diff --git a/tickets/051-delete-metrics.md b/tickets/051-delete-metrics.md
new file mode 100644
index 0000000..47e38f2
--- /dev/null
+++ b/tickets/051-delete-metrics.md
@@ -0,0 +1,64 @@
+# 051 — Allow deleting a declared metric
+
+## Summary
+
+There is currently no way to delete a metric once declared. `src/api.rs`
+only routes `GET`/`POST /api/metrics` and `GET`/`PUT /api/metrics/{name}`
+(`src/api.rs:132-135`) — there is no `DELETE`. The engine already has the
+machinery for it internally: `EngineMessage::RemoveMetricDeclaration`
+(`src/engine.rs:103`) removes a metric's declaration from the index, but
+it is only ever sent as part of `delete_profile`'s cleanup
+(`src/api.rs:689`) when an entire profile is deleted, not as a
+user-facing action on a single metric. Persistence has the same gap:
+`Settings`/profile storage (`src/profile.rs`, post ticket 049 now inline
+in `settings.json`) has `record_metric_declaration`/
+`record_metric_declaration_update` but no corresponding removal method, so
+even if a metric were removed from the live engine index there'd be
+nothing to stop it reappearing on next load. The webapp UI
+(`webapp/src/components/Metrics.tsx`) has no delete affordance either —
+compare to param declarations, which have the same underlying gap (no
+`RemoveParamDeclaration`-triggering UI or persisted-removal path either),
+though this ticket is scoped to metrics only.
+
+## Scope
+
+- Add `DELETE /api/metrics/{name}` in `src/api.rs`, sending
+  `EngineMessage::RemoveMetricDeclaration` to the engine (same message
+  the profile-delete cleanup path already uses) and returning 404 if the
+  metric doesn't exist.
+- Add a persisted-removal method (e.g. `Settings::remove_metric_declaration`
+  or equivalent, alongside `record_metric_declaration`/
+  `record_metric_declaration_update` in `src/profile.rs`/`src/settings.rs`)
+  so a deleted metric doesn't reappear when declarations replay from
+  `settings.json` on the next restart, and call it from the new route the
+  same way `persist_metric_declaration` is called from `declare_metric`.
+- Add a delete affordance in `webapp/src/components/Metrics.tsx` (icon
+  button or similar, following whatever confirm-before-destructive-action
+  pattern already exists elsewhere in the settings/profile UI — check
+  `NavMenu.tsx`'s profile deletion for the existing convention) that calls
+  the new endpoint and removes the metric from the list on success.
+- Decide and document what happens to bucket-value history already
+  recorded under the deleted metric's name (e.g. `MetricPrimitive` samples
+  indexed by metric name in the engine) — either leave it orphaned
+  (queryable by name won't work without a declaration, but doesn't need
+  active cleanup) or purge it; state the choice in the PR.
+- Decide and document what happens to dashboard panels or alert rules
+  whose PromQL query text/filter references the deleted metric by name —
+  at minimum they should fail gracefully (a clear "unknown metric" error
+  rather than a panic or silent empty result) rather than needing to be
+  actively kept in sync; a full dependent-reference check/warning before
+  delete is out of scope unless trivial.
+
+## Acceptance criteria
+
+- A metric can be deleted via the API and the UI; it disappears from
+  `GET /api/metrics` immediately and does not reappear after a restart.
+- Deleting an unknown metric name returns a clear 404, not a 500 or panic.
+- A dashboard panel or alert rule referencing the deleted metric by name
+  fails with a readable error rather than crashing the engine or API,
+  verified with a seeded fixture.
+
+## Depends on
+
+None (touches the same engine/persistence seam as ticket 049, but that
+ticket is already merged).