Does deepagentsjs support skills and system prompts?

Does this have:

1. Support for skills
2. Come with a default systemPrompt? If i send one, does it fully override? Or append?

Here's a thorough answer to both questions:

---

##1. Skills Support — ✅ Yes, extensively

The repo has first-class skills support, built around the Agent Skills specification. There are two layers:

###a) Skills Middleware (src/middleware/skills.ts)

A backend-agnostic middleware that loads skills from configurable sources (paths in a backend). Skills are directories containing a SKILL.md file with YAML frontmatter (name, description) and markdown instructions. Sources are layered — later sources override earlier ones by skill name (last one wins), enabling base → user → project → team skill layering.

You can use it in two ways:

// Option 1: Pass `skills` directly to createDeepAgent
const agent = createDeepAgent({
  skills: ["/skills/user/", "/skills/project/"],
});

// Option 2: Use the middleware explicitly
const middleware = createSkillsMiddleware({
  backend: new FilesystemBackend({ rootDir: "/" }),
  sources: ["/skills/user/", "/skills/project/"],
});
const agent = createDeepAgent({ middleware: [middleware] });

Skills follow a progressive disclosure pattern: the agent sees the skill name + description in its system prompt, but only reads the full SKILL.md instructions (via read_file) when the task matches.

###b) Skills Loader (src/skills/loader.ts)

A lower-level module for directly listing and parsing skills from the filesystem. Exports listSkills, parseSkillMetadata, etc.

###c) Subagent skill inheritance

Custom subagents do not inherit the main agent's skills. They must declare their own skills array. Only the built-in general-purpose subagent inherits the main agent's skills.

###d) Example skills

The repo ships with example skills in examples/skills/: arxiv-search, file-organizer, langgraph-docs, skill-creator, and web-research.

---

##2. System Prompt — ✅ Has a default, and your prompt gets prepended (not replaced or appended)

###The default

There's a BASE_PROMPT defined at agent.ts:45:

const BASE_PROMPT = `In order to complete the objective that the user asks of you, you have access to a number of standard tools.`;

###When you send a systemPrompt

It does not fully override, and it does not simply append. Your prompt goes first, then the BASE_PROMPT is appended after it. Here's the exact logic (agent.ts:118-133):

const finalSystemPrompt = systemPrompt
  ? typeof systemPrompt === "string"
    ? `${systemPrompt}\n\n${BASE_PROMPT}`       // your prompt + base
    : new SystemMessage({
        content: [
          { type: "text", text: BASE_PROMPT },   // base first in content blocks
          ...(typeof systemPrompt.content === "string"
            ? [{ type: "text", text: systemPrompt.content }]
            : systemPrompt.content),
        ],
      })
  : BASE_PROMPT;                                  // no custom prompt → just base

So the behavior depends on the type:

Bottom line: You cannot fully override the base prompt — it will always be included alongside yours. If you need to fully replace it, you'd need to bypass createDeepAgent and call createAgent directly.