---
layout: default
title: "Capability Vocabulary Technical Specification"
parent: "Tech Specs"
---

# Capability Vocabulary Technical Specification

## Overview

Authorisation in TrustGraph is **capability-based**. Every gateway
endpoint maps to exactly one *capability*; a user's roles each grant
a set of capabilities; an authenticated request is permitted when
the required capability is a member of the union of the caller's
role capability sets.

This document defines the capability vocabulary — the closed list
of capability strings that the gateway recognises — and the
open-source edition's role bundles.

The capability mechanism is shared between open-source and
enterprise editions. The open-source edition ships a fixed
three-role bundle (`reader`, `writer`, `admin`). Enterprise editions
define additional roles by composing their own capability bundles
from the same vocabulary; no protocol, gateway, or backend-service
change is required.

## Motivation

The original IAM spec used hierarchical "minimum role" checks
(`admin` implies `writer` implies `reader`). That shape is simple
but paints the role model into a corner: any enterprise need to
grant a subset of admin abilities (helpdesk that can reset
passwords but not edit flows; analyst who can query but not ingest)
requires a protocol-level change.

A capability vocabulary decouples "what a request needs" from
"what roles a user has" and makes the role table pure data. The
open-source bundles can stay coarse while the enterprise role
table expands without any code movement.

## Design

### Capability string format

`<subsystem>:<verb>` or `<subsystem>` (for capabilities with no
natural read/write split). All lowercase, kebab-case for
multi-word subsystems.

### Capability list

**Data plane**

| Capability | Covers |
|---|---|
| `query` | Read queries: agent, text-completion, prompt, graph-rag, document-rag, embeddings, triples, rows, NLP query, SPARQL, structured-query, mcp-tool |
| `library:read` | List / fetch documents |
| `library:write` | Add / replace / delete documents |
| `collections:read` | List / describe collections |
| `collections:write` | Create / delete collections |
| `knowledge:read` | List / get knowledge cores |
| `knowledge:write` | Create / delete knowledge cores |
| `ingest` | text-load, document-load |
| `export` | Streaming exports (triples, graph-embeddings, document-embeddings, entity-contexts, core-export) |
| `import` | Streaming imports (triples, graph-embeddings, document-embeddings, entity-contexts, rows, core-import) |

**Control plane**

| Capability | Covers |
|---|---|
| `config:read` | Read workspace config |
| `config:write` | Write workspace config |
| `flows:read` | List / describe flows, blueprints, flow classes |
| `flows:write` | Start / stop / update flows |
| `users:read` | List / get users within the workspace |
| `users:write` | Create / update / disable users within the workspace |
| `users:admin` | Assign / remove roles on users within the workspace |
| `keys:self` | Create / revoke / list **own** API keys |
| `keys:admin` | Create / revoke / list **any user's** API keys within the workspace |
| `workspaces:admin` | Create / delete / disable workspaces (system-level) |
| `iam:admin` | JWT signing-key rotation, IAM-level operations |
| `metrics:read` | Prometheus metrics proxy |

### Open-source role bundles

The open-source edition ships three roles:

| Role | Capabilities |
|---|---|
| `reader` | `query`, `library:read`, `collections:read`, `knowledge:read`, `flows:read`, `config:read`, `keys:self` |
| `writer` | everything in `reader` **+** `library:write`, `collections:write`, `knowledge:write`, `ingest`, `export`, `import` |
| `admin` | everything in `writer` **+** `config:write`, `flows:write`, `users:read`, `users:write`, `users:admin`, `keys:admin`, `workspaces:admin`, `iam:admin`, `metrics:read` |

Open-source bundles are deliberately coarse. `workspaces:admin` and
`iam:admin` live inside `admin` without a separate role; a single
`admin` user holds the keys to the whole deployment.

### Authorisation evaluation

For a request bearing a resolved set of roles
`R = {r1, r2, ...}` against an endpoint that requires capability
`c`:

```
allow if c IN union(bundle(r) for r in R)
```

No hierarchy, no precedence, no role-order sensitivity. A user
with a single role is the common case; a user with multiple roles
gets the union of their bundles.

### Unknown capabilities and unknown roles

- An endpoint declaring an unknown capability is a server-side bug
  and fails closed (403, logged).
- A user carrying a role name that is not defined in the role table
  is ignored for authorisation purposes and logged as a warning.
  Behaviour is deterministic: unknown roles contribute zero
  capabilities.

### Capability scope

Every capability is **implicitly scoped to the caller's resolved
workspace**. A `users:write` capability does not permit a user
in workspace `acme` to create users in workspace `beta` — the
workspace-resolver has already narrowed the request to one
workspace before the capability check runs. See the IAM
specification for the workspace-resolver contract.

The three exceptions are the system-level capabilities
`workspaces:admin` and `iam:admin`, which operate across
workspaces by definition, and `metrics:read`, which returns
process-level series not scoped to any workspace.

## Enterprise extensibility

Enterprise editions extend the role table additively:

```
data-analyst:   {query, library:read, collections:read, knowledge:read}
helpdesk:       {users:read, users:write, users:admin, keys:admin}
data-engineer:  writer + {flows:read, config:read}
workspace-owner: admin − {workspaces:admin, iam:admin}
```

None of this requires a protocol change — the wire-protocol
`roles` field on user records is already a set, the gateway's
capability-check is already capability-based, and the capability
vocabulary is closed. Enterprise introduces roles whose bundles
compose the same capabilities differently.

When enterprise introduces a new capability (e.g. for a feature
that does not exist in open source), the capability string is
added to the vocabulary and recognised by the gateway build that
ships that feature.

## References

- [Identity and Access Management Specification](iam.md)
- [Architecture Principles](architecture-principles.md)