etiology

A bug-fixing guide says to trace a defect's cause before changing code. Etiology means the chain of events that produced the visible problem.

In plain words
What is it for?
It guides developers through identifying the user-visible fault, nearby incorrect code, API expectations, and whether the problem is local or systemic.
Why use it?
It helps prevent patches that hide symptoms while leaving the underlying bug in place.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/gridaco/grida/etiology
Any agent
npx skills add gridaco/grida --skill etiology
Clone the repo
git clone --depth 1 https://github.com/gridaco/grida

Made for: Claude Code, Codex.

Per session 101 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,122 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00101 $0.01122
Opus 5 $0.00051 $0.00561
Sonnet 5 $0.00020 $0.00224
Haiku 4.5 $0.00010 $0.00112

Measured 3d ago against content hash 687cbe01fa3f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

etiology scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

  • etiology — 100% identical, 0 lines differ
.agents/skills/etiology/SKILL.md · 113 lines

How it starts

The opening of the file, as written. The whole thing — 113 lines — stays where its author put it; the contents beside it link to each section on GitHub.

etiology

The temptation in a bug fix is to suppress the symptom. The discipline is to know which fix you wrote: the one that addressed the cause, or the one that masked it. Every bug has an etiology — the chain of cause that produced the observable fault — and a fix is only honest once that chain has been traced.

Errors only grow. A bandaid leaks into adjacent call sites, and the next reader inherits both the original defect and the workaround that obscures it. Be fixated on the etiology; the symptom is what alerted you to the bug, not the bug itself. A bandaid is occasionally correct, but it is never the default.

The diagnostic ladder

Before writing the fix, walk the ladder. Each rung is a question the next rung depends on; skipping a rung produces a fix that doesn't know what it is.

  1. Presentation. What is the user-observable fault? State the symptom precisely — not the suspected cause, the symptom.
  2. Proximate cause. Which specific code is wrong, and is the defect at the line you would patch, or upstream of it? The line that fires the error is rarely the line that contains it.
  3. API contract. Was the abstraction we relied on misleading — i.e., would another developer following normal patterns re-trigger the same bug at a different call site? If yes, the defect is in the interface, not the caller.
  4. Isolated or systemic. Is this a self-contained oversight, or one presentation of a broader pathology in the surrounding code? If broader, scope the fix to the broader cause; patching one of N produces N − 1 future bug reports.

Stating in the PR description which rung you stopped at — and why — keeps the review honest.

Coverage cuts both ways

  • Should-have-been covered. The defect slipped a test that ought to exist. The fix carries that test — coverage earned by a regression is the cheapest coverage you will ever buy.
  • Impossible to cover. Interactive timing, render-order asymmetries, benchmark-only drift, layered composition where the execution order is the behavior — defects of this kind have no defense once shipped. That raises the bar on the fix, not lowers it. Prefer the underlying refactor; if you must ship a surgical patch, document the constraint at the call site so the next reader sees both the symptom and the rule that keeps it from recurring.

Read the full file on GitHub · 113 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 113 lines · 101 tokens per session scan A 687cbe01fa3f

Subscribe to this mod's changes

etiology is a skill published in the GitHub repository gridaco/grida (2,629 stars, last pushed 12d ago), licensed Apache-2.0. It adds 101 tokens to every session and 1,122 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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