Short answer: to give a team a reusable assistant without writing software, use Claude Projects or ChatGPT Projects / Custom GPTs: shared instructions plus a curated set of files. Choose a Custom GPT when you need to share it widely or call an external API through Actions; choose a Project when the assistant is for a team working on the same body of knowledge.
Agent tooling changes fast. Commands and file formats below match the versions current at the time of writing; check the official docs for your version before relying on them.
Side by side
| Need | Claude Projects | ChatGPT Projects | Custom GPTs |
|---|---|---|---|
| Shared instructions | Yes | Yes | Yes |
| Knowledge files | Yes (project knowledge) | Yes | Yes |
| Call external APIs | Through connectors (MCP) | Through connectors/apps | Actions (OpenAPI schema) |
| Share beyond your team | Within your organization | Within your workspace | Link or GPT store, depending on settings |
| Best for | Deep work on one body of knowledge | Ongoing work with history and files | A focused tool many people use |
An instructions template that works in both
instructions.md
# Role
You help the platform team answer questions about our AWS environment.
# Sources
Answer from the attached runbooks and architecture docs first.
If the answer is not in them, say so, then give general guidance
clearly labelled as general.
# Format
- Start with the answer in 2-3 sentences.
- Then steps or commands in code blocks.
- Cite the document name for every fact taken from the files.
# Never
- Invent account IDs, resource names or limits.
- Suggest disabling security controls as a fix.Curate the knowledge, do not dump it
- Upload the 10 to 30 documents people actually need, not the whole wiki.
- One topic per file, with a date and an owner (see how to organize a knowledge base for AI).
- Replace files when the source changes; old copies produce old answers.
Files uploaded to a shared assistant are visible to the people who can use it, in one way or another. Follow your AI usage policy for what may be uploaded.