Agent Error Handling: Full Benchmark Results
Notebook #20 — LangChain 1.2 vs SynapseKit 1.4 vs LlamaIndex Core 0.14 · built-in primitives only, no custom resilience libraries
Feature Depth Score — Built-In Error Handling (out of 7)
LangChain
6
out of 7 features
SynapseKit
3
out of 7 features
LlamaIndex
1
out of 7 features
LoC to Add Error Handling & Feature Depth
Feature Matrix — Built-In Error Handling Primitives
| Feature |
LangChain |
SynapseKit |
LlamaIndex |
| Dedicated exception type | Yes | No | No |
| Error → LLM observation (built-in) | Yes | No | No |
| Handle LLM parse errors | Yes | No | No |
| LLM fallback chain | Yes | Yes | No |
| Circuit breaker | No | Yes | No |
| Max iterations guard | Yes | Yes | Yes |
| Custom error handler fn | Yes | No | No |
| Score (out of 7) | 6 | 3 | 1 |
Key Finding: The Complementary Gap
LangChain handles tool errors. SynapseKit handles model errors. Neither covers both.
LangChain's ToolException converts tool failures into LLM observations — the model reasons through them. SynapseKit's FallbackChain and CircuitBreaker handle LLM-level failures — rate limits, model unavailability, repeated service outages. These are different failure classes. A production agent that handles both needs primitives from both frameworks, or custom code to fill the gap in whichever framework you chose. LlamaIndex assumes you bring all of this yourself.
Design Philosophy
LangChain
Error as observation
ToolException + handle_tool_error routes failures to the LLM reasoning loop. handle_parsing_errors retries malformed outputs. 6/7 built-in features. The LLM is the error handler — powerful for recoverable errors, a loop risk for hard failures without max_iterations.
SynapseKit
LLM-level resilience
Manual try/except for tool errors. FallbackChain for model unavailability. CircuitState stops hammering broken services. 3/7 built-in features — but covers the production failure modes LangChain misses: rate limits and repeated outages.
LlamaIndex
Bring your own
max_iterations is the only guard. All other error handling is manual — wrapper functions, return error strings, attach your own Tenacity/Polly/custom retry logic. 1/7 built-in. Maximum composability. Minimum convention.
Summary Table
| Criterion |
LangChain |
SynapseKit |
LlamaIndex |
| Fewest error-handling lines | 🏆 5 | 7 | 8 |
| Built-in feature depth | 🏆 6/7 | 3/7 | 1/7 |
| Circuit breaker (built-in) | ❌ No | 🏆 Yes | ❌ No |
| LLM model fallback | ✅ Yes (.with_fallbacks) | ✅ Yes (FallbackChain) | ❌ No |
| Parse error handling | 🏆 Yes | No | No |
| Composability with own libs | Partial | Good | 🏆 Best |