| name | gdd-router |
| description | Routes a /gdd command to fast|quick|full path + S|M|L|XL complexity_class and returns {path, complexity_class, model_tier_overrides, resolved_models, estimated_cost_usd, cache_hits}. A SKILL.md prompt the model executes to emit a routing-decision JSON from rule tables (no separate agent spawn). Optional/advisory - invoked only by the skills that opt into routing; the budget-enforcer hook tolerates its absence. Read by hooks/budget-enforcer.ts. |
| argument-hint | <intent-string> [<target-artifacts-csv>] |
| tools | Read, Bash, Grep |
gdd-router
Role
You are a deterministic routing skill. You do not spawn agents. You read .design/budget.json, reference/model-prices.md, .design/cache-manifest.json (if present), and the agent frontmatter list, then emit a single JSON object describing the planned spawn graph. The budget-enforcer hook (hooks/budget-enforcer.ts) consumes your output on every Agent tool call.
Invocation Contract
- Input:
intent-string (e.g., "run discover stage on greenfield project") + optional comma-separated list of target artifacts (files this command will touch).
- Output: a single JSON object to stdout - nothing else on the line, no prose wrapper:
{
"path": "fast",
"complexity_class": "M",
"model_tier_overrides": {"design-verifier": "haiku"},
"resolved_models": {
"design-reflector": "gpt-5",
"design-context-checker": "gpt-5-nano",
"design-verifier": "gpt-5-nano"
},
"estimated_cost_usd": 0.034,
"cache_hits": ["design-context-builder:abc123"]
}
path enum: fast (single Haiku + no checkers), quick (Sonnet mappers + Haiku verify), full (Opus planners + full quality gates). Stays unchanged for back-compat per D-05.complexity_class enum: S | M | L | XL (Phase 25 / D-04, D-05). Additive to path - existing consumers reading only path keep working. Mapping is documented in the Path Selection Heuristic table below.model_tier_overrides merges agent frontmatter default-tier with .design/budget.json.tier_overrides - budget.json wins per D-04. Enum stays opus|sonnet|haiku for back-compat across all 14 runtimes; consumers that need the concrete model name for the active runtime read resolved_models instead.resolved_models is a per-agent map of concrete model IDs for the runtime in use (Phase 26 / D-07). Keys are agent names; values are runtime-specific model strings (e.g. "gpt-5" under codex, "gemini-2.5-pro" under gemini, "claude-opus-4-7" under claude) or null when the resolver can supply no model (missing tier-map row, missing tier on the row). Additive to model_tier_overrides - existing consumers reading the tier-name map keep working unchanged; new consumers (budget-enforcer cost computation, cost telemetry, bandit posterior store) read resolved_models for runtime-correct cost. See Runtime-aware model resolution below for the computation contract.estimated_cost_usd is the sum of per-spawn estimates using the D-06 formula and reference/model-prices.md.cache_hits is a list of {agent}:{input-hash} strings that exist in .design/cache-manifest.json and are within TTL; emitting a hit lets the hook short-circuit that spawn per D-05.
Output schema versioning
The router output contract is additive across phases. The current shape (Phase 26, v1.26.0) carries:
| Field | Added in | Status |
|---|
path | v1.10.1 (10.1-01) | stable |
model_tier_overrides | v1.10.1 (10.1-01) | stable, enum unchanged |
estimated_cost_usd | v1.10.1 (10.1-01) | stable |
cache_hits | v1.10.1 (10.1-01) | stable |
complexity_class | v1.25.0 (25-02) | stable, additive |
resolved_models | v1.26.0 (26-04) | stable, additive |
Existing consumers reading any subset of the older fields keep working unchanged across these bumps - the schema is a strict superset at every phase boundary. New fields are documented inline in this skill rather than in a separate JSON-schema file (the SKILL is the contract - same convention Phase 25 followed for complexity_class).
Path Selection Heuristic
The router emits path (3-tier: fast|quick|full, legacy enum, stable for back-compat) AND complexity_class (4-tier: S|M|L|XL, Phase 25 / D-04 additive). Full mapping table, bucket-assignment signal list, --dry-run downgrade rule, and the S-class short-circuit semantics live in ./router-rules.md#path-selection-heuristic. The S-class short-circuit is essential: when complexity_class would be S, the router does not run; the deterministic skip list lives in the /gdd:* SKILL.md entry, and the budget-enforcer hook treats "no payload + matching command name" as the S signal.
Cost Estimation Algorithm
Standard cost-estimation pseudocode (sum over planned spawn graph; per-agent (in_tok / 1e6) * in_rate + (out_tok / 1e6) * out_rate using ./reference/model-prices.md) lives in ./router-rules.md#cost-estimation-algorithm.
Runtime-aware model resolution
Computation contract for resolved_models, implementation surfaces (scripts/lib/runtime-detect.cjs + scripts/lib/tier-resolver.cjs), per-agent emission rules (including the JSON-null contract), and the Claude-runtime back-compat assertion live in ./router-rules.md#runtime-aware-model-resolution. Top-line: model_tier_overrides keeps its opus|sonnet|haiku enum for back-compat; resolved_models runs the per-runtime translation additively on top.
Cache-Hit Detection
Delegate to skills/cache-manager/SKILL.md (Plan 10.1-02). The router lists candidate {agent}:{input-hash} tuples; the cache-manager confirms freshness against TTL from budget.json.cache_ttl_seconds.
Integration Point
The router is optional and advisory, not a universal first step. Only the handful of skills that explicitly opt into routing reference it (today: the root pipeline SKILL.md / /gdd:handoff, and /gdd:style documents that it deliberately does not invoke the router because it is a leaf invocation). The pipeline stage skills (explore / plan / design / verify) do not spawn the router. When a skill does invoke it, the flow is: invoke the router via Task or inline invocation; receive the JSON blob; pass it to downstream agents as context so the budget-enforcer hook has the router decision available in tool_input metadata when the first Agent spawn fires.
When no skill supplies a router decision, the budget-enforcer hook reads tool_input.context.router_decision as absent and falls back to its legacy back-compat path - the router's absence is tolerated by design, never an error.
Failure Modes
If .design/budget.json is missing, assume defaults from reference/config-schema.md per D-12. If reference/model-prices.md is missing, emit estimated_cost_usd: null and log a warning - do not block.
Emitting capability_gap on unmatched intent
When the router cannot resolve intent-string to a known agent (no description match, no default-tier rule, no path-selection fallback), emit ONE capability_gap event with source: "router" before returning the conservative-fallback JSON. Feeds Phase 29 Stage-0 telemetry - see ./capability-gap-emitter.md for the synchronous Node snippet, semantic notes (suggested_kind = "agent", MCP-probe exclusion per D-08, back-compat invariant on router output), and the opaque-extras payload routing through appendChainEvent.
Emitting router_pick on a resolved pick
When the router DID resolve a pick - it has the path/complexity_class/resolved_models decision and is about to return the decision JSON - emit ONE router_pick event (source: "router") recording which skill/agent was auto-picked, as the last step before returning. Side-effect only; the output JSON contract is UNCHANGED. Feeds the D-02 under-reached-skill instrument (Phase 33 baselines per-skill pick rates) - see ./router-pick-emitter.md for the synchronous Node snippet, the 7-field no-PII payload (context_hash only - never the raw prompt), and the opaque-extras routing through appendChainEvent.
Non-Goals
The router does not: (a) make a model call, (b) write files, (c) enforce budget caps (that's the hook's job), (d) learn from history (Phase 11 reflector territory per D-07).
The router does not author capability-gap CLUSTERS - Stage-0 emit is single-event-per-failure. Aggregation across events is Plan 29-03's reflector pass.
