Feature Discovery

Feature discovery

Feature-discovery traces how an existing feature, module, or behavior works and reports it in chat, evidence-cited: another engineer comes away knowing what it is, how it works, where it is used, and what remains uncertain.

Inputs

Intake may be structured — Projects Affected: plus a What: block — or free-form; infer the projects and topic. Questions are for blocking clarifications only; user away → state the assumption and continue best-effort.

Rules

• Read-only, chat-only. Do not edit code, config, docs, native memory, ADRs, prompts, issues, or generated artifacts while discovering — CONTEXT.md and artifact edits wait for step 6 approval. Never create docs/discovery/ files, and do not read legacy discovery files unless the user names one — they go stale. No git fetch, git pull, installs, migrations, or destructive commands.
• Code is the source of truth when evidence conflicts with prose docs, issues, or comments. Cite evidence for every claim (Evidence style below); separate confirmed facts from inference; never invent rationale. The tell: a comment, issue, or native memory outranking the code it describes.
• If graphify-out/graph.json exists (project root, else workspace root), query it before raw search; older than ~7 days → suggest graphify update .; missing → skip graphify. Scope with graphify query/path/explain before broad rg sweeps. Verify graph answers against current code and flag staleness — never run graphify update . yourself; discovery stays read-only. Do not hunt for a graph elsewhere or suggest installing it.
• Trace behavior, not just symbols. Follow definitions to callers and user-facing flows from entry points down; flag seam-reuse when similar behavior exists in multiple paths. The tell: a symbol dump with no usage site or user-visible effect.
• Keep scope thin. Broad intake gets split; discover the first slice before expanding. Near ~120K tokens with core unknowns unresolved, stop and recommend a scope split or handoff. The tell: drifting into product discovery or experiment design without an explicit pivot.
• Stop after presenting the report. Suggest the next skill; never invoke it or start implementation without a fresh request. Grillable unknowns stay as open decisions for /feature-prompt or /grill-with-docs; ungrillable ones ("needs to feel/see it") route to /handoff + /prototype (when installed; else state the uncertainty plainly). Destination or open questions still foggy → suggest /wayfinder, not /feature-prompt; a PR-sized prompt cannot be written through fog.
• Emit Stage / Found / Next / Needs user at each phase transition — one line per field. Phases: parsed, discovered, validated, report.
• Sub-agents: dispatch local lanes automatically for independent work — never cloud agents; announce the lane count at dispatch and report each lane as it completes. Summaries back, not transcripts; synthesis stays in the main session.

Workflow

1. Parse and locate

Map project codes to git roots and package boundaries via repo names, package metadata, or READMEs; unmappable → say so early, continue best-effort.

2. Discover the topic

Search exact terms from What, then likely aliases, routes, components, API paths, config keys, env vars, tables, filenames, and test names — across code, tests, docs, configs, migrations, jobs, and feature flags; rg first; prefer CLI over MCP for codebase evidence. Critical dependency internals with thin local evidence → optionally fetch targeted dependency source (opensrc, when installed), minimal scope, cited concretely. Git history only when code scanning does not explain the topic, and only the last 2 months — why or when behavior changed, never primary truth.

3. Read issues bounded, or not at all

Mine context for issue references — the conversation, AGENTS.md, /CONTEXT.md, ADRs under specs/adr/, local docs, issue caches. A bounded issue set → read every issue with comments (default gh issue view --comments; a workspace-named tracker and its mapping override the command); reliable labels or exact terms → bounded search, reading every plausible match. If context cannot bound the search, pause and ask the user to approve a broad issue-tracker scan first — explain that it can take a long time. Not granted, or user away → continue with code, docs, tests, and history, stating that broad scanning was skipped.

Resolve `: the *.code-workspace directory if one exists, else the per-context root (CONTEXT-MAP.md` at repo root), else the repo root.

4. Track candidate context terms

Compare discovered domain terms with CONTEXT.md — at `, else nearby project docs — and flag missing, stale, renamed, overloaded, or ambiguous ones. What qualifies, presentation, the away-fallback, and applying approvals live in [references/context-terms.md`](references/context-terms.md).

5. Validate twice

Pass 1: cross-check the explanation against code, tests, docs, configs, and any issues or history used. Pass 2: repeat with aliases and reverse lookups, hunting contradictory code paths and stale assumptions; tighten or downgrade claims. Validate candidate terms against the strongest code evidence, sweep the tells in Rules, and mark dead code, unclear ownership, missing tests, contradictions, and skipped scans.

6. Present the report and stop

For CONTEXT.md or other artifact updates after the report: show each target path, proposed text, and reason; wait for explicit approval, then follow Applying approved updates in references/context-terms.md (away-fallback: no reply → no edits; candidates stay in the report).

Output

Use this structure exactly: ≤3 bullets per section; keep the whole report under ~500 words unless the trace spans multiple projects. For a trivially small question (one symbol, config key, or route), say Quick trace up front and emit only sections 1–3 and 8, marking the rest N/A — never shrink a genuine multi-project discovery this way.

# Feature discovery: [Topic]

## 1. Summary
- [What this is, where it lives, main finding, key caveat.]

## 2. What it does
- [Behavior in product/domain terms: inputs, outputs, side effects, project(s).]

## 3. How it works
- [Flow; key files, functions, routes, configs, jobs; conditions, flags, error paths.]

## 4. Where it is used
- [Usage sites with file references; tests/docs/configs confirming usage.]

## 5. Why it was needed / context
- [From conversation, docs, comments, issues, or recent commits — or: "No reliable rationale found in context, docs, comments, or recent history."]

## 6. Candidate CONTEXT.md terms
- [`Term` — suggested action; short description; evidence; why it matters. Stale context → quote current wording beside the contradicting code.]
- [End with: "Reply with the term names to approve, wording changes, `approve all`, or `skip context updates`." If none: "No candidate CONTEXT.md term updates found."]

## 7. Risks, gaps, and recommended next checks
- [Risk (user-value, feasibility, data, security, operational), dead code, missing test, or unclear owner; next check; what could not be verified.]

## 8. Validation performed
- [Checks run in each pass, commands named; anything skipped stated, including the broad-issue-scan outcome (approved, bounded, skipped, or unavailable) and which issues were read or excluded.]

## 9. Suggested next skills (optional)
- [/skill-name: reason tied to this report. 1–3 items, adjacent workflow steps.]

Evidence style. Cite file:line (or file plus symbol) with its role; issues as #123, commits as short hash plus date. For quoted command output, quote the shortest decisive tail — the pass/fail line and counts — and name the rest.

Completion criteria

• [ ] Every factual claim in sections 1–8 carries a citation per Evidence style
• [ ] git status shows no files created or modified by this discovery (approved step-6 CONTEXT.md updates excepted)
• [ ] All nine sections in order — or Quick trace declared, with sections 1–3 and 8 and the rest N/A
• [ ] Section 6 ends with the four-option approval ask, or the no-candidates line
• [ ] Session stopped after the report — no skill invoked, no implementation started

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: devarfeen
• Source: devarfeen/agent-skills-kit
• License: MIT

Install and usage instructions live in the source repository linked above.