Action
A connection from a Custom GPT to an outside service, defined by an API schema. Does not transfer in OpenAI's plugin migration.
Plugin
Per OpenAI, an installable package that can contain skills, an MCP server, or both.
Skill
Per OpenAI, a folder with a SKILL.md file that describes when and how to run a repeatable workflow. Your GPT's instructions become a skill.
MCP server
A server that exposes tools to a model, with input and output schemas and authentication. A way to rebuild Actions.
Knowledge file
A document you upload so the assistant can refer to it. Becomes a reference file in a migrated skill.
System prompt (instructions)
The standing text that tells the assistant its role and rules.
RAG (retrieval-augmented generation)
Finding relevant passages from your documents at question time and giving them to the model. See RAG vs fine-tuning.
API key
A secret that lets software use a model provider. Never share it or put it in public pages.
Check your GPT before you move it
Paste your instructions, file names and Actions schema into the free checker. It runs in your browser and builds a portable bundle. Nothing is uploaded.
Open the free checkerRelated guides
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