---
name: silent-failures-are-evil
description: No silent failures — use when writing or reviewing error handling: catch blocks, promise rejections, fallbacks for unsupported features, or any branch that treats a result as "didn't work"; when a UI shows a failure with nothing logged; when someone says "silent failure". Every failure path leaves a trace in the logs, and no failure is invented without checking what the API actually returns.
---

# Silent failures are evil

A failure nobody can see is a failure nobody can fix. Every failure path
must leave a trace.

## the rules

- **Log every failure path**: a caught exception, a rejected promise, a
  falsy result treated as "didn't work", an unsupported-feature
  fallback. Changing a label on screen is not enough — log it, with an
  `event` tag for grepping, and no secrets (no keys, cookies, header or
  param values).
- **Don't invent failures.** Before branching on a result, check what
  the API actually returns (the spec or MDN, not a guess). A success
  misreported as failure is as bad as a failure reported as nothing.
- **Say only what you know.** When an API can't tell you the outcome,
  report what it did tell you ("offered", not "saved").
- **Make it testable.** Pass the logger in (see
  [ocap-discipline](../ocap-discipline/SKILL.md)) so a test can assert
  that the failure path logged; a discovered silent failure is a goof
  that owes a test ([lazy-tdd](../lazy-tdd/SKILL.md)).

## the goof that prompted this

diigo-cache's password-manager save button said "not saved", with
nothing in the console. The code read `c ? "saved" : "not saved"` on the
result of [`CredentialsContainer.store()`](https://developer.mozilla.org/en-US/docs/Web/API/CredentialsContainer/store),
which resolves with `undefined` per spec — even on success. So every
save was reported as a failure, silently. The fix
(`capsite/diigo-cache/src/pm-save.ts`) reports "offered", logs every
outcome, and is covered by `tests/pm-save.test.ts`.