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feat: add supports_parallel_tool_calls for MCP servers

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Port from openai/codex#17667: MCP servers can now opt-in to parallel
tool execution by setting supports_parallel_tool_calls: true in their
config. This allows tools from the same server to run concurrently
within a single tool-call batch, matching the behavior already available
for built-in tools like web_search and read_file.

Previously all MCP tools were forced sequential because they weren't in
the _PARALLEL_SAFE_TOOLS set. Now _should_parallelize_tool_batch checks
is_mcp_tool_parallel_safe() which looks up the server's config flag.

Config example:
  mcp_servers:
    docs:
      command: "docs-server"
      supports_parallel_tool_calls: true

Changes:
- tools/mcp_tool.py: Track parallel-safe servers in _parallel_safe_servers
  set, populated during register_mcp_servers(). Add is_mcp_tool_parallel_safe()
  public API.
- run_agent.py: Add _is_mcp_tool_parallel_safe() lazy-import wrapper. Update
  _should_parallelize_tool_batch() to check MCP tools against server config.
- 11 new tests covering the feature end-to-end.
- Updated MCP docs and config reference.
This commit is contained in:
Teknium 2026-04-14 17:09:50 -07:00
parent 847d7cbea5
commit 64e7226068
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6 changed files with 263 additions and 2 deletions
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18
website/docs/user-guide/features/mcp.md
View file

@ -105,6 +105,7 @@ Hermes reads MCP config from `~/.hermes/config.yaml` under `mcp_servers`.
| `timeout` | number | Tool call timeout |
| `connect_timeout` | number | Initial connection timeout |
| `enabled` | bool | If `false`, Hermes skips the server entirely |
| `supports_parallel_tool_calls` | bool | If `true`, tools from this server may run concurrently |
| `tools` | mapping | Per-server tool filtering and utility policy |
### Minimal stdio example
@ -409,6 +410,23 @@ Because Hermes now only registers those wrappers when both are true:
This is intentional and keeps the tool list honest.
## Parallel Tool Calls
By default, MCP tools run sequentially — one at a time. If your MCP server exposes tools that are safe to run concurrently (e.g. read-only queries, independent API calls), you can opt-in to parallel execution:
```yaml
mcp_servers:
docs:
command: "docs-server"
supports_parallel_tool_calls: true
```
When `supports_parallel_tool_calls` is `true`, Hermes may execute multiple tools from that server at the same time within a single tool-call batch, just like it does for built-in read-only tools (web_search, read_file, etc.).
:::caution
Only enable parallel calls for MCP servers whose tools are safe to run at the same time. If tools read and write shared state, files, databases, or external resources, review the read/write race conditions before enabling this setting.
:::
## MCP Sampling Support
MCP servers can request LLM inference from Hermes via the `sampling/createMessage` protocol. This allows an MCP server to ask Hermes to generate text on its behalf — useful for servers that need LLM capabilities but don't have their own model access.