(registered 2026-10-29, last updated 2026-10-29)

Media type name: application

Media subtype name: vnd.pebblestream.psosf+zip

Required parameters: N/A

Optional parameters: N/A

Encoding considerations: binary

A zip archive

Security considerations: An archive contains plain-text CSV and JSON
files and no executable code. Worksheet fields are escaped so that no 
field begins with a character spreadsheet applications evaluate as a 
formula; formulas carry a "psosf:" prefix. Readers must treat 
archives as untrusted: reject path traversal, symbolic links and 
duplicate names, cap entry counts, sizes and compression ratios, and 
reject unescaped fields. Formulas are limited to an allow-list of 
functions, and references to other workbooks, URLs or paths are 
refused. Optional Ed25519 signatures provide integrity and 
provenance, not confidentiality.

Interoperability considerations: The version is given by 
"format-version" in manifest.json; archives without a manifest are 
version 1.0.

Published specification: 

https://docs.pebblestream.com/docs/pebble-stream-open-spreadsheet-format

Applications which use this media: Pebble Stream Zen (Excel and 
Google Sheets add-ins), the Pebble Stream compiler service, and 
Pebble Stream Flow.

Fragment identifier considerations: N/A

Restrictions on usage: No restrictions

Additional information:

1. Deprecated alias names for this type: N/A
2. Magic number(s): 50 4B 03 04
3. File extension(s): psosf
4. Macintosh file type code: N/A
5. Object Identifiers: N/A

Person to contact for further information:

1. Name: Bediako George
2. Email: bediako.george&georgetownsoftware.house

Intended usage: COMMON

Author/Change controller: Georgetown Software House, Inc.