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mcp-builder

Guide for creating high-quality MCP (Model Context Protocol) servers that enable LLMs to interact with external services through well-designed tools. Use when building MCP servers to integrate external APIs or services, whether in Python (FastMCP) or Node/TypeScript (MCP SDK).

2.21x
Quality

74%

Does it follow best practices?

Impact

93%

2.21x

Average score across 10 eval scenarios

SecuritybySnyk

Passed

No findings from the security scan

Fix and improve this skill with Tessl

tessl review fix ./app/skills/mcp-builder/SKILL.md

The canonical home for this skill is pleaseai/mcp-dev

SKILL.md
Quality
Evals
Security

Quality

Content

56%Weight 40%Scale 1-5

Reviews the quality of instructions and guidance provided to agents. Good implementation is clear, handles edge cases, and produces reliable results.

The skill presents a clear, well-sequenced four-phase workflow with useful concrete commands and URLs, but its progressive disclosure architecture is broken in practice: all four reference guides it defers to are missing from the bundle, leaving the implementation phases as checklists with no executable detail. Conciseness is adequate but padded with rationale sentences and duplicated link lists.

Suggestions

Fix the broken reference paths: the four './reference/*.md' guides (mcp_best_practices.md, node_mcp_server.md, python_mcp_server.md, evaluation.md) do not exist in the bundle — either include them (in a 'references/' directory, the conventional name) or inline the essential implementation patterns so Phase 2 is executable on its own.

Link the existing bundle scripts directly by path (e.g., scripts/evaluation.py, scripts/example_evaluation.xml, scripts/requirements.txt) from Phase 4 instead of only describing them through the missing evaluation guide.

Trim duplicated content: the Reference Files section repeats all links and SDK URLs already given in Phase 1, and the Overview duplicates the frontmatter description verbatim; cut one copy of each and drop the opinion-justification for the TypeScript recommendation.

DimensionReasoningScore

Conciseness

The body is mostly tight, instructional bullets, but contains padding that could be trimmed: the Overview restates the frontmatter description verbatim ('Create MCP (Model Context Protocol) servers that enable LLMs to interact with external services through well-designed tools'), the 'Recommended stack' section includes opinion justification ('AI models are good at generating TypeScript code, benefiting from its broad usage, static typing and good linting tools'), Phase 1.1 explains conceptual rationale ('Performance varies by client...') rather than instructing, and the SDK URLs plus all four reference links are repeated between the Process phases and the Reference Files section. This is anchor 3 ('mostly efficient but includes some unnecessary explanation or could be tightened') rather than 4, since the over-explanation and duplication go beyond minor instances.

3 / 5

Actionability

There is genuinely concrete guidance — 'fetch specific pages with .md suffix (e.g., https://modelcontextprotocol.io/specification/draft.md)', 'npx @modelcontextprotocol/inspector', 'python -m py_compile your_server.py', and a complete evaluation XML example — but the core implementation sections are checklists rather than executable instructions: 'Create shared utilities: API client with authentication, Error handling helpers' and 'Use Zod (TypeScript) or Pydantic (Python)' name tools without any code, deferring actual implementation to reference files that do not exist in the bundle. This matches anchor 3 ('some concrete guidance but incomplete... missing key details') and falls short of anchor 4, which expects concrete code or commands with only minor gaps.

3 / 5

Workflow Clarity

The four-phase workflow (Deep Research → Implementation → Review and Test → Create Evaluations) is clearly sequenced with numbered sub-phases, and Phase 3 provides validation checkpoints ('Run npm run build to verify compilation', 'Verify syntax: python -m py_compile your_server.py', MCP Inspector testing) plus a Phase 3.1 quality review before them. It matches anchor 4 ('clear sequence with most checkpoints present; minor validation gaps') but not anchor 5, since there are no explicit error-recovery feedback loops (e.g., what to do when the build or inspector check fails) and evaluation answers are verified without a stated retry path.

4 / 5

Progressive Disclosure

Scored against the actual bundle structure: the body is well-organized with clearly signaled, one-level-deep references and phase-appropriate load timing ('Load During Phase 2', 'Load During Phase 4'), but every referenced path — './reference/mcp_best_practices.md', './reference/node_mcp_server.md', './reference/python_mcp_server.md', './reference/evaluation.md' — points to a directory that does not exist in the bundle, so the bulk of the intended detailed content is inaccessible. The bundle's actual scripts (scripts/evaluation.py, scripts/connections.py, scripts/example_evaluation.xml) are never linked by path, only alluded to ('Running an evaluation with the provided scripts'). This lands at anchor 3 (structure present but content split is broken/incomplete) rather than 4, where references would be intact with only minor organization gaps; the path spelling './reference/' also deviates from the conventional 'references/' directory.

3 / 5

Total

13

/

20

Passed

Description

82%Weight 40%Scale 1-5

Based on the skill's description, can an agent find and select it at the right time? Clear, specific descriptions lead to better discovery.

A strong description with an explicit 'Use when...' clause covering concrete triggers, good natural keyword coverage including framework names, and a clearly distinct niche. Its only weakness is that capabilities are stated at a domain level ('creating high-quality servers') rather than as multiple concrete actions, and 'high-quality'/'well-designed' add mild evaluative padding.

DimensionReasoningScore

Specificity

The description names the domain ('creating high-quality MCP (Model Context Protocol) servers') and one or two actions — creating servers and integrating 'external APIs or services' — but does not enumerate several specific concrete capabilities the way anchor 4 requires ('Lists several specific actions'). 'High-quality' and 'well-designed tools' are evaluative fluff rather than concrete actions, matching anchor 3 ('Names domain and 1-2 concrete actions, but not comprehensive'); it is above anchor 2 because the domain and the integration action are stated concretely.

3 / 5

Completeness

Both questions are answered explicitly: 'what' is 'Guide for creating high-quality MCP servers that enable LLMs to interact with external services through well-designed tools', and 'when' is a concrete 'Use when building MCP servers to integrate external APIs or services, whether in Python (FastMCP) or Node/TypeScript (MCP SDK)'. This is anchor 5 ('clearly and explicitly answers both what AND when with concrete trigger phrases') — the trigger clause is explicit, not merely implied as in anchor 4.

5 / 5

Trigger Term Quality

Natural keywords a user would say are well covered: 'MCP servers', 'Model Context Protocol', 'building MCP servers', 'integrate external APIs or services', 'Python (FastMCP)', 'Node/TypeScript', 'MCP SDK'. This matches anchor 4 ('Good keyword coverage; a few natural terms missing') — it stops short of anchor 5's comprehensive synonym coverage (e.g., no 'tool server', 'MCP integration', or mention of common phrasings like 'expose an API as tools'), but clearly exceeds anchor 3, which expects missing common variations.

4 / 5

Distinctiveness Conflict Risk

MCP server development is a clear niche with distinct triggers ('MCP', 'Model Context Protocol', 'FastMCP', 'MCP SDK'), and the description would not plausibly fire for unrelated skills like general API development or web app building since it is anchored on the protocol name. It matches anchor 5 ('Clear niche with distinct triggers; minimal conflict risk') and is clearly above anchor 4, which expects overlap with closely related skills.

5 / 5

Total

17

/

20

Passed

Validation

93%

Checks the skill against the spec for correct structure and formatting. All validation checks must pass before discovery and implementation can be scored.

Validation — 15 / 16 Passed

Validation for skill structure

CriteriaDescriptionResult

relative_links

Relative link issues: 10 missing

Warning

Total

15

/

16

Passed

Repository

ZHangZHengEric/Sage

Path

app/skills/mcp-builder/SKILL.md

Reviewed

Table of Contents

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