fable-advisor

Spend Fable 5 tokens only where they change the outcome.

A Claude Code plugin that teaches an Opus orchestrator to consult Claude Fable 5 — Anthropic's most capable (and most expensive) model — the way you'd use a top-dollar consultant: rarely, at the right moment, with a well-prepared brief, for a terse verdict.

Day-to-day work runs on Opus. Fable gets called at inflection points: the decisions that are costly to revert once you start building. Everything else stays at Opus rates.

Why

Fable 5 is billed at $10 / $50 per MTok — exactly 2× Opus 4.8 ($5 / $25). Left undisciplined, an orchestrator either never uses it (leaving quality on the table) or uses it lazily — full-context dumps, chatty back-and-forth, delegating generation — which burns money for nothing.

The protocol is adapted from Anthropic's advisor tool (executor + advisor pattern), rebuilt for local Claude Code orchestration where the advisor is a subagent and sees only what you send it — which is exactly where the token savings live.

A disciplined consult costs roughly $0.15–0.50. A wrong architecture costs hours of rework, thousands of Opus tokens, and your time.

What's inside

Install

In any Claude Code session:

/plugin marketplace add czlonkowski/fable-advisor
/plugin install fable-advisor@fable-advisor

Or interactively: run /plugin marketplace add czlonkowski/fable-advisor once, then open /plugin → Browse plugins and install fable-advisor from there.

Recommended: add this line to your project or global CLAUDE.md — it makes the skill fire deterministically instead of relying on Claude's own skill-triggering judgment (see Making it fire reliably for why):

Before committing to any costly-to-revert decision (architecture, DB schema, API/webhook
contracts, technology selection, production migration plans), or when stuck after 2+
failed fix attempts, consult the fable-advisor skill first.

Requirements: Claude Code with Fable 5 available as a subagent model. Designed for sessions where the base model is Opus (works from any orchestrator model below Fable).

Making it fire reliably

We benchmarked the skill's triggering on 20 realistic queries (10 should-fire, 10 tricky near-miss negatives) across four description variants, ~200 runs on Opus. Result: zero false-fires in every variant — the skill never triggered on trivial changes, decided architectures, or questions about Fable — but recall on bare decision prompts plateaued around 50–60% regardless of description wording. The cause is structural: Claude Code consults skills only for tasks it can't handle alone, and Opus believes (correctly, in a narrow sense) that it can answer a design question itself. That belief is the exact failure mode this skill exists to counter.

If you want deterministic triggering, add one line to your project or global CLAUDE.md:

Before committing to any costly-to-revert decision (architecture, DB schema, API/webhook
contracts, technology selection, production migration plans), or when stuck after 2+
failed fix attempts, consult the fable-advisor skill first.

Naming it also works: prompts that mention Fable, a "second opinion", or "check with a stronger model" trigger far more reliably (see Prompts to try below).

How it works

The gate — two questions before every consult:

1. Is this decision costly to revert, or am I genuinely stuck?
2. Is there a real fork in the road, with evidence to weigh?

If either is "no", the orchestrator decides on its own.

The four triggers:

1. Costly-to-revert decision, before building — architecture, DB schema, API/webhook contracts, n8n workflow topology, technology selection
2. Stuck escalation — 2+ genuinely different failed attempts, evidence in hand
3. Plan review — a draft implementation plan embedding a costly-to-revert choice
4. Pre-completion review — before declaring done on production deploys, migrations, client-facing deliverables

The budget (hard rules):

• Default one consult per task, hard cap three Fable interactions
• Every consult announced to the user in one line before it happens
• One spawn + at most one reconcile follow-up per question
• Generation work (code, docs, configs, workflows) never goes to Fable

The briefing packet: decision in the first line, options with a stated leaning, hard constraints, curated evidence, ≤5 file pointers the advisor may read narrowly — and an explicit answer-format request, because advisor output is the biggest cost driver (Anthropic measured ~7× output reduction from capping, with no quality loss).

What a consult looks like

Consulting Fable on sync architecture (trigger: costly-to-revert, consult 1/3).

→ Fable verdict: nightly batch delta sync; per-document webhooks add SharePoint
  subscription-renewal failure modes your one-person team can't absorb. Revisit if
  freshness requirements drop below 4 hours.

Prompts to try

In the style of the Claude Code prompt library:

plan how to migrate our API from REST to gRPC — this is hard to undo once services depend on it, so get a Fable verdict on the approach before finalizing

I'm torn between Postgres LISTEN/NOTIFY and a proper queue for job dispatch. decide, and check the decision with Fable before we build around it

review my deploy plan for Saturday's production migration and fix anything risky before I run it

The skill can also trigger without Fable being named when a task hits a costly-to-revert decision, a stuck debugging loop, or a pre-production review — but unnamed triggering is ~50–60% reliable in our benchmark. For deterministic behavior, use the one-line CLAUDE.md setup from the Install section.

Evals

The repo ships the eval scenarios used to develop the skill (evals/): an architecture-decision task (should consult once), a trivial-change task (should not consult at all), and a production-migration plan review (should consult before finalizing). Runs compare with-skill vs. no-skill orchestrators on consult discipline, briefing compactness, and outcome quality.

Measured results (v0.1, 3 scenarios × with/without skill, Opus orchestrators):

• Consult discipline was perfect: exactly 1 consult on each costly-to-revert task, 0 on the trivial task. Briefings came in at ~511 words — well under budget — and every consult was announced to the user with the verdict relayed afterward.
• On the trivial task the skill added zero overhead (same duration as baseline, ~half the output tokens).
• The consults earned their keep: in the architecture task Fable corrected the polling cadence and contributed the failure-mode list; in the migration review it confirmed the orchestrator's 8 fixes and added 3 gaps the orchestrator had missed (window pre-staging, owner-account ordering before credential import, webhook re-registration verification).
• Trigger benchmark: ~200 runs across 4 description variants — zero false-fires, which is why the budget rules can afford to be generous about consulting.

Author

Built by Romuald Członkowski @aiadvisors.

License

MIT — © 2026 Romuald Członkowski @aiadvisors