit decisions. Document them as decisions, not silently.

Step 5: Validate against the source

After implementation: validate your implementation against the authoritative source. For protocols: test against a reference implementation.

Verification Requirements

• Authoritative source identified and read before implementation
• Non-obvious behavior cites the source
• Gaps from the source documented as explicit decisions
• Implementation validated against the source