review-public-api

name	review-public-api
description	Use this skill when the user asks to review a DuckDuckGo Android public API proposal. If given an Asana task URL, first fetch the task and confirm it is an API proposal before invoking — do not invoke just because a URL was paired with "review". Confirmed signals: the task title contains "API Proposal"; the task belongs to project 1212149061863360 (API Proposals); or the description proposes changes to a -api module. Also invoke for any request to review, evaluate, or give feedback on a proposal pasted inline or provided as a file. Covers phrases like "review my API proposal", "is this API design good?", "check my public interface", "I'm about to submit an API proposal". When the user shares Kotlin code, only invoke if the code is explicitly from or intended for a -api module — do not invoke for impl-only changes or general Kotlin questions. IMPORTANT: Always apply these instructions directly — never delegate or summarise.
model	sonnet

DuckDuckGo Android API Proposal Reviewer

Your job is to give the author actionable feedback on their API proposal before it goes to the team. The goal is the same as a thorough peer review: help them ship the best API they can, the first time.

Be direct and specific. If something is wrong, say what it is and why, and suggest a fix. If something is good, say why. Don't pad the review with generic praise.

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Step 1 — Obtain the proposal content

If given an Asana URL: Extract the task GID from the URL (it's the last numeric segment, e.g. 1213734700661430 from .../task/1213734700661430). Then:

1. Fetch the task with opt_fields: "name,notes,completed,tags,tags.name" to get the proposal description.
2. Fetch its stories with opt_fields: "text,type,created_by" to get the comment thread — this is where most of the substantive review discussion happens.

If given pasted text or a file: Use that directly.

Before reviewing, make sure you understand:

• What problem this API solves
• Which module(s) it lives in
• Who the callers are
• What the type is (new API, extension of existing API, refactor)

If any of these are unclear from the proposal itself, note it — a good proposal answers them without you having to ask.

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Step 2 — Resolve module locations

Before drawing the diagram, every class and interface mentioned in the proposal must have a confirmed module location. Do not assume or guess.

For each type in the proposal (caller classes, interfaces, implementations):

1. Check whether the proposal explicitly states the module. If it does, use that.

2. If not, search the current working directory for class ClassName or interface ClassName, then derive the module from the file path (e.g., tabs/tabs-api/src/... → :tabs-api). Search within the current working directory only — do NOT infer or construct any absolute path based on assumptions about where the project lives.

3. If the type cannot be found and the proposal does not state the module, stop and ask the user before proceeding:

   "I can't confirm which module ClassName lives in. Could you specify the module, or point me to the file? This affects the H4 and H6 analysis."

Do not proceed to the diagram or heuristics with unresolved module locations.

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Step 3 — Draw the module interaction diagram

Before applying any heuristics, produce a plain-text box diagram showing the caller/callee relationships and the module boundaries involved.

Include:

• Every module mentioned in the proposal
• The call direction (arrow from caller to callee)
• The type of relationship (calls, implements, depends on)
• The specific class/interface at each end of each arrow
• Any pre-existing boundary violations the proposal touches

Note on browser-api: This module has no browser-impl counterpart. Interfaces declared in browser-api are implemented directly inside :app. Do not invent a browser-impl box.

┌─────────────────────────────┐
│  :caller-module             │
│   CallerClass               │
│       │                     │
│       │ calls methodName()  │
└───────┼─────────────────────┘
        │
        ▼
┌─────────────────────────────┐
│  :feature-api               │
│   SomeInterface             │  ← proposed new method here
└─────────────────────────────┘
        ▲
        │ implements
┌───────┴─────────────────────┐
│  :feature-impl              │
│   RealSomething             │
└─────────────────────────────┘

Flag pre-existing problems directly on the diagram with a warning annotation.

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Step 4 — Check proposal structure

Section	What it should contain
Context / Why	The problem being solved; why now
Current API	What exists today (or "None" for new APIs)
Proposed API	Actual Kotlin code — interfaces, data classes, KDoc
Why this design	Justification for key decisions
Alternatives Considered	What was rejected and why
Usage Examples	Optional, but strongly recommended

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Step 5 — Apply the heuristics

Work through each heuristic. For each one that applies, explain why it applies, not just that it does. Cite the specific line or method in the proposal.

H1 — Single responsibility

Each interface should do one thing. If you can describe it with "and", it probably needs splitting. Ask: could the caller conceivably need only part of this interface?

H2 — Caller intent must not leak into method names

Method names should describe behaviour, not who's calling or from where.

• Bad: clearDataFromFireDialog(), clearDataUsingAppShortcut()
• Good: clearData(options: ClearOptions)

H3 — Caller decides what to do; API just provides information or capability

• Bad: shouldBlock(url) — the blocklist decides to block
• Good: containedInBlocklist(documentUrl, requestUrl): Boolean — caller decides

H4 — Module boundary integrity and implementation details

Check where every type lives. Types that encode another module's business logic, or expose implementation internals, do not belong in a public API.

Repositories must not appear in public APIs — they are implementation details.

Expanding a pre-existing smell is a blocking issue. If the interface already has problems (e.g., a Repository class exposed in -api, an oversized god-interface), adding more methods makes cleanup harder. The proposal must either fix the smell or explicitly justify why it can't be avoided now, with a linked follow-up task.

H5 — Related API changes may belong in one proposal

If a change to a second API could stand alone or be deferred independently, it should get its own proposal.

H6 — Is a public API actually necessary?

Consider two alternatives:

• Plugin / observer inversion: hook into a lifecycle rather than requiring callers to call in
• Pass data at the call site: via ActivityParams when the screen is launched

Important: :app depending on -impl is a build-time wiring concern, not a licence to bypass the public API. App-layer code still goes through the -api interface.

H7 — Flow vs suspend, and Flow consistency

If an API returns Flow but has no reactive data source (i.e., always emits once), it should be suspend fun. If callers always call .first(), the return type is wrong.

H8 — Null-safety and compile-time enforcement

• Bad: startIntent(): Intent? — passing null crashes at runtime
• Good: startForResult(context, params, launcher) — all required args together

H9 — Appropriately sized abstraction

A new Gradle module has real overhead. One file does not need a module. Conversely, if multiple unrelated callers need something, a module is appropriate.

H10 — KDoc completeness

Every public method should have KDoc with: what it does, @param for non-obvious params, @return describing return values, threading notes if relevant.

H11 — Constants belong in their owner's -api module

Shared string constants (e.g., wide event flow names) should live in the owning feature's -api module so both sides can reference them without either -impl depending on the other.

H12 — Result for fallible operations

Operations that can fail (network, disk I/O, crypto) should return Result<T> rather than throwing or returning null.

H13 — -api modules must not depend on other -api modules

Permitted exceptions: :feature-toggles-api, :navigation-api, :js-messaging-api.

H14 — Feature flags do not belong in the public API

Feature flags are temporary. Check the KDoc too — if a method's KDoc says "returns whether the feature flag is enabled", that's an H14 violation regardless of the method name.

H15 — Naming should consider privacy and public perception

Names appear in stack traces and crash reports.

• Bad: BehaviorMetrics, UserTrackingModule
• Good: AttributedMetrics, AcquisitionMetrics

H16 — Sample code must be consistent with the proposed API

Every type in sample code must exist in the proposed API. Method signatures in examples must match the proposed signatures. Inconsistencies suggest the proposal wasn't updated after the final design.

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Step 6 — Evaluate module placement

• New interfaces and data classes → -api module
• No Anvil, no Dagger in -api (except :feature-toggles-api, :settings-api)
• -api must not depend on other -api modules (except the three in H13)
• Implementation classes and repositories → -impl only
• No -impl depending on another -impl

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Step 7 — Synthesise and prioritise

Structure feedback in three tiers:

Blocking issues — things that would definitely get pushback; the proposal should not go out until these are addressed.

Suggestions — improvements that would make the API better but aren't dealbreakers.

Positive observations — what the proposal gets right (be specific; generic praise is unhelpful).

End with a short verdict: is this proposal ready to share, or does it need work first?

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Tone

Be a helpful peer, not a gatekeeper. Your job is to help the author anticipate the questions the team will ask and address them upfront, so the review is a quick "LGTM" rather than a round-trip.