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Cloud (hosted) skills are available on accounts where the feature has been enabled — they are part of a project’s environments, alongside MCP servers and Computers. Local skills, read from your filesystem, need no account feature and always work.
Skills are an open format that provide instructions on how to use MCP tools and complete workflows. MCPJam lets you discover skills from your filesystem (local) or your project (hosted), upload new ones, and use them in the Playground — either automatically based on the user’s prompt or deterministically with the / command.

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Getting Started

  1. Open the Connect view in MCPJam Inspector and select the Skills tab (Servers | Client | Computer | Skills)
  2. Load skills — MCPJam automatically discovers skills from supported directories. You can also upload skills directly through the Skills tab, or run npx skills to install them
  3. Use skills in the Playground — the LLM discovers them automatically, or you can inject them with the / command

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Skill Directories

MCPJam scans the following directories for skills. Each subdirectory is expected to contain a SKILL.md file. When duplicate skill names are found, the first match in search order wins. Global:
Project-local:
If you have no skills installed, run npx skills to get started quickly.

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Uploading Skills

You can upload skill folders directly from the Skills tab in the Connect view. The upload dialog supports drag-and-drop or file browsing and validates the SKILL.md frontmatter in real time.
  • Local: Uploaded skills are stored in ~/.mcpjam/skills/.
  • Hosted (cloud): Cloud skills are SKILL.md-only. Folders that contain files other than SKILL.md are rejected — inline any content that SKILL.md references directly into the file before uploading.
Uploading a skill with a name that already exists will be rejected. Delete the existing skill first if you need to replace it.

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Updating Skills

To pull the latest version of the mcp-inspector skill — which contains MCPJam’s guidance for interpreting probe, doctor, OAuth, and conformance output — run:
To update every installed skill at once:

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Using Skills

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Progressive Disclosure

When you have skills available, MCPJam inlines the skill catalog — each skill’s name and a one-line description — directly into the LLM’s system prompt. The LLM decides which skills are relevant to your prompt and calls loadSkill to load only the full instructions it needs. Once a skill is loaded, the LLM can also browse and read its supporting files using listSkillFiles and readSkillFile. The catalog is not a tool call. There is no general listSkills tool — a turn with no skills gets no skill tools and no catalog section at all, so an empty project never spends a discovery turn on tools that would return nothing.

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Catalog Size Limit

The catalog is capped at 2% of the model’s context window (MCPJam follows OpenAI’s plugin guidance here, measured in characters at roughly 4 characters per token). When a model definition carries no context length, the cap falls back to 8,000 characters. If your skills do not fit, MCPJam shortens descriptions first, and only omits whole skills as a last resort. An omission is always reported in the catalog itself:
An omitted skill is invisible to the model and cannot be loaded, so keep skill descriptions to a single line if you have many skills installed.

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Catalog Fetch Failures (Hosted)

In the hosted app, the catalog is fetched from your project when the prompt is built, with a 3 second timeout. If that fetch fails or times out, the turn proceeds with no skills rather than failing — the LLM sees no catalog and no skill tools. MCPJam records the failure separately from a genuinely empty project, so a run that silently lost its skills is distinguishable after the fact.

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Deterministic Injection

Type / in the input to open the skills popover. Select a skill to inject it directly into the conversation — this pre-loads the SKILL.md content before the LLM processes your message, so the skill is guaranteed to be used. When you select a skill via /, it appears as a card above the input. You can expand the card to browse the skill’s file tree and optionally select additional files to include. Only files you explicitly select are pre-loaded — by default, only the SKILL.md is injected. The / picker works in both local and hosted modes. In the hosted app, it lists your project’s cloud skills.

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LLM Tool Integration

When at least one skill is available, the LLM is given loadSkill, and — on surfaces that can serve supporting files — the two file tools as well: The file tools are not advertised everywhere, because promising them for skills that have no files invites the model to go looking:
  • Local and hosted Playground chat — all three tools.
  • Eval runs with pinned skills — loadSkill only. Pinned eval skills are SKILL.md-only, so there are no files to browse.
  • Environment-resolved turns — all three, but only when the resolved set actually contains a file-bearing skill.
Together with the inlined catalog, these tools let the LLM progressively load skill content as needed during a conversation, rather than injecting every skill’s content upfront.
listSkills is not a general discovery tool. It appears only when a connected MCP server provides skills through the Skills over MCP extension (SEP-2640), and it lists those server-provided skills only — their catalog is fetched from the server on demand rather than inlined in the prompt.