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Developer creates 300-case suite to test LLM JSON parsing robustness

A developer has created a 300-case conformance suite, named MALFORMED-300, to test the robustness of Large Language Model (LLM) parsers when handling malformed JSON output. The suite categorizes errors into twelve types, including code fences, prose wrappers, and Python/JS literals, with a specific focus on cases where the only correct response is to refuse parsing. Initial tests revealed that the standard Python `json` library fails on 275 out of 300 cases, while the developer's own parser achieved a 94.0% success rate but still made five critical errors, including silently laundering redacted data into a customer relationship management system. AI

IMPACT Highlights critical parsing vulnerabilities in LLM agents, potentially leading to more robust data handling and fewer silent failures in downstream systems.

RANK_REASON Developer-created tool for testing LLM output parsing.

Read on dev.to — LLM tag →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

Developer creates 300-case suite to test LLM JSON parsing robustness

COVERAGE [1]

  1. dev.to — LLM tag TIER_1 English(EN) · Toolkit Labs ·

    I built a 300-case conformance suite for LLM JSON parsing, and it found 18 failures in my own parser

    <p>Every team shipping an LLM agent writes the same 40 lines eventually: strip the code fence, find the outermost braces, try <code>json.loads</code>, fall back to a regex, give up and return <code>{}</code>.</p> <p>That last step is the one that hurts. Returning <code>{}</code> …