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Discover protocol features + limits

demand.capabilities

Read-only

Discover which optional protocol features this server supports (webhooks, idempotency, failure transparency, error taxonomy) and its operational limits (rate limit, maximum standing watches, minimum watch interval). Call once when you connect and adapt to the answer - skip webhook setup if 'webhooks' is absent, and respect the limits rather than discovering them by being throttled. Free, instant, no side effects. Protocol v1.1 §8.2.

Input Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Output Schema

TableJSON Schema

Name	Required	Description
`limits`	No	Operational limits to respect.
`features`	No	Optional features supported, e.g. webhooks, idempotency, failure_transparency, error_taxonomy.
`protocol_version`	Yes	Demand-protocol version.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 25, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "properties": {
+    "features": {
+      "description": "Optional features supported, e.g. webhooks, idempotency, failure_transparency, error_taxonomy.",
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "limits": {
+      "additionalProperties": true,
+      "description": "Operational limits to respect.",
+      "properties": {
+        "max_watches": {
+          "description": "Standing watches one caller may hold.",
+          "type": [
+            "integer",
+            "null"
+          ]
+        },
+        "min_check_interval_seconds": {
+          "description": "Floor on how often a watch re-runs.",
+          "type": [
+            "integer",
+            "null"
+          ]
+        },
+        "rate_limit_per_minute": {
+          "description": "Calls per minute before throttling.",
+          "type": [
+            "integer",
+            "null"
+          ]
+        }
+      },
+      "type": "object"
+    },
+    "protocol_version": {
+      "description": "Demand-protocol version.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "protocol_version"
+  ],
+  "type": "object"
+}

AddedJun 8, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true and destructiveHint=false; the description reinforces this with 'Free, instant, no side effects' and adds practical behavioral guidance like 'call once' and adapting based on the answer. It goes beyond the annotations by describing performance and idempotent usage, without contradicting them.

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 sentences with no redundancy. It leads with purpose, immediately gives actionable usage guidance, and closes with a protocol reference. Every sentence earns its place.

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 the presence of an output schema (which will define the return structure), the description covers why to call, when to call, and how to use the result. It also notes the tool is side-effect-free, which is sufficient for a capabilities discovery endpoint.

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?

There are zero parameters, and the schema is an empty object, so schema coverage is effectively 100%. The description adds no parameter details because none exist; the baseline of 4 is appropriate since there is nothing to clarify.

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 states a clear verb ('Discover') and a specific resource ('optional protocol features... and its operational limits'), listing concrete examples (webhooks, idempotency, rate limit, etc.). It is distinct from sibling tools like demand.health or demand.list_constraints, which focus on status or constraints, not feature discovery.

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?

Explicitly says 'Call once when you connect' and instructs how to adapt: skip webhook setup if 'webhooks' is absent, and respect limits to avoid throttling. While it doesn't name alternative tools, the context makes it clear this is the initial discovery call. Slight deduction for not explicitly contrasting with siblings.

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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