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MCP API Engineering Lab

by joseant1215

MCP API Engineering Lab

Servidor MCP público y genérico para demostrar cómo un agente puede recibir contexto desde una base de datos y contratos OpenAPI.

Creado desde cero para el portafolio. No contiene código, endpoints, reglas, esquemas ni credenciales de clientes.

Stack

  • TypeScript

  • MCP TypeScript SDK v2

  • Zod

  • PostgreSQL (pg)

  • OpenAPI YAML

Related MCP server: openapi-mcp-proxy

Architecture

flowchart LR
    DB[(PostgreSQL)] --> MCP[MCP Server]
    OpenAPI[OpenAPI contracts] --> MCP
    MCP --> Agent[MCP-capable AI client]
    Agent --> Code[Code / API tasks]

Tools

  • get_database_schema

  • list_api_contracts

  • get_api_contract

  • create_api_contract

  • update_api_contract

  • delete_api_contract

Ejecutar

npm install
npm run build
npm start

Para desarrollo:

npm run dev

Base de datos

Si defines DATABASE_URL, el tool get_database_schema consulta information_schema.

Si no está definida, devuelve data/sample-schema.sql, para poder demostrar el servidor sin infraestructura externa.

OpenAPI

Los contratos viven en contracts/.

El MCP puede leer, crear, actualizar y eliminar contratos locales. template.yaml está protegido.

Cliente MCP

Configura este proyecto como servidor stdio con:

node /ruta/al/repositorio/dist/index.js

Usa la documentación de tu cliente MCP para el formato exacto de configuración.

Available Tools

6 tools
create_api_contractB

Create a new minimal OpenAPI 3.1 contract in the local contracts folder.

ParametersJSON Schema
NameRequiredDescriptionDefault
nameYes
titleYes
versionNo1.0.0

TDQS

B3.1/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description bears full responsibility for behavioral disclosure. It only mentions the action and location, omitting important details such as whether existing contracts are overwritten, what 'minimal' entails, required fields, and whether any output is returned. This is a significant gap for a state-changing tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence that front-loads the primary action and object. It contains no redundant filler and is well-structured for quick scanning.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given that there are no annotations, no output schema, and a low-parameter count, the description is far too thin. It does not explain the minimal contract's structure, file format, naming conventions, or behavior on conflicts, leaving many essential details unaddressed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters1/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 0%, meaning the description must compensate for the lack of parameter explanations. It does not mention 'name', 'title', or 'version' at all, leaving the agent to guess their meanings and how they map to the OpenAPI contract.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's function with a specific verb ('Create'), a well-defined resource ('OpenAPI 3.1 contract'), and a location ('local contracts folder'). It distinguishes itself from sibling tools (update, delete, get, list) by focusing on the creation action.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when to use the tool (when creating a new contract) but provides no explicit guidance on when not to use it or how it compares to alternatives. Sibling names make the differentiation inferable, but the description itself does not state exclusions or prerequisites.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

delete_api_contractA

Delete a local OpenAPI contract. The base template is protected.

ParametersJSON Schema
NameRequiredDescriptionDefault
nameYes

TDQS

A3.6/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the burden of disclosing behavior. It does state that the base template is protected, which is a meaningful constraint, but it does not mention whether deletion is permanent, irreversible, or requires any special permissions. This is partially transparent but lacks full destructive-operation disclosure.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is extremely concise: two short sentences with no filler. It front-loads the primary purpose and adds one important constraint, so every word earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple one-parameter delete tool, the description covers the main purpose and a key restriction, but it lacks details about the parameter's meaning, success/failure behavior, and whether deletion is reversible. With no output schema and no annotations, the description is adequate but not complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema has one required parameter 'name' with zero description coverage. The tool description does not clarify what the name refers to or how it maps to a contract, leaving the agent to infer that it is the contract identifier. Since the description does not compensate for the schema gap, this is below the baseline.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses a specific verb ('Delete') and resource ('local OpenAPI contract'), clearly distinguishing it from sibling tools like get_api_contract, create_api_contract, and update_api_contract. The qualifier 'local' adds scope and prevents ambiguity about whether a remote or stored contract is being removed.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies this tool is for removing a local OpenAPI contract, but it does not explicitly say when to prefer it over alternatives or mention exclusions beyond the protected base template. The phrase 'The base template is protected' gives a limited when-not-to-use signal, but no alternatives are named.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

get_api_contractB

Read an OpenAPI contract from the local contracts folder.

ParametersJSON Schema
NameRequiredDescriptionDefault
nameYes

TDQS

B3.4/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries full responsibility for behavioral disclosure. It only states 'Read' which implies a non-destructive operation, but it does not disclose what happens if the contract is missing, whether any side effects occur, or if special permissions are needed. The description is too minimal to provide meaningful transparency.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, front-loaded sentence with no filler. It conveys the core action, resource, and location efficiently. Every word contributes to understanding the tool's purpose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple 1-parameter read tool, the description provides a basic understanding but lacks details about the return value or error behavior. There is no output schema, so the description should indicate what is returned (e.g., the contract contents). It falls short of being fully complete but is adequate for a straightforward read operation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema has one required parameter 'name' with no description (0% coverage). The description does not explicitly explain that 'name' refers to the contract's identifier or file name, though it is implied by the tool's purpose. Since schema coverage is 0%, the description must compensate, but it adds no explicit parameter semantics beyond what is inferable.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's function: 'Read an OpenAPI contract from the local contracts folder.' It identifies a specific verb ('Read'), a resource ('OpenAPI contract'), and a location ('local contracts folder'). This distinguishes it from siblings like 'list_api_contracts' (which lists) or 'get_database_schema' (which targets a different resource type).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage: if you need to read a specific OpenAPI contract by name, this is the tool. However, it provides no explicit guidance on when to use this versus 'list_api_contracts' to find names, or mentions any prerequisites or exclusions. The context is clear but not elaborated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

get_database_schemaA

Read a PostgreSQL schema from DATABASE_URL. Falls back to a local sample schema when no database is configured.

ParametersJSON Schema
NameRequiredDescriptionDefault
tableNo

TDQS

A3.5/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description must disclose behavioral details on its own. It reveals the source (DATABASE_URL) and the fallback to a local sample schema, but leaves ambiguity about what happens if the database is configured but unreachable, and does not describe the output format.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single well-structured sentence that front-loads the primary action and adds the fallback as a secondary clause. It contains no redundant information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool lacks an output schema and annotations, so the description must explain what the tool returns and how the optional parameter affects it. It does neither, leaving the agent with insufficient information for confident invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters1/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has one optional parameter 'table' with no description, and the tool description does not mention it at all. With schema description coverage at 0%, the description should compensate but fails to provide any meaning for the parameter.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description specifies the action 'Read' and the resource 'PostgreSQL schema from DATABASE_URL', making the tool's purpose unambiguous. It also states the fallback behavior, which clearly differentiates it from the sibling API contract tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when to use the tool (when needing a PostgreSQL schema from DATABASE_URL) and mentions fallback behavior when no database is configured. However, it does not explicitly list alternatives or exclusion cases, so it stops short of a 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

list_api_contractsA

List local OpenAPI YAML contracts available in the lab.

ParametersJSON Schema
NameRequiredDescriptionDefault

No parameters

TDQS

A4/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full burden. 'List' clearly implies a read-only operation with no side effects, and the scope is specified. However, it does not disclose output format, error behavior, or whether any filters are possible, but for a simple zero-param list tool this is acceptable.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single sentence, front-loaded with the verb, and contains no fluff. Every word earns its place, making it highly concise and well-structured.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple list tool with no parameters, no annotations, and no output schema, the description provides the essential information: what is listed, where, and in what format. It lacks explicit return-value details, but given the simplicity, the context is sufficiently complete for an agent to select and invoke it.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool has zero parameters, so the schema coverage is vacuously 100%. The description doesn't need to explain parameters. Baseline for 0 params is 4, and nothing in the description detracts from that.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses a specific verb ('List') with a clear resource ('local OpenAPI YAML contracts') and scope ('available in the lab'). It is distinct from siblings like get_api_contract or delete_api_contract, which likely target individual contracts.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage: use this tool to enumerate all available contracts. However, it does not explicitly mention when not to use it or contrast it with get_api_contract or other sibling tools, leaving usage guidance implicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

update_api_contractB

Update the title or version of an existing local OpenAPI contract.

ParametersJSON Schema
NameRequiredDescriptionDefault
nameYes
titleNo
versionNo

TDQS

B3.4/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description must disclose behavioral implications. It states that the tool updates title/version but does not mention whether it modifies the file in place, what happens if the contract name does not exist, whether changes are reversible, or if other fields are preserved. This leaves the agent without critical mutation context.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, focused sentence with no redundant information. It conveys the core purpose efficiently, which is appropriate for a straightforward update tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a mutation tool with no annotations, no output schema, and minimal parameter documentation, this description is too sparse. It omits return values, error behavior, and important usage constraints, leaving significant gaps for an agent to invoke it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 0% description coverage, so the description must compensate. It does clarify that 'title' and 'version' are the update targets and 'name' identifies the existing contract. However, it does not explain that title and version are optional (only name is required), nor does it specify any constraints or the need to provide at least one update field.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly identifies the tool as an update operation ('Update') on a specific resource ('existing local OpenAPI contract') and specifies the fields involved ('title or version'). This distinguishes it from sibling tools like create_api_contract and delete_api_contract.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The word 'existing' implies this is for contracts that already exist, providing some context that this is not for new contracts. However, there is no explicit guidance on when to choose this over create/delete, nor any exclusions or alternative tool names.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

TDQS

A3.7/5.0
Disambiguation5/5

Each tool has a clearly distinct purpose: get_database_schema retrieves schema, while the other five perform CRUD on API contracts. List, get, create, update, and delete are unambiguous.

Naming Consistency5/5

All tools follow a consistent verb_noun pattern (list_, get_, create_, update_, delete_), and get_database_schema fits the same style. No mixed conventions.

Tool Count5/5

Six tools is well within the ideal range for a focused server. Each tool serves a clear purpose without unnecessary overlap or bloat.

Completeness4/5

The CRUD lifecycle for API contracts is fully covered (list, get, create, update, delete). However, update only modifies title/version, not arbitrary fields, and a validation tool is absent—minor gaps for full contract management.

Maintenance

ActivityMaintained
ResponsivenessNo issues

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