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opa-mcp-server

opa-mcp-server

by OrygnsCode
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Read data from OPA

opa_get_data
Read-onlyIdempotent

Retrieve a value from OPA's data hierarchy by specifying a dotted or slash-separated path. Use literal segments when keys contain both dots and slashes.

Instructions

Read a path from OPA's data hierarchy. A path is read as dotted (users.alice) unless it contains a slash, in which case slash is the only separator (users/alice), so a key such as example.com is addressable as hosts/example.com. Pass segments instead when a key contains both.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "opa_get_data"
  }
}

Input Schema

NameRequiredDescriptionDefault
pathNoData path under `data.`, e.g. "users" or "users/alice".
segmentsNoPath as literal key segments, e.g. ["labels", "app.kubernetes.io/name"]. Use instead of `path` when a key contains a dot or a slash.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.5.0
    • addedInput schema / properties / segments
      Added value: +{
+  "description": "Path as literal key segments, e.g. [\"labels\", \"app.kubernetes.io/name\"]. Use instead of `path` when a key contains a dot or a slash.",
+  "items": {
+    "minLength": 1,
+    "type": "string"
+  },
+  "minItems": 1,
+  "type": "array"
+}
    • removedInput schema / required
      Removed value: -[
-  "path"
-]
  2. Addedv0.1.13
  3. Removedv0.1.5
  4. Addedv0.1.2
  5. Removedv0.1.1
  6. First observedv0.1.0

TDQS

A4.3/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds valuable behavioral detail about path interpretation: dotted notation versus slash-only separator, and how a key containing a dot can still be addressed. This goes beyond what annotations and schema alone provide.

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 three tightly written sentences with no filler. The core action is front-loaded, and the necessary path-format nuances are packed efficiently into the remaining sentences.

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 low-complexity read tool with strong annotations, the description is nearly complete. It covers the trickiest part: path formatting and segments selection. A minor gap is that it does not state what happens when neither `path` nor `segments` is provided, even though the schema allows zero required parameters.

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

Parameters5/5

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

With 100% schema description coverage, the baseline is 3, but the description substantially enriches parameter understanding. It clarifies the dotted-path rule, the slash-only fallback, the `example.com` addressing case, and the exact condition for using `segments` instead of `path`. This resolves real ambiguity in how to invoke the tool.

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 opens with 'Read a path from OPA's data hierarchy,' which names a specific verb, resource, and scope. This clearly differentiates it from siblings like opa_get_policy (policies) and opa_query_decision (decision evaluation) by targeting the data hierarchy specifically.

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 gives strong internal guidance on when to use `path` vs `segments`, but it never names alternative tools or states when this tool should be preferred over opa_get_policy or opa_query_decision. Tool-selection context is implied by 'data hierarchy' but not made explicit.

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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