Error classification engine. Rules for the obvious, LLM for the ambiguous.
Most errors are easy to classify — a 400 is a client error, a 502 is a server error. But some aren't — a 500 with "model not found" in the body is actually a client error, not a server failure. Your rules can't catch every edge case. An LLM can.
ErrorSense runs errors through a phase pipeline: fast deterministic rulesets first, LLM only when rulesets can't decide. Most errors never hit the LLM. The ones that do get classified correctly instead of falling through as "unknown."
Use it for: circuit breakers, alert routing, retry logic, error dashboards; anywhere you need to know what kind of error happened, not just that it happened.
pip install errorsense # core only (zero dependencies)
pip install errorsense[llm] # + LLM classificationfrom errorsense.presets import http
from errorsense import LLMConfig, Signal
sense = http(llm=LLMConfig(api_key="your_api_key"))
results = sense.classify(Signal.from_http(status_code=400, body="bad request"))
results[0].label # "client"
results = sense.classify(Signal.from_http(status_code=502))
results[0].label # "server"
results = sense.classify(Signal.from_http(status_code=500, body="model not found"))
results[0].label # "client" (LLM figured it out)The http preset gives you a 3-phase pipeline (rules → patterns → LLM) with 3 labels: "client", "server", "undecided". Rulesets handle obvious cases instantly. LLM handles the ambiguous ones.
Don't want LLM? Use http_no_llm() — rulesets only, ambiguous errors come back as "undecided".
A pipeline is a list of phases. Each phase has rulesets (deterministic) or skills (LLM). You can mix both, use only rulesets, or use only skills.
from errorsense import ErrorSense, Phase, Ruleset, Skill, LLMConfig, Signal
# Rulesets + LLM
sense = ErrorSense(
labels=["transient", "permanent", "user"],
pipeline=[
Phase("codes", rulesets=[
Ruleset(field="error_code", match={
"ECONNRESET": "transient", "ETIMEOUT": "transient", "EPERM": "permanent",
}),
]),
Phase("patterns", rulesets=[
Ruleset(field="message", patterns=[
("transient", [r"timeout", r"connection reset", r"retry"]),
("permanent", [r"corruption", r"fatal"]),
]),
]),
Phase("llm", skills=[
Skill("my_classifier", path="./skills/my_classifier.md"),
], llm=LLMConfig(api_key="your_key")),
],
default="transient",
)
# Rulesets only — no LLM needed
sense = ErrorSense(
labels=["client", "server"],
pipeline=[
Phase("rules", rulesets=[
Ruleset(field="status_code", match={"4xx": "client", 502: "server"}),
]),
],
default="server",
)
# LLM only — skip rulesets entirely
sense = ErrorSense(
labels=["client", "server"],
pipeline=[
Phase("llm", skills=[
Skill("my_classifier", path="./skills/my_classifier.md"),
], llm=LLMConfig(api_key="your_key")),
],
default="unknown",
)Phases run in order. First match wins. Rulesets are instant and free. LLM is the fallback.
Each ruleset does one thing — match= for exact field matching or patterns= for regex:
Ruleset(field="status_code", match={400: "client", 502: "server"}) # exact match
Ruleset(field="status_code", match={"4xx": "client", 503: "server"}) # range match
Ruleset(field="body.error.type", match={"validation_error": "client"}) # JSON dot-path
Ruleset(field="headers.content-type", patterns=[("server", [r"^text/html"])]) # regex
Ruleset(field="body", patterns=[("server", [r"OOM"]), ("client", [r"invalid"])]) # regexCustom logic? Subclass:
class VendorBugRuleset(Ruleset):
def classify(self, signal: Signal) -> SenseResult | None:
if signal.get("vendor") == "acme" and signal.get("code") == "X99":
return SenseResult(label="known_bug", confidence=1.0)
return NoneSkills are LLM instructions stored as .md files. Each skill teaches the LLM how to classify errors in a specific domain. Each skill triggers a separate LLM call — highest confidence result wins.
# Loads from errorsense/skills/http_classifier.md (built-in)
Skill("http_classifier")
# Loads from your own file
Skill("my_classifier", path="./skills/my_classifier.md")Multiple skills in one phase: Use this when you want multiple domain-specific opinions on the same error.
Phase("llm", skills=[
Skill("http_classifier"), # knows HTTP error patterns
Skill("db_classifier"), # knows database error patterns
], llm=LLMConfig(...))In sync (classify), skills run sequentially. In async (async_classify), skills run concurrently.
# Default — stops at first match
results = sense.classify(signal)
# All phases run
results = sense.classify(signal, short_circuit=False)
# With LLM reasoning
results = sense.classify(signal, explain=True)
results[0].reason # "ECONNRESET indicates transient network failure"Track errors per key. When a threshold is hit, optionally have an LLM review the full error history.
from errorsense import LLMConfig, TrailingConfig
# With LLM review at threshold
sense = ErrorSense(
labels=["transient", "permanent", "user"],
pipeline=[...],
trailing=TrailingConfig(
threshold=3,
count_labels=["transient", "permanent"], # user errors don't count
reviewer_llm=LLMConfig(), # enables LLM review
),
)
# Without LLM review (just counting)
trailing=TrailingConfig(threshold=3, count_labels=["transient", "permanent"])
# In your error handler:
result = sense.trail("service-a", signal)
result.label # "transient"
result.at_threshold # True (3rd counted error)
result.reason # LLM review: "3 transient errors — all connection resets..."
# On success:
sense.reset("service-a")How it works:
- Each
trail()call classifies the signal normally through the pipeline - Counted labels accumulate per key toward the threshold
- At threshold, the LLM reviews all recorded errors (if
reviewer_llmis set) - If the review changes the label, the history entry is corrected and the count adjusts
reviewer_skill=Skill(...)lets you override the default review instructions
Manual review anytime:
verdict = sense.review("service-a")
verdict.label # LLM's verdict on the full history
verdict.reason # explanationMIT