What
Catalog validation gained errors and warnings for fetch credentials: an entry using headersHelper must inline its full manifest or the helper will not be run, headers/headersHelper on non-archive sources warn as ineffective, and an archive fetched with a helper but no sha256 warns.
Details
- Routing and identity headers are reported as dropped at download time rather than silently discarded.
Evidence
An entry with headersHelper must inline its full manifest
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up sha256, on Troubleshoot federated cloud access.
* **A large request to a service other than S3 with no content hash.** When a request has no `x-amz-content-sha256` header, Agent Proxy hashes the body before signing and refuses a body over 1 MB (1,048,576 bytes). The AWS CLI and SDKs add…claude-tag/admins/federated-access/troubleshooting see the edit
Added since
A small documentation edit on extended-thinking touched a line naming headers after this was published.
On Claude Opus 4.5, Claude Sonnet 4.5, and earlier Claude 4 models, add the `interleaved-thinking-2025-05-14` [beta header](https://platform.claude.com/docs/en/api/beta-headers) to your API request.build-with-claude/extended-thinking see the edit
Confirmed since
Anthropic's documentation has since written up headers, on MCP, plugins, skills, and hooks.
| `.mcp.json` | MCP servers bundled with this plugin. A JSON object keyed by server name: `{"mcpServers": {"<name>": {"type": "http", "url": "...", "oauth": true}}}`. A remote entry uses `type` (`http` or `sse`), not `transport`, and suppo…third-party/claude-desktop/extensions see the edit
Confirmed since
Anthropic's documentation has since written up headersHelper, on MCP, plugins, skills, and hooks.
| `.mcp.json` | MCP servers bundled with this plugin. A JSON object keyed by server name: `{"mcpServers": {"<name>": {"type": "http", "url": "...", "oauth": true}}}`. A remote entry uses `type` (`http` or `sse`), not `transport`, and suppo…third-party/claude-desktop/extensions see the edit
Two sources agreeTwo things we can check say the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up headersHelper, on MCP, plugins, skills, and hooks.
Anthropic's release notes agree
Plugin marketplaces: headersHelper on a url marketplace or a catalog entry runs a command that mints HTTP headers (e.g. a short-lived token)…