Engineers ignore specs that force them to guess. A spec gets read and built from when it defines exact behavior for every input, names every field and state involved, and clearly separates decided requirements from open questions — so no one has to interrupt their work to ask what you meant.
Quick answer: Specs get skipped when engineers can't extract a concrete decision from them on the first read. Write for the person about to write code: state behavior precisely, use tables for acceptance criteria, and label open questions instead of burying them in prose.
Why Engineers Stop Reading Specs (Even Good Ones)
Engineers stop reading specs when the document makes them do translation work — parsing narrative prose to find the one sentence that actually constrains the code. Every paragraph they have to re-read to locate a decision trains them to skim the next one, and eventually to skip the document entirely and just ask in Slack.
This isn't an engineering-culture problem, and it isn't laziness. The Standish Group's long-running CHAOS Report has, across multiple survey cycles, placed incomplete or unclear requirements among the top handful of reasons software projects run over budget, slip their timeline, or get cancelled outright — well ahead of raw technical difficulty. The requirement was usually written down somewhere. It just wasn't written so it could be acted on without a follow-up conversation.
The cost compounds the later it's caught. Barry Boehm's foundational research on software economics found that the cost of fixing a misunderstood requirement climbs by roughly an order of magnitude at each stage it survives undetected — cheap to catch in a spec review, expensive once an engineer has already built, tested, and shipped the wrong thing. A spec that gets skimmed instead of read is a spec that defers that cost to the worst possible moment: after the pull request.
In practice, the skim happens because of a handful of recurring patterns:
- Vague verbs — "handle," "support," "manage" — that describe an intention without specifying a behavior.
- Missing states — the happy path is described in detail; empty states, error states, and permission edge cases are left implicit.
- Buried decisions — the one sentence that actually resolves an ambiguity is on paragraph four, indistinguishable in weight from the throat-clearing around it.
- No linked artifact — a layout or flow is described in prose instead of shown, leaving the engineer to reconstruct a picture from adjectives.
- No priority or status markers — everything reads as equally final, so engineers can't tell a locked decision from a PM thinking out loud.
This article stays narrowly focused on fixing that pattern. For the broader discipline of structuring a PRD end to end — problem framing, scoping, and rollout, not just the writing itself — our PRD writing masterclass for the AI era covers that ground in full.
What "Written for Engineers" Actually Means
Writing for engineers means replacing narrative description with verifiable statements — each requirement specific enough that two engineers, reading it independently, would build identical behavior. That's the practical test: could someone implement this without messaging you first?
This isn't a new idea invented for software teams. The IEEE/ISO/IEC 29148 requirements-engineering standard, which formalizes decades of systems-engineering practice, defines a good requirement as verifiable — there must exist some inspection, test, or demonstration that proves it was met. A requirement you can't test is a requirement you can't finish; it just stays "kind of done" forever, which is exactly the ambiguity engineers learn to route around.
Most vague PM language fails that test not because the PM was careless, but because natural language is genuinely bad at specifying exact behavior — it's built for persuasion and narrative, not for constraint-setting. The fix is almost mechanical: replace the adjective with the threshold, the verb with the state transition, and the description with the number.
| Vague (reads fine, specifies nothing) | Engineer-ready (verifiable) |
|---|---|
| "The system should handle large files gracefully" | "Files over 25 MB show a progress indicator. Files over 200 MB are rejected with error code FILE_TOO_LARGE and the message shown in the mock." |
| "Should be fast" | "The search results panel renders within 300 ms of keystroke for queries under 50 results, measured at p95." |
| "Support most browsers" | "Fully supported: Chrome, Edge, Safari (last two major versions). Degraded but functional: Firefox. Unsupported: IE11 — shows the existing upgrade banner." |
| "Notify the user" | "An in-app toast fires on success; an email fires only if the user is offline for more than 5 minutes, per the existing notification-preference logic." |
| "Similar to the mobile app" | Link the exact screen and flow, or write the three behaviors that must match — "similar" is not a spec, it's a pointer to a spec that doesn't exist yet. |
Read the table as a translation exercise: every left-column phrase is a genuine sentence a PM would write and genuinely believe is clear. The right column shows what an engineer actually needs to stop guessing — a threshold, an enum, a number, or a named exception.
Prose also can't fully specify a layout, a flow, or a state diagram, no matter how carefully it's written. Pair every UI-affecting requirement with an actual artifact instead of a paragraph describing one; our PM's guide to responsive wireframing covers building the clickable reference an engineer can point to instead of interpreting your adjectives.
Anatomy of a Spec Fragment Engineers Can Build From
A spec engineers can build from separates five things: the context, the user-facing behavior, the data and states involved, the acceptance criteria, and the open questions — each labeled and separated, so an engineer can jump straight to the part relevant to what they're building right now instead of reading top to bottom.
Below is a real fragment, not a description of one — the format you'd actually paste into a spec for a mid-sized feature.
Example: a spec fragment for "Bulk Archive Conversations"
Context
Support leads currently archive conversations one at a time from the inbox. Power users with 200+ resolved conversations in a queue want to select many and archive them in a single action. Ships behind the existing inbox_bulk_actions flag.
User-facing behavior
- A checkbox appears on each conversation row when the inbox enters "select mode."
- Selecting one or more rows reveals a persistent action bar with an "Archive selected" button.
- Clicking "Archive selected" archives every selected conversation and shows a confirmation toast with an "Undo" action, active for 10 seconds.
Data and states involved
conversation.statusmoves fromopenorresolvedtoarchived.conversation.archived_atandconversation.archived_byare set on archive, cleared on undo.- Archiving is reversible via
Undoonly inside the 10-second window; after that, agents use the existing single-item "Unarchive" action.
Non-goals
- Bulk unarchive is out of scope for this release.
- No bulk action beyond archive — no bulk delete, no bulk assign — ships in this iteration.
Notice what this fragment does that a paragraph version wouldn't: it names the exact fields that change, states a numeric threshold (10 seconds) instead of "briefly," and explicitly rules out two things an engineer might otherwise reasonably assume were in scope. That last part — the non-goals — prevents more rework than almost anything else in a spec.
Writing Acceptance Criteria That Remove Ambiguity
Acceptance criteria remove ambiguity when they're written as testable conditions, not restated features. The Given/When/Then format, borrowed from behavior-driven development, forces you to specify a starting state, a trigger, and an exact observable outcome for every case — including the edge cases a narrative description quietly skips.
Continuing the bulk-archive example, here's what that looks like as a full acceptance-criteria table, including the failure modes a first draft usually omits:
| ID | Given | When | Then |
|---|---|---|---|
| AC-1 | Select mode is on, 0 conversations selected | User clicks "Archive selected" | Button is disabled; no action bar appears |
| AC-2 | 12 conversations selected, all open or resolved | User clicks "Archive selected" and confirms | All 12 move to archived, archived_at/archived_by set, toast reads "12 conversations archived" with Undo |
| AC-3 | A batch was just archived, under 10 seconds ago | User clicks Undo | All conversations in that batch revert to prior status; archived_at/archived_by clear |
| AC-4 | The 10-second Undo window has elapsed | User looks for Undo | Toast has dismissed; Undo unavailable — user must unarchive individually |
| AC-5 | One selected conversation was deleted by another agent mid-selection | User clicks "Archive selected" | That conversation is skipped; the rest archive normally; toast reports "11 of 12 archived — 1 no longer exists" |
| AC-6 | User lacks archive permission on one selected conversation (shared queue) | User clicks "Archive selected" | Permitted conversations archive; the unauthorized one is skipped; toast names the skipped count |
| AC-7 | User selects 500 conversations (batch limit is 200) | User clicks "Archive selected" | Validation message appears before submission: "Select 200 or fewer conversations at a time" |
Rows AC-5 through AC-7 are the ones a rushed first draft leaves out — and the ones that generate a Slack thread mid-sprint when an engineer hits them without a written answer. Writing them down before code starts is strictly cheaper than answering them live while someone's blocked.
When acceptance criteria hinge on how data is shaped — new fields, status enums, relationships between records — define that shape once, in one place, instead of repeating field definitions inside every row. Our PM's guide to reviewing a data model covers documenting that layer clearly, so engineers aren't reverse-engineering your schema from scattered mentions across the spec.
Open Questions, Edge Cases, and Non-Goals: The Sections That Prevent Rework
An Open Questions section prevents rework by making unresolved decisions visible instead of implicit. Every question you don't write down gets answered anyway — just silently, by whichever engineer hits it first — and their answer may not match what you'd have chosen, or what your designer already assumed.
Two practices from outside product management back this up directly:
- Amazon's "working backwards" PR/FAQ process, documented extensively by former Amazon executives including Colin Bryar and Bill Carr, requires writers to draft the FAQ section before a launch is approved — forcing every hard, unresolved question into the open early, rather than letting it surface as a surprise during build.
- Google's internal "design docs" convention, described publicly by engineers including Malte Ubl, standardizes an "Alternatives Considered" and "Non-Goals" section in every design doc — the explicit acknowledgment that scoping out is as important a decision as scoping in, and worth writing down for the same reason.
A usable Open Questions section needs three things per row, not just a question mark: the question itself, an owner, and a status.
| Question | Owner | Status |
|---|---|---|
| Does "Undo" need to work if the user navigates away and back within 10 seconds? | PM | Open |
| Should the 200-item batch limit be configurable per workspace tier? | PM + Eng lead | Open |
| Do we log bulk-archive as one audit event or one per conversation? | Eng | Resolved — one event, with a conversation_ids array |
A question with no owner is a question nobody's actually accountable for closing, and it will still be open at code freeze. A question with no status forces every reader to re-derive whether it's still blocking or already settled — exactly the re-reading tax this whole article is about eliminating.
Keeping the Spec Alive as the Build Progresses
A spec stops getting read the moment it stops matching reality. Once engineers discover the document lags behind decisions made in stand-up or in a Slack thread, they stop trusting it as the source of truth — and route around it entirely, which defeats the entire point of writing one in the first place.
The fix isn't writing a more exhaustive spec upfront; requirements will change as engineering surfaces constraints you didn't know about. The fix is treating the spec as a living document with visible version history, not a PDF frozen at kickoff.
Every resolved open question should get folded back into the requirements it affects, in the same document — not left stranded in a chat thread only the people in that channel can find. This is the exact discipline behind writing a living PRD that stays current instead of decaying the moment the kickoff meeting ends.
This is also, concretely, the discipline Prodinja's Spec Studio is designed around: it lets you keep requirements, acceptance criteria, and open questions in one living PRD you can edit and version as the spec evolves — so the artifact an engineer opens mid-sprint can reflect the same decisions as the one you wrote at kickoff, instead of a stale snapshot from three weeks earlier.
Key Takeaways
- Vague verbs are the root cause, not sloppy writing — "handle," "support," and "manage" describe intent, not behavior; replace each with a threshold, an enum, or a numbered exception.
- Acceptance criteria should be testable conditions, not restated features — use
Given/When/Thenand deliberately include failure and edge-case rows, not just the happy path. - A Non-Goals section prevents more rework than almost any other line in a spec — stating what's explicitly out of scope stops engineers from reasonably assuming it's in.
- Open questions need an owner and a status, not just a question mark — an unowned question stays open silently until someone hits it mid-build.
- Pair prose with an actual artifact wherever behavior is visual — a linked wireframe or flow removes an entire category of misread requirements that no amount of careful adjective choice fixes.
- A spec that goes stale trains engineers to stop trusting it — version it and keep it current, or expect the team to route decisions around it in Slack instead.
Frequently Asked Questions
How long should a spec be?
Long enough to remove ambiguity for the specific feature, no longer — there's no fixed page count. A three-field toggle might need half a page; a bulk-action feature with permission edge cases might need two pages of acceptance criteria alone. Length should track the number of decisions being made, not the perceived importance of the feature.
What's the difference between a PRD and an engineering spec?
A PRD typically covers the problem, the user, the business case, and the scope at a product level; an engineering spec (or the technical section within a PRD) drills into exact behavior, states, data, and acceptance criteria an engineer builds against. Many teams merge both into one living document rather than maintaining two separately, which is the pattern this article assumes.
Should PMs write acceptance criteria, or should engineers?
PMs should draft the first pass — they own the intended behavior and the edge cases that matter to the user — then have engineers review and add technical edge cases the PM wouldn't think to specify, like race conditions or failure modes. Written collaboratively, acceptance criteria catch far more than either role would alone.
How detailed should acceptance criteria be for a small feature?
Even a small feature needs at least one row per meaningful state: success, empty, error, and permission-denied, at minimum. Skipping the "small" ones is exactly how a two-line feature turns into a mid-sprint Slack thread — size of the feature doesn't reduce the number of states it can be in.
Is Given/When/Then the best format for acceptance criteria, or should I just use a checklist?
Given/When/Then is worth the extra structure whenever a requirement depends on a starting state or has more than one possible outcome — most real features. A flat checklist works fine for simple, state-independent requirements ("the button uses the primary color token") where there's nothing to vary.