Use a design document to explain a proposed implementation and invite feedback, an internal RFC when a defined group should review a proposal before a decision, and an ADR to record a consequential architectural choice and why it was made. These documents serve different stages of a decision, so teams often link a proposal or RFC to a concise ADR rather than treating the formats as alternatives.
What each document is for
Design document: explain a proposal
A design document describes a proposed implementation in enough detail for others to understand it and give feedback while it can still change. Google’s documentation best practices describe design docs as proposals written to collect feedback. A useful document covers the problem and goals, the proposed design, alternatives, impacts and risks, open questions, and—where relevant—reviewers and a feedback deadline.
After implementation, Google recommends treating the design document as an archive of decisions, not as a guarantee that it still describes the implementation in full. Keep the current implementation documentation accurate separately.
Internal RFC: invite structured review
In many engineering organizations, an internal RFC is a proposal circulated for comments before a choice is settled. The label does not define a universal company process: teams decide who reviews, how feedback is collected, and who has authority to resolve disagreement. Make those details explicit, along with the proposal’s scope, options, trade-offs, affected teams, feedback process, and final disposition.
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ADR: preserve a decision
An architectural decision record captures a significant choice, the context that led to it, and its consequences or trade-offs. AWS describes an ADR in those terms in its ADR process guidance. Google Cloud’s ADR overview recommends recording decisions when engineering options must be evaluated and the selection and reasoning should be preserved.
An ADR is most useful when future maintainers may need to understand why the architecture took a particular shape, what alternatives were considered, or which constraints influenced the choice. Include the decision’s status and date, and link to the proposal or review discussion for detail.
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Compare them by purpose, timing, and audience
| Document | Primary purpose | Typical timing | Audience | What it should leave clear |
|---|---|---|---|---|
| Design document | Explain and improve a proposed implementation | Before implementation, while design can change | Implementers and reviewers | Problem, goals, proposed approach, alternatives, risks, and open questions |
| Internal RFC | Solicit structured comments on a proposal | Before the decision | Defined reviewers and affected teams | Scope, options, review process, decision owner, and how comments will be resolved |
| ADR | Record a significant architectural choice and its rationale | When a decision is made; later records can capture changes | Future maintainers and people affected by the decision | Context, selected option, consequences, status, and links to supporting material |
| IETF Internet-Draft / RFC process | Develop and publish Internet technical specifications or related documents | Through the relevant IETF process | Internet technical community | Applicable stream, review and approval path, and publication status |
The first three rows describe common engineering-document functions, not universal naming rules. A team can call its proposal an RFC or a design doc; what matters is whether the document makes the proposal, feedback process, decision authority, and final status unmistakable.
Choose the right document for the decision stage
- Decide whether the choice is consequential. If it affects system structure, quality attributes, or behavior—and a future team could otherwise repeat the debate or misunderstand a trade-off—plan to record it in an ADR. Keep routine implementation details out unless they materially affect the architectural rationale.
- Work out whether the choice is still open. If people need to shape the proposed implementation, write a design document. If your organization uses an RFC process for broad proposal review, use that mechanism and name the reviewers, decision owner, and feedback window.
- Record the outcome after the choice. Write an ADR that states what was selected, the context, and the consequences. Link the proposal and discussion, and update the decision record if review changed the original proposal.
- Preserve history if the decision changes. Keep the earlier ADR as a record of what was decided at the time, and create a new one that supersedes it. Explain the changed constraints or evidence. AWS’s ADR guidance describes accepted records as immutable and a later accepted ADR as the way to supersede an earlier one.
When to use both a proposal and an ADR
Use a design document or internal RFC to explore options and gather feedback; use an ADR to preserve the final decision. Link the records so the ADR stays concise while readers can follow the fuller analysis and discussion. If the choice changes during review, make the ADR reflect the decision actually made—not merely the proposal’s original recommendation.
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This combination is especially useful when the proposal needs substantial discussion but the lasting record should be easy to scan. A proposal can evolve during review; the ADR should make the selected option and its rationale easy to find later.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.“RFC” can mean an Internet publication, not an internal proposal
In Internet standards work, RFC means a document published in the RFC Series. The series includes multiple streams and statuses, and publication as an RFC does not by itself make a document an Internet Standard. The RFC Editor’s series overview explains the streams and status distinctions.
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An Internet-Draft is a working document, not a published RFC. The RFC Editor’s explanation of how RFCs are created notes that publishing an Internet-Draft does not mean it has been approved or will eventually become an RFC. For a specific RFC, check its current metadata, stream, status, and any related updates or obsoletions rather than inferring standards status from its number.
Therefore, if someone asks for an “RFC” at work, clarify whether they mean the company’s proposal-review format or an Internet standards document. An internal template is not a substitute for the IETF process.
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What to put in each record
- Design document: problem, goals, proposed implementation, alternatives, impact, risks, open questions, reviewers, and any feedback deadline your team uses.
- Internal RFC: proposal and scope, options and trade-offs, affected teams, review and feedback process, decision owner, and the eventual disposition.
- ADR: context, decision, consequences or trade-offs, status, date, and links to the proposal, discussion, and relevant implementation material.
These contents are practical guidance rather than mandatory industry-wide templates. Choose a structure that helps your intended readers find the information they need, and state clearly whether the document is a proposal, a record of a decision, or both.
Quick Recap
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