Skill prerequisite checks and dependency surfacing

Fixes on record

Merged to main. A stamp counts the issues a fix is linked to.

• #659 feat: skill prerequisites — hide skills with unmet runtime dependencies

  merged to main

  files: CONTRIBUTING.md, agent/prompt_builder.py, skills/apple/apple-notes/SKILL.md, skills/apple/apple-reminders/SKILL.md, skills/apple/imessage/SKILL.md, skills/email/himalaya/SKILL.md, skills/feeds/blogwatcher/SKILL.md, skills/gifs/gif-search/SKILL.md, skills/github/codebase-inspection/SKILL.md, skills/mcp/mcporter/SKILL.md, skills/music-creation/songsee/SKILL.md, skills/productivity/notion/SKILL.md, skills/research/duckduckgo-search/SKILL.md, skills/smart-home/openhue/SKILL.md, tests/agent/test_prompt_builder.py, tests/tools/test_skills_tool.py, tools/skills_tool.py

  Show the diff

  • CONTRIBUTING.md

    @@ -328,6 +328,11 @@ license: MIT
     platforms: [macos, linux]          # Optional — restrict to specific OS platforms
                                        #   Valid: macos, linux, windows
                                        #   Omit to load on all platforms (default)
    +prerequisites:                     # Optional — runtime requirements
    +  env_vars: [MY_API_KEY]           #   Env vars that must be set
    +  commands: [curl, jq]             #   CLI binaries that must be on PATH
    +                                   #   Skills with unmet prerequisites are hidden
    +                                   #   from the system prompt and flagged in skill_view.
     metadata:
       hermes:
         tags: [Category, Subcategory, Keywords]
    @@ -366,6 +371,25 @@ platforms: [windows]          # Windows only
     
     If the field is omitted or empty, the skill loads on all platforms (backward compatible). See `skills/apple/` for examples of macOS-only skills.
     
    +### Skill prerequisites
    +
    +Skills can declare runtime prerequisites via the `prerequisites` frontmatter field. Skills with unmet prerequisites are automatically hidden from the system prompt (the agent won't claim it can use them) and show a clear warning in `skill_view()` telling the agent what's missing.
    +
    +```yaml
    +prerequisites:
    +  env_vars: [TENOR_API_KEY]       # Env vars checked via os.getenv()
    +  commands: [curl, jq]            # CLI binaries checked via shutil.which()
    +```
    +
    +Both sub-fields are optional — declare only what applies. If the field is omitted entirely, the skill is always available (backward compatible).
    +
    +**When to declare prerequisites:**
    +- The skill uses a CLI tool that isn't universally installed (e.g., `himalaya`, `openhue`, `ddgs`)
    +- The skill requires an API key in the environment (e.g., `NOTION_API_KEY`, `TENOR_API_KEY`)
    +- Without these, the skill's commands will fail — not just degrade gracefully
    +
    +See `skills/gifs/gif-search/` and `skills/email/himalaya/` for examples.
    +
     ### Skill guidelines
     
     - **No external dependencies unless absolutely necessary.** Prefer stdlib Python, curl, and existing Hermes tools (`web_extract`, `terminal`, `read_file`).

  • agent/prompt_builder.py

    @@ -170,6 +170,22 @@ def _skill_is_platform_compatible(skill_file: Path) -> bool:
             return True  # Err on the side of showing the skill
     
     
    +def _skill_prerequisites_met(skill_file: Path) -> bool:
    +    """Check if a SKILL.md's declared prerequisites are satisfied.
    +
    +    Returns True (show the skill) when prerequisites are met or not declared.
    +    Returns False when the skill explicitly declares prerequisites that are missing.
    +    """
    +    try:
    +        from tools.skills_tool import _parse_frontmatter, check_skill_prerequisites
    +        raw = skill_file.read_text(encoding="utf-8")[:2000]
    +        frontmatter, _ = _parse_frontmatter(raw)
    +        met, _ = check_skill_prerequisites(frontmatter)
    +        return met
    +    except Exception:
    +        return True
    +
    +
     def build_skills_system_prompt() -> str:
         """Build a compact skill index for the system prompt.
     
    @@ -191,6 +207,9 @@ def build_skills_system_prompt() -> str:
             # Skip skills incompatible with the current OS platform
             if not _skill_is_platform_compatible(skill_file):
                 continue
    +        # Skip skills whose prerequisites (env vars, commands) are unmet
    +        if not _skill_prerequisites_met(skill_file):
    +            continue
             rel_path = skill_file.relative_to(skills_dir)
             parts = rel_path.parts
             if len(parts) >= 2:

  • skills/apple/apple-notes/SKILL.md

    @@ -9,6 +9,8 @@ metadata:
       hermes:
         tags: [Notes, Apple, macOS, note-taking]
         related_skills: [obsidian]
    +prerequisites:
    +  commands: [memo]
     ---
     
     # Apple Notes

  • skills/apple/apple-reminders/SKILL.md

    @@ -8,6 +8,8 @@ platforms: [macos]
     metadata:
       hermes:
         tags: [Reminders, tasks, todo, macOS, Apple]
    +prerequisites:
    +  commands: [remindctl]
     ---
     
     # Apple Reminders

  • skills/apple/imessage/SKILL.md

    @@ -8,6 +8,8 @@ platforms: [macos]
     metadata:
       hermes:
         tags: [iMessage, SMS, messaging, macOS, Apple]
    +prerequisites:
    +  commands: [imsg]
     ---
     
     # iMessage

  • skills/email/himalaya/SKILL.md

    @@ -8,6 +8,8 @@ metadata:
       hermes:
         tags: [Email, IMAP, SMTP, CLI, Communication]
         homepage: https://github.com/pimalaya/himalaya
    +prerequisites:
    +  commands: [himalaya]
     ---
     
     # Himalaya Email CLI

  • skills/feeds/blogwatcher/SKILL.md

    @@ -8,6 +8,8 @@ metadata:
       hermes:
         tags: [RSS, Blogs, Feed-Reader, Monitoring]
         homepage: https://github.com/Hyaxia/blogwatcher
    +prerequisites:
    +  commands: [blogwatcher]
     ---
     
     # Blogwatcher

  • skills/gifs/gif-search/SKILL.md

    @@ -1,9 +1,12 @@
     ---
     name: gif-search
     description: Search and download GIFs from Tenor using curl. No dependencies beyond curl and jq. Useful for finding reaction GIFs, creating visual content, and sending GIFs in chat.
    -version: 1.0.0
    +version: 1.1.0
     author: Hermes Agent
     license: MIT
    +prerequisites:
    +  env_vars: [TENOR_API_KEY]
    +  commands: [curl, jq]
     metadata:
       hermes:
         tags: [GIF, Media, Search, Tenor, API]
    @@ -13,32 +16,43 @@ metadata:
     
     Search and download GIFs directly via the Tenor API using curl. No extra tools needed.
     
    +## Setup
    +
    +Set your Tenor API key in your environment (add to `~/.hermes/.env`):
    +
    +```bash
    +TENOR_API_KEY=[redacted:secret-assignment]
    +```
    +
    +Get a free API key at https://developers.google.com/tenor/guides/quickstart — the Google Cloud Console Tenor API key is free and has generous rate limits.
    +
     ## Prerequisites
     
    -- `curl` and `jq` (both standard on Linux)
    +- `curl` and `jq` (both standard on macOS/Linux)
    +- `TENOR_API_KEY` environment variable
     
     ## Search for GIFs
     
     ```bash
     # Search and get GIF URLs
    -curl -s "https://tenor.googleapis.com/v2/search?q=thumbs+up&limit=5&key=[redacted:google-api-key]" | jq -r '.results[].media_formats.gif.url'
    +curl -s "https://tenor.googleapis.com/v2/search?q=thumbs+up&limit=5&key=${TENOR_API_KEY}" | jq -r '.results[].media_formats.gif.url'
     
     # Get smaller/preview versions
    -curl -s "https://tenor.googleapis.com/v2/search?q=nice+work&limit=3&key=[redacted:google-api-key]" | jq -r '.results[].media_formats.tinygif.url'
    +curl -s "https://tenor.googleapis.com/v2/search?q=nice+work&limit=3&key=${TENOR_API_KEY}" | jq -r '.results[].media_formats.tinygif.url'
     ```
     
     ## Download a GIF
     
     ```bash
     # Search and download the top result
    -URL=$(curl -s "https://tenor.googleapis.com/v2/search?q=celebration&limit=1&key=[redacted:google-api-key]" | jq -r '.results[0].media_formats.gif.url')
    +URL=$(curl -s "https://tenor.googleapis.com/v2/search?q=celebration&limit=1&key=${TENOR_API_KEY}" | jq -r '.results[0].media_formats.gif.url')
     curl -sL "$URL" -o celebration.gif
     ```
     
     ## Get Full Metadata
     
     ```bash
    -curl -s "https://tenor.googleapis.com/v2/search?q=cat&limit=3&key=[redacted:google-api-key]" | jq '.results[] | {title: .title, url: .media_formats.gif.url, preview: .media_formats.tinygif.url, dimensions: .media_formats.gif.dims}'
    +curl -s "https://tenor.googleapis.com/v2/search?q=cat&limit=3&key=${TENOR_API_KEY}" | jq '.results[] | {title: .title, url: .media_formats.gif.url, preview: .media_formats.tinygif.url, dimensions: .media_formats.gif.dims}'
     ```
     
     ## API Parameters
    @@ -47,7 +61,7 @@ curl -s "https://tenor.googleapis.com/v2/search?q=cat&limit=3&key=AIzaSyAyimkuYQ
     |-----------|-------------|
     | `q` | Search query (URL-encode spaces as `+`) |
     | `limit` | Max results (1-50, default 20) |
    -| `key` | API key (the one above is Tenor's public demo key) |
    +| `key` | API key (from `$TENOR_API_KEY` env var) |
     | `media_filter` | Filter formats: `gif`, `tinygif`, `mp4`, `tinymp4`, `webm` |
     | `contentfilter` | Safety: `off`, `low`, `medium`, `high` |
     | `locale` | Language: `en_US`, `es`, `fr`, etc. |
    @@ -67,7 +81,6 @@ Each result has multiple formats under `.media_formats`:
     
     ## Notes
     
    -- The API key above is Tenor's public demo key — it works but has rate limits
     - URL-encode the query: spaces as `+`, special chars as `%XX`
     - For sending in chat, `tinygif` URLs are lighter weight
     - GIF URLs can be used directly in markdown: `![alt](url)`

  • skills/github/codebase-inspection/SKILL.md

    @@ -8,6 +8,8 @@ metadata:
       hermes:
         tags: [LOC, Code Analysis, pygount, Codebase, Metrics, Repository]
         related_skills: [github-repo-management]
    +prerequisites:
    +  commands: [pygount]
     ---
     
     # Codebase Inspection with pygount

  • skills/mcp/mcporter/SKILL.md

    @@ -8,6 +8,8 @@ metadata:
       hermes:
         tags: [MCP, Tools, API, Integrations, Interop]
         homepage: https://mcporter.dev
    +prerequisites:
    +  commands: [npx]
     ---
     
     # mcporter

  • skills/music-creation/songsee/SKILL.md

    @@ -8,6 +8,8 @@ metadata:
       hermes:
         tags: [Audio, Visualization, Spectrogram, Music, Analysis]
         homepage: https://github.com/steipete/songsee
    +prerequisites:
    +  commands: [songsee]
     ---
     
     # songsee

  • skills/productivity/notion/SKILL.md

    @@ -8,6 +8,8 @@ metadata:
       hermes:
         tags: [Notion, Productivity, Notes, Database, API]
         homepage: https://developers.notion.com
    +prerequisites:
    +  env_vars: [NOTION_API_KEY]
     ---
     
     # Notion API

  • skills/research/duckduckgo-search/SKILL.md

    @@ -8,6 +8,8 @@ metadata:
       hermes:
         tags: [search, duckduckgo, web-search, free, fallback]
         related_skills: [arxiv]
    +prerequisites:
    +  commands: [ddgs]
     ---
     
     # DuckDuckGo Search (Firecrawl Fallback)

  • skills/smart-home/openhue/SKILL.md

    @@ -8,6 +8,8 @@ metadata:
       hermes:
         tags: [Smart-Home, Hue, Lights, IoT, Automation]
         homepage: https://www.openhue.io/cli
    +prerequisites:
    +  commands: [openhue]
     ---
     
     # OpenHue CLI

  • tests/agent/test_prompt_builder.py

    @@ -8,6 +8,7 @@
         _scan_context_content,
         _truncate_content,
         _read_skill_description,
    +    _skill_prerequisites_met,
         build_skills_system_prompt,
         build_context_files_prompt,
         CONTEXT_FILE_MAX_CHARS,
    @@ -211,6 +212,69 @@ def test_includes_matching_platform_skills(self, monkeypatch, tmp_path):
             assert "imessage" in result
             assert "Send iMessages" in result
     
    +    def test_excludes_skills_with_unmet_prerequisites(self, monkeypatch, tmp_path):
    +        """Skills with missing env var prerequisites should not appear."""
    +        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
    +        monkeypatch.delenv("MISSING_API_KEY_XYZ", raising=False)
    +        skills_dir = tmp_path / "skills" / "media"
    +
    +        gated = skills_dir / "gated-skill"
    +        gated.mkdir(parents=True)
    +        (gated / "SKILL.md").write_text(
    +            "---\nname: gated-skill\ndescription: Needs a key\n"
    +            "prerequisites:\n  env_vars: [MISSING_API_KEY_XYZ]\n---\n"
    +        )
    +
    +        available = skills_dir / "free-skill"
    +        available.mkdir(parents=True)
    +        (available / "SKILL.md").write_text(
    +            "---\nname: free-skill\ndescription: No prereqs\n---\n"
    +        )
    +
    +        result = build_skills_system_prompt()
    +        assert "free-skill" in result
    +        assert "gated-skill" not in result
    +
    +    def test_includes_skills_with_met_prerequisites(self, monkeypatch, tmp_path):
    +        """Skills with satisfied prerequisites should appear normally."""
    +        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
    +        monkeypatch.setenv("MY_API_KEY", "test_value")
    +        skills_dir = tmp_path / "skills" / "media"
    +
    +        skill = skills_dir / "ready-skill"
    +        skill.mkdir(parents=True)
    +        (skill / "SKILL.md").write_text(
    +            "---\nname: ready-skill\ndescription: Has key\n"
    +            "prerequisites:\n  env_vars: [MY_API_KEY]\n---\n"
    +        )
    +
    +        result = build_skills_system_prompt()
    +        assert "ready-skill" in result
    +
    +
    +# =========================================================================
    +# _skill_prerequisites_met
    +# =========================================================================
    +
    +
    +class TestSkillPrerequisitesMet:
    +    def test_met_or_absent(self, tmp_path, monkeypatch):
    +        """No prereqs, met prereqs, and missing file all return True."""
    +        monkeypatch.setenv("PRESENT_KEY_123", "val")
    +        basic = tmp_path / "basic.md"
    +        basic.write_text("---\nname: basic\ndescription: basic\n---\n")
    +        ready = tmp_path / "ready.md"
    +        ready.write_text("---\nname: ready\ndescription: ready\nprerequisites:\n  env_vars: [PRESENT_KEY_123]\n---\n")
    +        assert _skill_prerequisites_met(basic) is True
    +        assert _skill_prerequisites_met(ready) is True
    +        assert _skill_prerequisites_met(tmp_path / "nope.md") is True
    +
    +    def test_unmet_returns_false(self, tmp_path, monkeypatch):
    +        monkeypatch.delenv("NONEXISTENT_KEY_ABC", raising=False)
    +        skill = tmp_path / "SKILL.md"
    +        skill.write_text("---\nname: gated\ndescription: gated\nprerequisites:\n  env_vars: [NONEXISTENT_KEY_ABC]\n---\n")
    +        assert _skill_prerequisites_met(skill) is False
    +
     
     # =========================================================================
     # Context files prompt builder

  • tests/tools/test_skills_tool.py

    @@ -11,6 +11,7 @@
         _estimate_tokens,
         _find_all_skills,
         _load_category_description,
    +    check_skill_prerequisites,
         skill_matches_platform,
         skills_list,
         skills_categories,
    @@ -464,3 +465,124 @@ def test_multi_platform_skill(self, tmp_path):
             assert len(skills_darwin) == 1
             assert len(skills_linux) == 1
             assert len(skills_win) == 0
    +
    +
    +# ---------------------------------------------------------------------------
    +# check_skill_prerequisites
    +# ---------------------------------------------------------------------------
    +
    +
    +class TestCheckSkillPrerequisites:
    +    def test_no_or_empty_prerequisites(self):
    +        """No field, empty dict, or non-dict all pass."""
    +        assert check_skill_prerequisites({})[0] is True
    +        assert check_skill_prerequisites({"prerequisites": {}})[0] is True
    +        assert check_skill_prerequisites({"prerequisites": "curl"})[0] is True
    +
    +    def test_env_var_present_and_missing(self, monkeypatch):
    +        monkeypatch.setenv("MY_TEST_KEY", "val")
    +        monkeypatch.delenv("NONEXISTENT_TEST_VAR_XYZ", raising=False)
    +        assert check_skill_prerequisites({"prerequisites": {"env_vars": ["MY_TEST_KEY"]}})[0] is True
    +        met, missing = check_skill_prerequisites({"prerequisites": {"env_vars": ["NONEXISTENT_TEST_VAR_XYZ"]}})
    +        assert met is False
    +        assert "env $NONEXISTENT_TEST_VAR_XYZ" in missing
    +
    +    def test_command_present_and_missing(self):
    +        assert check_skill_prerequisites({"prerequisites": {"commands": ["python3"]}})[0] is True
    +        met, missing = check_skill_prerequisites({"prerequisites": {"commands": ["nonexistent_binary_xyz_123"]}})
    +        assert met is False
    +        assert "command `nonexistent_binary_xyz_123`" in missing
    +
    +    def test_mixed_env_and_commands(self, monkeypatch):
    +        monkeypatch.delenv("MISSING_A", raising=False)
    +        met, missing = check_skill_prerequisites({
    +            "prerequisites": {
    +                "env_vars": ["MISSING_A"],
    +                "commands": ["python3", "nonexistent_cmd_xyz"],
    +            }
    +        })
    +        assert met is False
    +        assert len(missing) == 2
    +
    +    def test_string_instead_of_list(self, monkeypatch):
    +        """YAML scalar (string) should be coerced to a single-element list."""
    +        monkeypatch.delenv("SOLO_VAR", raising=False)
    +        assert check_skill_prerequisites({"prerequisites": {"env_vars": "SOLO_VAR"}})[0] is False
    +        assert check_skill_prerequisites({"prerequisites": {"commands": "nonexistent_cmd_xyz_solo"}})[0] is False
    +
    +
    +# ---------------------------------------------------------------------------
    +# _find_all_skills — prerequisites integration
    +# ---------------------------------------------------------------------------
    +
    +
    +class TestFindAllSkillsPrerequisites:
    +    def test_skills_with_unmet_prereqs_flagged(self, tmp_path, monkeypatch):
    +        monkeypatch.delenv("NONEXISTENT_API_KEY_XYZ", raising=False)
    +        with patch("tools.skills_tool.SKILLS_DIR", tmp_path):
    +            _make_skill(
    +                tmp_path, "needs-key",
    +                frontmatter_extra="prerequisites:\n  env_vars: [NONEXISTENT_API_KEY_XYZ]\n",
    +            )
    +            skills = _find_all_skills()
    +        assert len(skills) == 1
    +        assert skills[0]["prerequisites_met"] is False
    +        assert any("NONEXISTENT_API_KEY_XYZ" in m for m in skills[0]["prerequisites_missing"])
    +
    +    def test_skills_with_met_prereqs_no_flag(self, tmp_path, monkeypatch):
    +        monkeypatch.setenv("MY_PRESENT_KEY", "val")
    +        with patch("tools.skills_tool.SKILLS_DIR", tmp_path):
    +            _make_skill(
    +                tmp_path, "has-key",
    +                frontmatter_extra="prerequisites:\n  env_vars: [MY_PRESENT_KEY]\n",
    +            )
    +            skills = _find_all_skills()
    +        assert len(skills) == 1
    +        assert "prerequisites_met" not in skills[0]
    +
    +    def test_skills_without_prereqs_no_flag(self, tmp_path):
    +        with patch("tools.skills_tool.SKILLS_DIR", tmp_path):
    +            _make_skill(tmp_path, "simple-skill")
    +            skills = _find_all_skills()
    +        assert len(skills) == 1
    +        assert "prerequisites_met" not in skills[0]
    +
    +
    +# ---------------------------------------------------------------------------
    +# skill_view — prerequisites warnings
    +# ---------------------------------------------------------------------------
    +
    +
    +class TestSkillViewPrerequisites:
    +    def test_warns_on_unmet_prerequisites(self, tmp_path, monkeypatch):
    +        monkeypatch.delenv("MISSING_KEY_XYZ", raising=False)
    +        with patch("tools.skills_tool.SKILLS_DIR", tmp_path):
    +            _make_skill(
    +                tmp_path, "gated-skill",
    +                frontmatter_extra="prerequisites:\n  env_vars: [MISSING_KEY_XYZ]\n",
    +            )
    +            raw = skill_view("gated-skill")
    +        result = json.loads(raw)
    +        assert result["success"] is True
    +        assert result["prerequisites_met"] is False
    +        assert "MISSING_KEY_XYZ" in result["prerequisites_warning"]
    +
    +    def test_no_warning_when_prereqs_met(self, tmp_path, monkeypatch):
    +        monkeypatch.setenv("PRESENT_KEY", "value")
    +        with patch("tools.skills_tool.SKILLS_DIR", tmp_path):
    +            _make_skill(
    +                tmp_path, "ready-skill",
    +                frontmatter_extra="prerequisites:\n  env_vars: [PRESENT_KEY]\n",
    +            )
    +            raw = skill_view("ready-skill")
    +        result = json.loads(raw)
    +        assert result["success"] is True
    +        assert "prerequisites_warning" not in result
    +
    +    def test_no_warning_when_no_prereqs(self, tmp_path):
    +        with patch("tools.skills_tool.SKILLS_DIR", tmp_path):
    +            _make_skill(tmp_path, "plain-skill")
    +            raw = skill_view("plain-skill")
    +        result = json.loads(raw)
    +        assert result["success"] is True
    +        assert "prerequisites_warning" not in result

  • tools/skills_tool.py

    @@ -34,6 +34,11 @@
         platforms: [macos]            # Optional — restrict to specific OS platforms
                                       #   Valid: macos, linux, windows
                                       #   Omit to load on all platforms (default)
    +    prerequisites:                # Optional — runtime requirements
    +      env_vars: [API_KEY]         #   Env vars that must be set (checked via os.getenv)
    +      commands: [curl, jq]        #   CLI binaries that must be on PATH (checked via shutil.which)
    +                                  #   Skills with unmet prerequisites are hidden from the
    +                                  #   system prompt and flagged with a warning in skill_view.
         compatibility: Requires X     # Optional (agentskills.io)
         metadata:                     # Optional, arbitrary key-value (agentskills.io)
           hermes:
    @@ -65,6 +70,7 @@
     import json
     import os
     import re
    +import shutil
     import sys
     from pathlib import Path
     from typing import Dict, Any, List, Optional, Tuple
    @@ -118,6 +124,43 @@ def skill_matches_platform(frontmatter: Dict[str, Any]) -> bool:
         return False
     
     
    +def check_skill_prerequisites(frontmatter: Dict[str, Any]) -> Tuple[bool, List[str]]:
    +    """Check if a skill's declared prerequisites are satisfied.
    +
    +    Skills declare prerequisites via a top-level ``prerequisites`` dict
    +    in their YAML frontmatter::
    +
    +        prerequisites:
    +          env_vars: [TENOR_API_KEY]
    +          commands: [curl, jq]
    +
    +    Returns:
    +        (all_met, missing) — True + empty list if all met, else False + list
    +        of human-readable descriptions of what's missing.
    +    """
    +    prereqs = frontmatter.get("prerequisites")
    +    if not prereqs or not isinstance(prereqs, dict):
    +        return True, []
    +
    +    missing: List[str] = []
    +
    +    env_vars = prereqs.get("env_vars") or []
    +    if isinstance(env_vars, str):
    +        env_vars = [env_vars]
    +    for var in env_vars:
    +        if not os.getenv(str(var)):
    +            missing.append(f"env ${var}")
    +
    +    commands = prereqs.get("commands") or []
    +    if isinstance(commands, str):
    +        commands = [commands]
    +    for cmd in commands:
    +        if not shutil.which(str(cmd)):
    +            missing.append(f"command `{cmd}`")
    +
    +    return (len(missing) == 0), missing
    +
    +
     def check_skills_requirements() -> bool:
         """Skills are always available -- the directory is created on first use if needed."""
         return True
    @@ -262,12 +305,19 @@ def _find_all_skills() -> List[Dict[str, Any]]:
                     description = description[:MAX_DESCRIPTION_LENGTH - 3] + "..."
                 
                 category = _get_category_from_path(skill_md)
    -            
    -            skills.append({
    +
    +            prereqs_met, prereqs_missing = check_skill_prerequisites(frontmatter)
    +
    +            entry = {
                     "name": name,
                     "description": description,
                     "category": category,
    -            })
    +            }
    +            if not prereqs_met:
    +                entry["prerequisites_met"] = False
    +                entry["prerequisites_missing"] = prereqs_missing
    +
    +            skills.append(entry)
                 
             except Exception:
                 continue
    @@ -635,6 +685,17 @@ def skill_view(name: str, file_path: str = None, task_id: str = None) -> str:
                 "usage_hint": "To view linked files, call skill_view(name, file_path) where file_path is e.g. 'references/api.md' or 'assets/config.yaml'" if linked_files else None
             }
             
    +        # Prerequisite check — warn the agent if requirements are unmet
    +        prereqs_met, prereqs_missing = check_skill_prerequisites(frontmatter)
    +        if not prereqs_met:
    +            result["prerequisites_met"] = False
    +            result["prerequisites_missing"] = prereqs_missing
    +            result["prerequisites_warning"] = (
    +                f"This skill requires {', '.join(prereqs_missing)} which "
    +                f"{'is' if len(prereqs_missing) == 1 else 'are'} not available. "
    +                f"Tell the user what's needed before attempting to use this skill."
    +            )
    +
             # Surface agentskills.io optional fields when present
             if frontmatter.get('compatibility'):
                 result["compatibility"] = frontmatter['compatibility']