sickn33/agentic-awesome-skills · error · Error

Invalid JSON: ${error}

Error message

Invalid JSON: ${error}

What it means

In the fp-refactor skill's before-code, parseJSON catches JSON.parse's SyntaxError and re-wraps it with the 'Invalid JSON' prefix. It fires whenever the input string is not well-formed JSON — the skill uses it to motivate error-as-value refactoring.

Source

Thrown at skills/fp-refactor/SKILL.md:62

### The Problem with try-catch

Traditional try-catch blocks have several issues:
- Error handling is implicit and easy to forget
- The type system doesn't track which functions can throw
- Control flow is non-linear and harder to reason about
- Composing multiple fallible operations is verbose

### Pattern: Synchronous try-catch to Either

#### Before (Imperative)

```typescript
function parseJSON(input: string): unknown {
  try {
    return JSON.parse(input);
  } catch (error) {
    throw new Error(`Invalid JSON: ${error}`);
  }
}

function validateUser(data: unknown): User {
  try {
    if (!data || typeof data !== 'object') {
      throw new Error('Data must be an object');
    }
    const obj = data as Record<string, unknown>;
    if (typeof obj.name !== 'string') {
      throw new Error('Name is required');
    }
    if (typeof obj.age !== 'number') {
      throw new Error('Age must be a number');
    }
    return { name: obj.name, age: obj.age };
  } catch (error) {
    throw error;

View on GitHub (pinned to 58d857988f)

Solutions

1. Log the offending substring around the parse position to find the malformed token
2. If APIs may return HTML error pages, check content-type before parsing
3. Return E.Either<Error, unknown> from parseJSON instead of throwing (the skill's refactor direction)

Example fix

// before
try { return JSON.parse(input) } catch (e) { throw new Error(`Invalid JSON: ${e}`) }

// after
const parseJSON = (input: string): E.Either<Error, unknown> =>
  E.tryCatch(() => JSON.parse(input), E.toError)

const looksLikeJson = (s: string) => /^\s*[\[\{"\d-tnf]/.test(s)

try {
  JSON.parse(input)
} catch (e) {
  // e is SyntaxError with position info; log input around e.message
}

When it happens

Trigger: Calling parseJSON with truncated payloads, single quotes, trailing commas, unquoted keys, plain text/HTML error pages from an API, or an empty string.

Common situations: APIs returning HTML error pages with 200 status; truncated responses from cut connections; log lines with JSON-ish prefixes; hand-built strings missing quotes.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Invalid range "${t}" in ${fieldDef.name}
• Expected 5 fields (got ${parts.length}). Format: minute hour
• Invalid age
• Age cannot be negative
• Value ${v} out of range for ${fieldDef.name} (${fieldDef.min

AI-assisted analysis of sickn33/agentic-awesome-skills@58d857988f (2026-08-26). Data as JSON: /api/errors/398c6914018a850d. Report an issue: GitHub.