opencode keeps only the text parts of an MCP prompt, and fills arguments positionally

Kind: nuance · Status: current · Last verified: 2026-08-24 · Clients: opencode · Revisions: 2025-11-25

opencode surfaces prompts well at the listing level. prompts/list is fully paginated, gated on the server declaring prompts, and every prompt becomes a slash command carrying the server's description.

The loss is in the template. A prompt's messages are flattened by taking the text of each and joining them:

.map((message) => (message.content.type === "text" ? message.content.text : ""))
.join("\n")

A message whose content is an image or an embedded resource contributes an empty string. It is not skipped and not reported — it becomes a blank line in the middle of the template. A prompt built around a diagram or an attached document arrives as its surrounding prose with a hole where the content was, and nothing distinguishes that from a prompt the server wrote with a blank line in it.

Prompt content has allowed image and resource parts since 2024-11-05, so this is not a new part of the spec that clients have yet to catch up with.

Arguments are positional

Arguments are filled by index rather than by name:

Object.fromEntries(prompt.arguments.map((argument, i) => [argument.name, `$${i + 1}`]))

Each declared argument gets the placeholder $1, $2 and so on in declaration order, and the command's hints are the same list. The names the server declared are used as keys but never shown to the user, so invoking a prompt means knowing what the server put first.

This is fine for a one-argument prompt and gets worse as arguments accumulate, particularly where several are optional — there is no way to supply the third without supplying the first two.

Why it is a nuance and not a gap

Nothing here is a spec violation. A client may render a prompt however it likes, and reducing prompts to a text template is a defensible fit for a terminal agent. But a matrix cell reading "prompts: yes" carries the implication that a server's prompts arrive intact, and for any prompt that is not pure text they do not.

Sources