An IANA Registry for Model Context Protocol Tool Surface Names

Status of This Memo

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Table of Contents

1. Introduction

The Model Context Protocol [MCP-SPEC] specifies a wire format for clients (typically agent runtimes) to invoke typed capabilities ("tools") on remote servers. Each tool is addressed by a textual surface name; the server's manifest enumerates the surface names it offers and the JSON Schema of each surface's arguments and return shape.¶

In the absence of a coordinated registry, surface names are chosen ad hoc by server operators. Collisions are common: two operators may both expose a surface named search, with incompatible argument schemas, and a client switching between servers has no machine-readable signal that the two surfaces are not the same capability.¶

[ORGALTER] names four typed surfaces, org_alter_handbook, org_alter_sop_registry, org_alter_enforcement_gates, and org_alter_ingest, as illustrative of its reference substrate. It requests no IANA action, and leaves a registry for canonical surface names to a future revision or a companion specification.¶

This document establishes the registry, defines the per-entry fields and the registration procedure, and registers the four names from [ORGALTER] as the initial contents.¶

2. Terminology

Surface Name

A textual identifier by which an MCP client invokes a typed capability on an MCP server. Surface names are case-sensitive ASCII strings matching the ABNF in Section 3.2.¶

Surface Specification

The document that defines the argument schema, the return shape, the authentication requirements, and the behavioural semantics of a surface name.¶

Operator

The entity responsible for a substrate that exposes one or more MCP servers. An operator is identified by a ~handle per [MCPDNS] when the substrate is recognised under the DNS identity protocol. Written as a URI, that handle is an alter: URI as defined in [ALTER-URI], for example alter:~acme.¶

Vendor Prefix

A common leading substring shared by surface names operated by a single substrate. org_alter_ is the vendor prefix for the reference substrate operated by Alter Meridian Pty Ltd.¶

3. Registry Structure

surface-name = name-component *( "_" name-component )
name-component
             = ALPHA *( ALPHA / DIGIT )

4. Registration Procedure

Registration in this registry SHALL follow the Specification Required policy of [RFC8126] Section 4.6, with the additional provisions below.¶

The Designated Expert pool, appointed by the IESG, evaluates each registration request against the following criteria:¶

1. The proposed surface name conforms to the ABNF in Section 3.2.¶

2. The Specification Reference is stable and publicly retrievable at the time of registration.¶

3. The argument schema and return shape described in the Specification Reference are precise enough to enable interoperable client implementations.¶

4. The Specification Reference states the authentication requirements of the surface; a Specification Reference that leaves them unstated is returned for clarification. The registry does not itself record them.¶

5. The proposed entry does not collide with an existing entry either by exact match or by a vendor-prefix conflict (the proposed name would shadow or be shadowed by an existing entry).¶

The Designated Expert MAY accept, request revision of, or reject a request. Rejected requests are returned with reasons. Accepted requests are entered as Active status when the surface is implemented by a server, and as Provisional status when it is specified but not yet implemented.¶

A registrant MAY request Provisional status pending a stable Specification Reference; provisional entries SHALL be reviewed within twelve months of registration and either promoted to Active, returned to the registrant for revision, or removed.¶

5. Initial Registry Contents

The following entries, the four surfaces of Section 3.1 of [ORGALTER], are registered as the initial contents of the registry. The Vendor prefix of all four is org_alter_ and the Change controller is Alter Meridian Pty Ltd. The alter_ prefix names the canonical handler of each surface, and a name under org_alter_ is an alias of it.¶

org_alter_ingest is served by a deployed server. The other three are specified in [ORGALTER] and have no deployed implementation yet, so they are registered as Provisional and reviewed under Section 4.¶

Further surface names under the org_alter_ vendor prefix are registered through the procedure of Section 4; each request identifies the Specification Reference and change controller for the new surface. No registry-structure amendment is required to admit further entries.¶

6. Operational Considerations

7. Security Considerations

8. IANA Considerations

This document requests that IANA establish a new registry titled "Model Context Protocol Tool Surface Names".¶

• Registry name: Model Context Protocol Tool Surface Names¶

• Registration policy: Specification Required per [RFC8126] Section 4.6, with the Designated Expert criteria of Section 4 of this document.¶

• Per-entry fields: Surface name, Specification reference, Vendor prefix, Change controller, Status, First registered, as defined in Section 3.1 of this document.¶

• ABNF for surface names: As defined in Section 3.2 of this document.¶

• Initial contents: As defined in Section 5 of this document.¶

• Reference: This document.¶

9. Acknowledgements

The registry mechanism is informed by the IANA registry-design guidance of [RFC8126] and by the practice of vendor-prefixed header-field registries in HTTP and DNS-RR-type registries. The initial contents are drawn from [ORGALTER].¶

10. Normative References

[BCP14]

Best Current Practice 14, <https://www.rfc-editor.org/info/bcp14>.
At the time of writing, this BCP comprises the following:

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.

Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8126]

Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.

[MCPDNS]

Morrison, B., "Discovery of Model Context Protocol Servers via DNS TXT Records", 2026, <https://datatracker.ietf.org/doc/draft-morrison-mcp-dns-discovery/>.

[ORGALTER]

Morrison, B., "Policy Provision and Governance Inheritance from an Organisational Identity Substrate", 2026, <https://datatracker.ietf.org/doc/draft-morrison-org-alter-policy-provision/>.

11. Informative References

[ALTER-URI]

Morrison, B., "The 'alter' URI Scheme for Dispatchable ~handle References", 2026, <https://datatracker.ietf.org/doc/draft-morrison-alter-uri-scheme/>.

[MCP-SPEC]

Agentic AI Foundation, "Model Context Protocol Specification", 2026, <https://modelcontextprotocol.io/specification>.

Document History

draft-morrison-mcp-tool-surface-names-registry-02 (October 2026):¶

Removes the Authentication scope field from the per-entry fields, and replaces the Public-Surface Caller Confusion section with Authentication Changes. Re-statuses three of the four initial entries as Provisional, because no deployed server implements them. The remaining changes are editorial.¶

• Corrects the account of [ORGALTER] in the Abstract, Section 1 and Section 5, which said it requests IANA registration of its four surface names. Since its revision 01 it requests no IANA action and gives the names as illustrative of its reference substrate.¶

• Updates the title of the [ORGALTER] reference to the one that document now carries.¶

• Names the Agentic AI Foundation as the author of [MCP-SPEC].¶

• Removes the citations from the Abstract.¶

• Removes the statements about what other drafts assumed and what later drafts will do. Section 5 now points further registrations at Section 4.¶

• States in Section 6.1 that [MCPDNS] discovers the MCP server for the domain under which a ~handle is hosted, where it said for a given ~handle.¶

• Points the Surface Name definition at Section 3.2, where the ABNF is, rather than Section 3, and writes every internal section reference as a cross-reference.¶

• Renames the Change Log appendix to Document History and adds the entry for revision 01.¶

• Notes in the Operator definition that an operator's ~handle, written as a URI, is an alter: URI [ALTER-URI], and adds that informative reference.¶

draft-morrison-mcp-tool-surface-names-registry-01 (August 2026):¶

• Changes the intended status to Informational on the Independent Submission stream.¶

• Removes the Status of This Memo section from the body, the author's postal address, and three references the text did not cite.¶

• Gives the field values shared by the four initial entries once, above a two-column table.¶

• Corrects the internal section references after renumbering.¶

draft-morrison-mcp-tool-surface-names-registry-00 (May 2026):¶

• Initial submission. Establishes the registry, defines the registration procedure, and registers the four initial entries from [ORGALTER].¶

Author's Address