These URLs at are intended to be long-term permalinks.

/address-spec (Special Hostnames in Tor)
/bandwidth-file-spec (Directory Authority Bandwidth File spec)
/bridgedb-spec (BridgeDB specification)
/cert-spec (Ed25519 certificates in Tor)
/collector-protocol (Protocol of CollecTor's File Structure)
/control-spec (Tor control protocol, version 1)
/dir-spec (Tor directory protocol, version 3)
/dir-list-spec (Tor Directory List file format)
/ext-orport-spec (Extended ORPort for pluggable transports)
/gettor-spec (GetTor specification)
/padding-spec (Tor Padding Specification)
/path-spec (Tor Path Specification)
/pt-spec (Tor Pluggable Transport Specification, version 1)
/rend-spec (Tor Onion Service Rendezvous Specification, latest version)
/rend-spec-v2 (Tor Onion Service Rendezvous Specification, Version 2 (Obsolete))
/rend-spec-v3 (Tor Onion Service Rendezvous Specification, Version 3 (Latest))
/socks-extensions (Tor's extensions to the SOCKS protocol)
/srv-spec (Tor Shared Random Subsystem Specification)
/tor-fw-helper-spec (Tor's (little) Firewall Helper specification)
/tor-spec (Tor Protocol Specification)
/torbrowser-design (The Design and Implementation of the Tor Browser)
/version-spec (How Tor Version Numbers Work)
/tor-design (Tor: The Second-Generation Onion Router)
/walking-onions (Walking Onions specifications)