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opa-mcp-server

opa-mcp-server

by OrygnsCode
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TypeScript
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Compile (partially evaluate) a query on OPA

opa_compile_query
Read-onlyIdempotent

Partially evaluate a Rego query using the OPA compile endpoint to return the residual query, revealing what remains unknown after substituting known input.

Instructions

Send a query to the OPA server's /v1/compile endpoint for partial evaluation. Returns the residual query -- what remains after substituting in everything that's known.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "query": "<query>"
    },
    "name": "opa_compile_query"
  }
}

Input Schema

NameRequiredDescriptionDefault
inputNoOptional partial input document.
queryYesRego query to compile, e.g. "data.rbac.allow == true".
unknownsNoRefs to treat as unknown (default: ["input"]).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Addedv0.1.13
  2. Removedv0.1.5
  3. Addedv0.1.2
  4. Removedv0.1.1
  5. First observedv0.1.0

TDQS

A3.8/5.0
Behavior4/5

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

Annotations already provide readOnlyHint=true and idempotentHint=true. The description adds value by specifying the exact HTTP endpoint and explaining the concept of partial evaluation (substituting knowns). This provides behavioral context beyond annotations without contradiction.

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?

Two sentences efficiently deliver the action and result. No extraneous text. The first sentence is front-loaded with the verb 'compile' and endpoint, making it immediately actionable.

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?

The description covers the tool's core behavior and return value (residual query) without an output schema. It assumes familiarity with OPA concepts but is sufficient for an agent. Could add more on use cases or prerequisites, but is adequate for the complexity.

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?

Schema coverage is 100% with clear descriptions for all three parameters. The tool description reinforces the purpose of partial evaluation but does not add new parameter-specific details beyond the schema. Baseline score of 3 is appropriate.

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 sends a query to the OPA server's /v1/compile endpoint for partial evaluation and returns the residual query. This distinguishes it from evaluation tools like rego_eval or opa_query_decision, showing a specific verb and resource.

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

Usage Guidelines2/5

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

The description does not explicitly state when to use this tool vs alternatives such as rego_eval or opa_query_decision. It only mentions partial evaluation but gives no guidance on scenarios or exclusions, leaving the agent to infer usage context from the tool name and siblings.

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

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