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opa-mcp-server

by OrygnsCode
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Verify OPA bundle signature

opa_bundle_verify
Read-onlyIdempotent

Verify a signed OPA bundle's signature against a public key to confirm authenticity and detect any modified, added, or missing files.

Instructions

Verify the signature of a signed bundle directory or .tar.gz archive with the public key. OPA has no standalone verify command, so this runs opa build --verification-key into a private temp file that is discarded. A directory is verified by name from its parent, matching how opa_bundle_sign signs it. OPA reads the key, checks the JWT in .signatures.json, compares the scope claim, then checks every file: Rego files by digest before parsing, data files and .manifest by parsed value, so an unparseable data file fails before its digest is compared. Failures return INVALID_BUNDLE with details.reason set to one of signature_invalid, scope_mismatch, file_modified, file_added, file_missing, file_unparseable, unsigned, signatures_malformed, not_a_bundle, bundle_load_error, or unknown when the message is not recognised; the raw output is in details. A key or algorithm OPA cannot use returns INVALID_INPUT. Pass scope exactly as the bundle was signed with. With a single key OPA does not check verificationKeyId against the signature keyid claim. verified: true is returned only when OPA loaded the bundle with its signature intact.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
scopeNoExpected `scope` claim in the signature. Pass exactly the value the bundle was signed with, and nothing if it was signed without one; the failure reason is scope_mismatch otherwise.
bundleYesPath to the signed bundle directory or `.tar.gz` archive. Must be inside an allowed root.
signingAlgNoSigning algorithm used when the bundle was signed (e.g. `RS256`, `PS256`, `ES256`, `HS256`). Defaults to `RS256`.
v0CompatibleNoLoad the bundle as Rego v0 (`--v0-compatible`). A policy written before Rego v1 otherwise fails to load, after the signature and digests have already been checked.
verificationKeyYesPath to the PEM file containing the RSA or ECDSA public key, or for HMAC algorithms a file holding the secret. Must be inside an allowed root.
verificationKeyIdNoName the key is registered under for OPA (`--verification-key-id`, default `default`). With a single key OPA verifies against it regardless of the signature keyid claim, so this rarely needs setting.

Schema Changelog

Changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. Changed4 schema fields changedv0.5.0
    • changedInput schema / properties / scope / description
      Previous value: -"Expected `scope` value in the bundle signature. Required when the bundle was signed with `--scope`."New value: +"Expected `scope` claim in the signature. Pass exactly the value the bundle was signed with, and nothing if it was signed without one; the failure reason is scope_mismatch otherwise."
    • addedInput schema / properties / v0Compatible
      Added value: +{
+  "description": "Load the bundle as Rego v0 (`--v0-compatible`). A policy written before Rego v1 otherwise fails to load, after the signature and digests have already been checked.",
+  "type": "boolean"
+}
    • changedInput schema / properties / verificationKey / description
      Previous value: -"Path to the PEM file containing the RSA or ECDSA public key, or the path to the HMAC secret file. Must be inside an allowed root."New value: +"Path to the PEM file containing the RSA or ECDSA public key, or for HMAC algorithms a file holding the secret. Must be inside an allowed root."
    • changedInput schema / properties / verificationKeyId / description
      Previous value: -"Key ID that must match the `keyid` field in the bundle signature. Required when the bundle was signed with `--public-key-id`."New value: +"Name the key is registered under for OPA (`--verification-key-id`, default `default`). With a single key OPA verifies against it regardless of the signature keyid claim, so this rarely needs setting."
  2. Addedv0.1.13

TDQS

A4.6/5.0
Behavior5/5

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

Annotations already indicate read-only, idempotent, non-destructive behavior, and the description goes well beyond that by disclosing the temp-file mechanism, the file-by-file verification order, digest-vs-parsed-value differences, failure reason enumerations, and the precise condition for returning `verified: true`. It also surfaces the `verificationKeyId` nuance.

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?

The description is long but every sentence carries substantive behavioral or edge-case information for a complex tool. It is front-loaded with the core purpose and implementation, then proceeds into verification details and error conditions. Some schema repetition exists, such as the `scope` instruction, but overall it earns its length.

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

Completeness5/5

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

Given there is no output schema, the description thoroughly documents return behavior: `INVALID_BUNDLE` with an enumerated `details.reason`, `INVALID_INPUT` for unusable keys or algorithms, and the exclusive condition for `verified: true`. It also covers failure ordering, v0 compatibility, directory verification convention, and key-ID behavior, making the tool self-sufficient for correct invocation.

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?

Schema coverage is 100%, so a baseline of 3 applies, but the description adds meaningful semantics: `scope` is emphasized as needing to match the signing value exactly, `v0Compatible` is tied to post-signature failure behavior, and `verificationKeyId` is explained as rarely needing to be set with a single key. This enriches the schema without being redundant.

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 opening sentence names a specific verb and resource: 'Verify the signature of a signed bundle directory or `.tar.gz` archive with the public key.' It also clarifies the implementation mechanism and the matching relationship to `opa_bundle_sign`, which distinguishes it from general Rego verification siblings like `rego_verify` and `conftest_verify`.

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 gives strong usage context: it explains that OPA has no standalone verify command, how the verification is performed, what inputs are required, and how `scope` must exactly match the signing value. It does not explicitly name alternative tools or say when not to use this tool, but the guidance is clear enough to invoke correctly.

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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