How to Write Technical Specs That People Actually Read

A practical guide for PMs and engineering leads who need to write specs that prevent wasted engineering effort, align stakeholders, and survive contact with reality.

Why Specs Fail

Most technical specs fail for one of these reasons:

The Spec Spectrum

Different decisions need different levels of documentation:

The most common mistake is using the wrong level. A 15-page RFC for a 2-day feature wastes everyone's time. A 2-sentence Slack message for a new service wastes engineering time when it's built wrong.

Writing Process

Step 1: Start with the Problem (15 minutes)

Before opening a template, answer these questions in plain language:

1. What's broken or missing?

2. Who cares? (users, internal teams, the business)

3. What happens if we do nothing?

4. What does success look like?

If you can't answer these clearly, you're not ready to write a spec.

Step 2: Sketch the Solution (30 minutes)

Draw the architecture on a whiteboard or in a text file. Don't worry about formatting. Focus on:

• What are the main components?
• How do they talk to each other?
• Where does data live?
• What's the happy path?
• What can go wrong?

Step 3: Identify Your Audience (5 minutes)

Step 4: Write the Spec (1-3 hours)

Use a template from templates/. Fill in the sections that matter, skip the ones that don't. Every section you include should earn its place.

Step 5: Get Feedback (1-3 days)

1. Share the draft with 2-3 reviewers

2. Give them a deadline (3 business days is reasonable)

3. Ask them to focus on: "Is this the right approach?" not "Are there typos?"

4. Use the design review checklist from templates/design-review-checklist.md

Writing Tips

Be Specific

Address Risks Honestly

Don't hide risks to make the spec look cleaner. A spec that says "there are no significant risks" is either dishonest or hasn't been thought through.

Bad: "This approach has minimal risk."

Good: "The main risk is data migration. If the migration fails mid-way, we'll have inconsistent data between the old and new tables. Mitigation: we'll run the migration behind a feature flag, writing to both tables during the transition period, and validate consistency before cutting over."

Include Diagrams

A single architecture diagram replaces 500 words of description. ASCII diagrams in markdown are perfectly acceptable:

Client → API Gateway → Service A → Database
                    ↘ Service B → Cache → Database

Write for the Future Reader

In 6 months, someone (maybe you) will read this spec to understand why a decision was made. Include the context that won't be obvious later:

• Why did you choose Option A over Option B?
• What constraints existed at the time? (team size, timeline, existing infrastructure)
• What would you do differently if you had more time/resources?

Spec Review Best Practices

As a Reviewer

1. Read the whole thing first before commenting. Your first concern might be addressed later in the document.

2. Focus on the approach, not the details. "Is this the right architecture?" matters more than "Should this be a POST or PUT?"

3. Distinguish blocking concerns from suggestions. Use labels: [blocking], [suggestion], [question].

4. Propose alternatives, don't just criticize. "This won't scale because X. Consider Y instead."

5. Timebox your review. If you've spent 2 hours reviewing a 5-page spec, you're over-thinking it.

As an Author

1. Don't take feedback personally. The spec is a tool, not your identity.

2. Respond to every piece of feedback. Even if the answer is "considered and declined because X."

3. Update the spec based on feedback. Don't leave the final version in the comments.

4. Know when to stop. A spec that's 90% right and shared beats a spec that's 100% right and stuck in draft.

ADR Best Practices

Architecture Decision Records deserve special attention because they're the only document that explains *why* your system is the way it is.

When to Write an ADR

Write an ADR when:

• The decision is hard to reverse (database choice, API versioning strategy)
• Multiple viable options exist and people disagree
• The decision affects multiple teams
• Future developers will wonder "why did we do it this way?"

ADR Numbering

Use sequential numbers: ADR-001, ADR-002, etc. Never reuse numbers. If an ADR is superseded, mark it as "Superseded by ADR-XXX" but keep it in the repository.

Keep ADRs Short

A good ADR is 1-2 pages. If it's longer, you're writing a design doc, not a decision record. The ADR captures the decision and rationale; the design doc captures the implementation details.

Technical Spec Templates

By PM Toolkit Pro | $25

A complete set of templates for writing technical specifications, architecture decision records, RFC proposals, and API designs. Built for technical PMs and engineering leads who need to document decisions clearly and get alignment before writing code.