grouping-noisy-errors

Search by exception type or message to find candidates:

posthog:query-error-tracking-issues-list
{
  "searchQuery": "TypeError: Cannot read property",
  "status": "active",
  "limit": 50,
  "orderBy": "occurrences",
  "dateRange": { "date_from": "-30d" }
}

For each candidate, pull one sampled exception event to compare stack, type, and message:

posthog:query-error-tracking-issue-events
{
  "issueId": "<candidate_issue_id>",
  "limit": 1,
  "include": ["exception", "stacktrace", "environment"]
}

Run this once per candidate. The tool defaults to onlyAppFrames: true, which makes the top in-app frame stand out at a glance. If two candidates share the same top frame and same exception type, they're likely the same error — but verify against the full checklist below before merging.

Treat two issues as duplicates only when every one of these matches:

• $lib is the same SDK. The browser/JS SDK captures $lib as web (not posthog-js); server SDKs use posthog-python, posthog-node, etc. Confirm the exact value with read-data-schema (event_property_values for $lib on $exception) rather than assuming — a wrong value silently matches nothing. Errors from different SDKs almost always come from different code paths even when the exception type matches.
• The exception type is identical ($exception_types).
• The top in-app stack frame points at the same file and same function. Line numbers and minor offsets within that function are fine; a different file or a different function on top means a different bug.
• The message follows the same template, with differences confined to volatile data — IDs, hashes, timestamps, dynamic paths. If the difference is a different verb, object, or operation, it's a different bug.
• $exception_handled agrees (both handled or both unhandled). A caught variant and an uncaught variant are different code paths and benefit from staying separate.

If any single one of those differs, they are not duplicates — investigate separately (investigating-error-issue).

These are the failure modes that destroy debugging signal. Do not group across any of them, even when the user describes them as "the same kind of bug":

• Frontend and backend variants of the same exception type. A TypeError from a browser bundle and a TypeError from a Node service share a name and often a message word, but the stack, the runtime, and the fix all differ.
• Different SDKs / platforms. web (browser/JS) vs posthog-python vs posthog-node are different call sites.
• Same type, different file or function on top of the stack. A NullPointerException thrown from OrderService.cancel is not the same bug as one thrown from PaymentService.refund, even if both messages say "user was null".
• Caught vs uncaught. Two issues that differ only in $exception_handled are usually a code path that swallows the error in one place and lets it propagate in another — keeping them separate makes that visible.
• Conceptually-similar bugs that happen to share a phrase. "Cannot read property of undefined" appears in many independent bugs. Without matching stack frames, message similarity alone is not enough.

Pick the issue that should absorb the others:

• Most occurrences — keeps the dominant issue so dashboards stay continuous
• Best name and description — if the user has annotated one, prefer it
• Earliest first_seen — preserves the original timeline

Note the target's ID. The other candidates become ids to merge in.

posthog:error-tracking-issues-merge-create
{
  "id": "<target_issue_id>",
  "ids": ["<duplicate_id_1>", "<duplicate_id_2>", "..."]
}

Merge is destructive (annotation destructive: true) — once issues are merged into a target, the source issues are gone from the active list. Confirm the target with the user before calling. Cap each merge call at ~50 source IDs to keep failures localized; for larger sprawl, batch.

Merged changes may not appear in the issue list immediately — re-listing right after the call can still show the source issues for a short window. If a follow-up error-tracking-issues-list call looks unchanged, wait a few seconds and re-query rather than re-issuing the merge.

If after the merge the target's metadata looks wrong (a duplicate had a better name), use error-tracking-issues-partial-update to fix the name or description on the target rather than re-merging.

A grouping rule is worth creating when both are true:

• The pattern keeps producing new fingerprints (you have seen new duplicates appear since the last merge)
• You can describe the pattern with property filters that won't accidentally swallow unrelated errors

The canonical exception properties ($exception_types, $exception_values for messages, $exception_sources for file paths, $exception_functions for function names) are arrays at capture time. PostHog's property filters special-case them — each filter matches against the individual array elements, so all the standard operators (exact, is_not, icontains, not_icontains, regex, not_regex) work with the bare value: exact "TypeError", not exact '["TypeError"]' or regex '"TypeError"'.

The singular forms ($exception_type, $exception_message) and $exception_stack_trace_raw are emitted on a fraction of a percent of events; filtering on them produces a rule that silently never matches.

If the volatility is in the message (e.g., TypeError at /static/main.<hash>.js), a regex filter on $exception_values works. If the volatility is in line numbers within a known file, icontains on $exception_sources does. $exception_handled is also a useful narrowing dimension — separate handled vs unhandled rather than mixing them.

Skip the grouping rule when:

• The duplicates are historical (one-off backfill, no new occurrences) — merge is enough
• You can't write a filter narrow enough to be safe — broaden the merge cadence instead and revisit later

Translate the step 1 "same error" checklist into rule filters. A rule that matches more loosely than the checklist will silently merge unrelated bugs forever — the rule is more dangerous than the merge because it runs against every future event. At a minimum, scope by SDK and exception type, and add a third dimension (file path via $exception_sources, or a specific message phrase via $exception_values) to pin the call site.

Confirm the $lib value first — the browser/JS SDK captures $lib="web", not posthog-js, so a rule filtering on posthog-js silently never matches. Verify with read-data-schema (event_property_values for $lib on $exception) before baking a value into the rule:

posthog:error-tracking-grouping-rules-create
{
  "filters": {
    "type": "AND",
    "values": [
      {
        "type": "event",
        "key": "$lib",
        "operator": "exact",
        "value": "web"
      },
      {
        "type": "event",
        "key": "$exception_types",
        "operator": "exact",
        "value": "TypeError"
      },
      {
        "type": "event",
        "key": "$exception_sources",
        "operator": "icontains",
        "value": "/static/checkout/"
      },
      {
        "type": "event",
        "key": "$exception_values",
        "operator": "icontains",
        "value": "Cannot read property"
      }
    ]
  },
  "description": "Cleanup: collapse noisy checkout TypeError fingerprints (web)"
}

Rules are evaluated in order. List existing rules first (posthog:error-tracking-grouping-rules-list) — if a rule already partially covers the pattern, prefer adjusting its filter over stacking a near-duplicate.

The optional assignee field auto-assigns issues created by the rule. Skip it unless the user explicitly wants ownership baked into the rule.

Sample the merged issue's recent events to confirm the merge succeeded. Watch for the rule's custom-rule:<rule_id> fingerprint to start matching events — the first match creates a new issue (or routes to whatever was already bound to that fingerprint). To keep events under your historical target rather than scattered across the new custom-rule issue, run a second merge folding the custom-rule issue into the target.

If new (non-rule) fingerprints continue appearing despite the rule, its filter is too narrow — widen it.