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+# DIDWW 2026-04-16 — Server-side filter reference
+
+This is the canonical list of `filter[KEY]` query parameters accepted by each list endpoint of the DIDWW API at version `2026-04-16` — the default API version targeted by this SDK.
+
+The SDK passes filters through as untyped string→string maps (e.g. `QueryParams().filter("country.id", uuid)`), so this document is the authoritative source for which keys actually do something on the server.
+
+Every key listed here was verified live against the DIDWW API at version `2026-04-16`.
+
+Pass values URL-encoded as strings. Where the server accepts arrays, comma-separate the values.
+
+## AddressRequirement — `GET /v3/address_requirements`
+
+- `filter[country.id]`
+- `filter[did_group_type.id]`
+
+## Address — `GET /v3/addresses`
+
+- `filter[address]`
+- `filter[address_contains]`
+- `filter[area.id]`
+- `filter[city.id]`
+- `filter[city_name]`
+- `filter[city_name_contains]`
+- `filter[country.id]`
+- `filter[description]`
+- `filter[description_contains]`
+- `filter[external_reference_id]`
+- `filter[identity.external_reference_id]`
+- `filter[identity.id]`
+- `filter[postal_code]`
+- `filter[postal_code_contains]`
+
+## AddressVerification — `GET /v3/address_verifications`
+
+- `filter[address.id]`
+- `filter[address.identity.id]`
+- `filter[external_reference_id]`
+- `filter[reference]`
+- `filter[reference_in]`
+- `filter[status]`
+
+## Area — `GET /v3/areas`
+
+- `filter[country.id]`
+- `filter[name]`
+
+## AvailableDid — `GET /v3/available_dids`
+
+- `filter[city.id]`
+- `filter[country.id]`
+- `filter[did_group.features]`
+- `filter[did_group.id]`
+- `filter[did_group.needs_registration]`
+- `filter[did_group_type.id]`
+- `filter[nanpa_prefix.id]`
+- `filter[number_contains]`
+- `filter[region.id]`
+
+## CapacityPool — `GET /v3/capacity_pools`
+
+- `filter[country.id]`
+- `filter[has_unassigned_channels]`
+- `filter[name]`
+
+## City — `GET /v3/cities`
+
+- `filter[area.id]`
+- `filter[country.id]`
+- `filter[is_available]`
+- `filter[name]`
+- `filter[region.id]`
+
+## Country — `GET /v3/countries`
+
+- `filter[is_available]`
+- `filter[iso]`
+- `filter[name]`
+- `filter[prefix]`
+
+## DidGroup — `GET /v3/did_groups`
+
+- `filter[allow_additional_channels]`
+- `filter[area_name]`
+- `filter[available_dids_enabled]`
+- `filter[city.id]`
+- `filter[country.id]`
+- `filter[did_group_type.id]`
+- `filter[features]`
+- `filter[is_available]`
+- `filter[is_metered]`
+- `filter[meta.total_count_gteq]`
+- `filter[nanpa_prefix.id]`
+- `filter[nanpa_prefix.npanxx]`
+- `filter[needs_registration]`
+- `filter[prefix]`
+- `filter[region.id]`
+
+## DidGroupType — `GET /v3/did_group_types`
+
+- `filter[name]`
+
+## DidHistory — `GET /v3/did_history`
+
+- `filter[action]`
+- `filter[created_at_gteq]`
+- `filter[created_at_lteq]`
+- `filter[did_number]`
+- `filter[method]`
+
+## DidReservation — `GET /v3/did_reservations`
+
+- `filter[description]`
+
+## Did — `GET /v3/dids`
+
+- `filter[address_verification.id]`
+- `filter[awaiting_registration]`
+- `filter[billing_cycles_count]`
+- `filter[blocked]`
+- `filter[capacity_pool.id]`
+- `filter[city.id]`
+- `filter[country.id]`
+- `filter[description]`
+- `filter[did_group.features]`
+- `filter[did_group.id]`
+- `filter[emergency_calling_service.id]`
+- `filter[emergency_enabled]`
+- `filter[number]`
+- `filter[order.id]`
+- `filter[order.reference]`
+- `filter[region.id]`
+- `filter[shared_capacity_group.id]`
+- `filter[terminated]`
+- `filter[voice_in_trunk.id]`
+- `filter[voice_in_trunk_group.id]`
+
+
+## EmergencyCallingService — `GET /v3/emergency_calling_services`
+
+- `filter[address.id]`
+- `filter[country.id]`
+- `filter[did_group_type.id]`
+- `filter[identity.id]`
+- `filter[name]`
+- `filter[reference]`
+- `filter[status]`
+
+## EmergencyRequirement — `GET /v3/emergency_requirements`
+
+- `filter[country.id]`
+- `filter[did_group_type.id]`
+
+## EmergencyVerification — `GET /v3/emergency_verifications`
+
+- `filter[emergency_calling_service.id]`
+- `filter[external_reference_id]`
+- `filter[status]`
+
+## Export — `GET /v3/exports`
+
+- `filter[external_reference_id]`
+
+## Identity — `GET /v3/identities`
+
+- `filter[birth_date]`
+- `filter[company_name]`
+- `filter[company_name_contains]`
+- `filter[company_reg_number]`
+- `filter[company_reg_number_contains]`
+- `filter[country.id]`
+- `filter[description]`
+- `filter[description_contains]`
+- `filter[external_reference_id]`
+- `filter[first_name]`
+- `filter[first_name_contains]`
+- `filter[id_number]`
+- `filter[id_number_contains]`
+- `filter[identity_type]`
+- `filter[last_name]`
+- `filter[last_name_contains]`
+- `filter[personal_tax_id]`
+- `filter[personal_tax_id_contains]`
+- `filter[phone_number]`
+- `filter[phone_number_contains]`
+- `filter[vat_id]`
+- `filter[vat_id_contains]`
+
+## NanpaPrefix — `GET /v3/nanpa_prefixes`
+
+- `filter[country.id]`
+- `filter[did_group.features]`
+- `filter[did_group.is_available]`
+- `filter[npa]`
+- `filter[npanxx]`
+- `filter[nxx]`
+- `filter[region.id]`
+
+## Order — `GET /v3/orders`
+
+- `filter[created_at_gteq]`
+- `filter[created_at_lteq]`
+- `filter[external_reference_id]`
+- `filter[reference]`
+- `filter[status]`
+
+## PermanentSupportingDocument — `GET /v3/permanent_supporting_documents`
+
+- `filter[external_reference_id]`
+
+## Proof — `GET /v3/proofs`
+
+- `filter[external_reference_id]`
+
+## ProofType — `GET /v3/proof_types`
+
+- `filter[entity_type]`
+
+## Region — `GET /v3/regions`
+
+- `filter[country.id]`
+- `filter[iso]`
+- `filter[name]`
+
+## SharedCapacityGroup — `GET /v3/shared_capacity_groups`
+
+- `filter[capacity_pool.id]`
+- `filter[external_reference_id]`
+- `filter[name]`
+
+## SupportingDocumentTemplate — `GET /v3/supporting_document_templates`
+
+- `filter[name]`
+- `filter[name_contains]`
+- `filter[permanent]`
+
+## VoiceInTrunkGroup — `GET /v3/voice_in_trunk_groups`
+
+- `filter[external_reference_id]`
+
+## VoiceInTrunk — `GET /v3/voice_in_trunks`
+
+- `filter[configuration.type]`
+- `filter[external_reference_id]`
+- `filter[name]`
+
+## VoiceOutTrunk — `GET /v3/voice_out_trunks`
+
+- `filter[allow_any_did_as_cli]`
+- `filter[authentication_method.type]`
+- `filter[default_did.id]`
+- `filter[default_dst_action]`
+- `filter[external_reference_id]`
+- `filter[media_encryption_mode]`
+- `filter[name]`
+- `filter[name_contains]`
+- `filter[on_cli_mismatch_action]`
+- `filter[status]`
+- `filter[threshold_reached]`
diff --git a/README.md b/README.md
index 8b55b19..1e94303 100644
--- a/README.md
+++ b/README.md
@@ -518,6 +518,8 @@ client.download_export(created.url, "/tmp/export.csv")
 
 ## Filtering, Sorting, and Pagination
 
+> See [`FILTERS.md`](FILTERS.md) for the canonical list of `filter[KEY]` keys accepted by every list endpoint, verified live against the DIDWW API at version `2026-04-16`.
+
 ```python
 from didww.query_params import QueryParams