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Rego test coverage gaps

rego_coverage_gaps

Find Rego test coverage gaps by running OPA tests and reporting uncovered line ranges per file, ordered from lowest to highest coverage so weak spots surface first.

Instructions

Run opa test --coverage and return a per-file breakdown of uncovered line ranges. Identifies which rules or branches are not yet exercised by tests. Files are sorted by coverage ascending so the worst-covered files appear first. Use threshold to limit the report to files below a target coverage percentage.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
pathsYesTest directories or files. opa test looks for *_test.rego siblings of source files.
thresholdNoReport only files below this coverage percentage (0-100). When omitted, all files with uncovered ranges are reported.
runPatternNoRun only tests whose names match this regex.
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
    • changedInput schema / properties / v0Compatible / description
      Previous value: -"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."New value: +"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."
  2. Changed1 schema field changedv0.7.0
    • 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.",
+  "type": "boolean"
+}
  3. Addedv0.1.13

TDQS

A3.5/5.0
Behavior3/5

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

Annotations declare readOnlyHint=false and openWorldHint=true, so the safety profile is at least partly covered. The description adds useful behavioral detail (per-file breakdown, ascending sort order) but says nothing about cost, side effects of executing test code, or prerequisite test files, which matters given readOnlyHint=false.

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?

Four tight sentences, front-loaded with the core action and outcome, then sort behavior and the threshold hint. No filler or redundancy, though the last sentence slightly duplicates the schema's threshold text.

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 does its job by characterizing the return value (per-file uncovered line ranges, sorted worst-first). It omits what happens when no tests exist or when paths contain no matching *_test.rego files, but it is otherwise sufficient for correct invocation.

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 schema already documents all four parameters, including threshold and v0Compatible. The description restates threshold semantics and the sort behavior but adds no format, syntax, or edge-case detail beyond what the schema provides. Baseline 3 applies.

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 and resource: runs `opa test --coverage` and returns per-file uncovered line ranges, identifying unexercised rules/branches. Clear to an agent. However, it never distinguishes itself from close siblings like rego_test or rego_eval_with_coverage, leaving differentiation implicit.

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 only usage guidance is 'Use threshold to limit the report to files below a target coverage percentage', which is parameter mechanics rather than when-to-use. There is no statement of when to pick this over rego_test, rego_test_multiroot, or rego_eval_with_coverage, so selection is left to inference.

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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