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Describe Rego policy

rego_describe_policy
Read-onlyIdempotent

Parse a Rego policy into a structured summary of its package, imports, and rules, including clause counts, defaults, args, body length, and annotations. Use it first to understand what a policy does.

Instructions

Parse a Rego policy and return a structured summary: package, imports, and rules. Each rule reports clauseCount (how many definitions share the name), isDefault (true if any clause is a default), hasArgs, bodyLength (total body expressions across all clauses), and inline annotations. Useful as the first step in any "what does this policy do" workflow.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
sourceYesRego source to describe.
v0CompatibleNoRead the policy as Rego v0 (`--v0-compatible`), the syntax OPA used before 1.0: rules without `if`, partial sets as `deny[msg] { ... }`. Needed for a policy that has not been migrated, which OPA 1.x otherwise refuses to load. Where the tool also takes a query, the query is read as v0 too, with the future keywords imported so `in`, `every` and `some x in` still work in it.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.8.0
    • addedInput schema / properties / v0Compatible
      Added value: +{
+  "description": "Read the policy as Rego v0 (`--v0-compatible`), the syntax OPA used before 1.0: rules without `if`, partial sets as `deny[msg] { ... }`. Needed for a policy that has not been migrated, which OPA 1.x otherwise refuses to load. Where the tool also takes a query, the query is read as v0 too, with the future keywords imported so `in`, `every` and `some x in` still work in it.",
+  "type": "boolean"
+}
  2. Addedv0.1.13
  3. Removedv0.1.5
  4. Addedv0.1.2
  5. Removedv0.1.1
  6. First observedv0.1.0

TDQS

A3.7/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered; the description adds valuable context by spelling out the exact report structure (clauseCount, isDefault, hasArgs, bodyLength, inline annotations). It does not mention error behavior for malformed source, a minor gap.

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

Conciseness4/5

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

Three front-loaded sentences: purpose first, then return-field detail, then a usage cue. The field enumeration is dense but each clause earns its place by clarifying output for a tool without an output schema.

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?

With no output schema, the description usefully documents return shape and both parameters are covered by the schema, so an agent has enough to call it correctly. It lacks explicit sibling routing, which is the main missing piece.

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 description coverage is 100%, so the baseline is 3; both `source` and the rich `v0Compatible` explanation are already fully documented in the schema, and the description adds no additional parameter meaning.

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

Purpose4/5

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

States a specific verb (describe/parse) and resource (Rego policy), then enumerates the returned summary fields (package, imports, rules, clauseCount, isDefault, hasArgs, bodyLength). It is unambiguous what it does, though it does not explicitly contrast itself with near-siblings like rego_parse_ast or rego_inspect.

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?

"Useful as the first step in any 'what does this policy do' workflow" implies a usage context, but there are no explicit when-to-use/when-not conditions or named alternatives among the many sibling analysis tools (rego_inspect, rego_parse_ast, rego_check).

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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