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[Bug] MCP prompt arguments receive literal $1/$2 placeholders instead of user input — type validation fails #33564
Description
Description
This error fires at startup, not on interactive use. When opencode discovers an MCP server that exposes prompts with typed arguments (e.g. precision: int), it calls prompts/get during initialization to resolve prompt templates for command registration. The $1/$2 placeholders are sent as literal argument values during this startup probe, and the MCP server's typed argument validation rejects them.
Example error from mcp-mathematics at startup:
MCP error 0: Could not convert argument 'precision' with value '$2' to expected type int
MCP error 0: Could not convert argument 'batch_size' with value '$1' to expected type int
failed to getPrompt
The prompts/get JSON payload confirms the literal placeholder is being sent:
{
"method": "prompts/get",
"params": {
"name": "scientific_calculation",
"arguments": {
"precision": "$2",
"calc_type": "general",
"show_steps": false
}
}
}This was previously reported in #9776 (auto-closed due to inactivity) and confirmed by another user in #9776 (comment) who captured the same "$1" in the prompts/get payload.
The root cause is in packages/opencode/src/command/index.ts lines 100-112. The get template() function maps prompt arguments to $N placeholders but never substitutes them against actual user-provided command arguments before calling mcp.getPrompt().
Plugins
None
OpenCode version
1.14.33
Steps to reproduce
- Configure an MCP server that exposes prompts with typed arguments (e.g.
mcp-mathematicsviauvx mcp-mathematics) - Start opencode
- The error appears in the startup log automatically — no user interaction required
Screenshot and/or share link
N/A
Operating System
Ubuntu 24.04.4 LTS, Linux 6.8.0-124-generic x86_64
Terminal
WezTerm
Full startup log
2026-06-24T00:38:58.314570Z INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:38:58 +1350ms service=mcp clientName=math promptName=scientific_calculation error=MCP error 0: Could not convert argument 'precision' with value '$2' to expected type typing.Annotated[int, 'Decimal precision for results']. Error: 1 validation error for int
2026-06-24T00:38:58.314591Z INFO sidecar: opencode_lib::cli: Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='$2', input_type=str]
2026-06-24T00:38:58.314595Z INFO sidecar: opencode_lib::cli: For further information visit https://errors.pydantic.dev/2.13/v/int_parsing failed to getPrompt
2026-06-24T00:38:58.314908Z INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:38:58 +0ms service=mcp clientName=math promptName=batch_calculation error=MCP error 0: Could not convert argument 'batch_size' with value '$1' to expected type typing.Annotated[int, 'Number of calculations to process']. Error: 1 validation error for int
2026-06-24T00:38:58.314927Z INFO sidecar: opencode_lib::cli: Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='$1', input_type=str]
2026-06-24T00:38:58.314933Z INFO sidecar: opencode_lib::cli: For further information visit https://errors.pydantic.dev/2.13/v/int_parsing failed to getPrompt
2026-06-24T00:38:58.487985Z INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:38:58 +173ms service=server error=Session not found failed
2026-06-24T00:38:59.379392Z INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:38:59 +892ms service=server error=NotFoundError failed
2026-06-24T00:39:06.830627Z INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:39:06 +7451ms service=file.watcher dir=/home/muksihs cause=TimeoutError: TimeoutError
2026-06-24T00:39:06.830645Z INFO sidecar: opencode_lib::cli: at orElse (/$bunfs/root/chunk-y3yhj99w.js:25:15739)
2026-06-24T00:39:06.830648Z INFO sidecar: opencode_lib::cli: at runLoop (/$bunfs/root/chunk-y3yhj99w.js:25:2045)
2026-06-24T00:39:06.830651Z INFO sidecar: opencode_lib::cli: at evaluate (/$bunfs/root/chunk-y3yhj99w.js:25:1435)
2026-06-24T00:39:06.830653Z INFO sidecar: opencode_lib::cli: at <anonymous> (/$bunfs/root/chunk-y3yhj99w.js:25:5589)
2026-06-24T00:39:06.830656Z INFO sidecar: opencode_lib::cli: at FileWatcher.state (/$bunfs/root/chunk-aan3zwa9.js:7:67961)
2026-06-24T00:39:06.830659Z INFO sidecar: opencode_lib::cli: at FileWatcher.state (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:5415)
2026-06-24T00:39:06.830661Z INFO sidecar: opencode_lib::cli: at FileWatcher.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9592)
2026-06-24T00:39:06.830664Z INFO sidecar: opencode_lib::cli: at FileWatcher.init (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:6981)
2026-06-24T00:39:06.830667Z INFO sidecar: opencode_lib::cli: at InstanceBootstrap.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9613)
2026-06-24T00:39:06.830670Z INFO sidecar: opencode_lib::cli: at InstanceBootstrap (/$bunfs/root/chunk-14sjmzy6.js:2722:9779)
2026-06-24T00:39:06.830674Z INFO sidecar: opencode_lib::cli: at InstanceStore.boot (/$bunfs/root/chunk-aan3zwa9.js:18:5242)
2026-06-24T00:39:06.830677Z INFO sidecar: opencode_lib::cli: at InstanceStore.load (/$bunfs/root/chunk-aan3zwa9.js:18:6366) failed to subscribe
2026-06-24T00:39:07.095955Z INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:39:07 +265ms service=file.watcher dir=/home/muksihs/git/opencode-config cause=TimeoutError: TimeoutError
2026-06-24T00:39:07.095979Z INFO sidecar: opencode_lib::cli: at orElse (/$bunfs/root/chunk-y3yhj99w.js:25:15739)
2026-06-24T00:39:07.095984Z INFO sidecar: opencode_lib::cli: at runLoop (/$bunfs/root/chunk-y3yhj99w.js:25:2045)
2026-06-24T00:39:07.095990Z INFO sidecar: opencode_lib::cli: at evaluate (/$bunfs/root/chunk-y3yhj99w.js:25:1435)
2026-06-24T00:39:07.095994Z INFO sidecar: opencode_lib::cli: at <anonymous> (/$bunfs/root/chunk-y3yhj99w.js:25:5589)
2026-06-24T00:39:07.095999Z INFO sidecar: opencode_lib::cli: at FileWatcher.state (/$bunfs/root/chunk-aan3zwa9.js:7:67961)
2026-06-24T00:39:07.096004Z INFO sidecar: opencode_lib::cli: at FileWatcher.state (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:5415)
2026-06-24T00:39:07.096010Z INFO sidecar: opencode_lib::cli: at FileWatcher.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9592)
2026-06-24T00:39:07.096016Z INFO sidecar: opencode_lib::cli: at FileWatcher.init (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:6981)
2026-06-24T00:39:07.096021Z INFO sidecar: opencode_lib::cli: at InstanceBootstrap.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9613)
2026-06-24T00:39:07.096027Z INFO sidecar: opencode_lib::cli: at InstanceBootstrap (/$bunfs/root/chunk-14sjmzy6.js:2722:9779)
2026-06-24T00:39:07.096032Z INFO sidecar: opencode_lib::cli: at InstanceStore.boot (/$bunfs/root/chunk-aan3zwa9.js:18:5242)
2026-06-24T00:39:07.096038Z INFO sidecar: opencode_lib::cli: at InstanceStore.load (/$bunfs/root/chunk-aan3zwa9.js:18:6366) failed to subscribe
2026-06-24T00:39:17.098010Z INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:39:17 +10002ms service=file.watcher dir=/home/muksihs/git/opencode-config/.git cause=TimeoutError: TimeoutError
2026-06-24T00:39:17.098031Z INFO sidecar: opencode_lib::cli: at orElse (/$bunfs/root/chunk-y3yhj99w.js:25:15739)
2026-06-24T00:39:17.098034Z INFO sidecar: opencode_lib::cli: at runLoop (/$bunfs/root/chunk-y3yhj99w.js:25:2045)
2026-06-24T00:39:17.098037Z INFO sidecar: opencode_lib::cli: at evaluate (/$bunfs/root/chunk-y3yhj99w.js:25:1435)
2026-06-24T00:39:17.098039Z INFO sidecar: opencode_lib::cli: at <anonymous> (/$bunfs/root/chunk-y3yhj99w.js:25:5589)
2026-06-24T00:39:17.098042Z INFO sidecar: opencode_lib::cli: at FileWatcher.state (/$bunfs/root/chunk-aan3zwa9.js:7:67961)
2026-06-24T00:39:17.098045Z INFO sidecar: opencode_lib::cli: at FileWatcher.state (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:5415)
2026-06-24T00:39:17.098048Z INFO sidecar: opencode_lib::cli: at FileWatcher.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9592)
2026-06-24T00:39:17.098051Z INFO sidecar: opencode_lib::cli: at FileWatcher.init (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:6981)
2026-06-24T00:39:17.098054Z INFO sidecar: opencode_lib::cli: at InstanceBootstrap.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9613)
2026-06-24T00:39:17.098057Z INFO sidecar: opencode_lib::cli: at InstanceBootstrap (/$bunfs/root/chunk-14sjmzy6.js:2722:9779)
2026-06-24T00:39:17.098060Z INFO sidecar: opencode_lib::cli: at InstanceStore.boot (/$bunfs/root/chunk-aan3zwa9.js:18:5242)
2026-06-24T00:39:17.098066Z INFO sidecar: opencode_lib::cli: at InstanceStore.load (/$bunfs/root/chunk-aan3zwa9.js:18:6366) failed to subscribe
2026-06-24T00:39:32.143253Z INFO opencode_lib: Received Exit
2026-06-24T00:39:32.143269Z INFO opencode_lib: Killed server
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koch-c commentedon Aug 13, 2026
I have also experienced that opencode passes $1, $2, $X... literals to MCP prompts when they are fetched with prompts/get. The MCP server logs the passed arguments as $X and it seems it never receives the actual parameter values given by the user.
neriousy commentedon Oct 1, 2026
In OpenCode v2, MCP prompts are only listed at startup;
prompts/getisn't called then. It runs when you invoke the prompt as a command, using the arguments parsed from what you typed (missing ones are sent as empty strings). Literal$1/$2placeholders are no longer sent.Changed in the v2 MCP command rewrite (#34849).
Closing as completed. If something doesn't work on v2, please open a new issue.
Support OpenCode V1 prompt placeholders