Subo

Add a block

add_block

Append one block to a project's script. Read the subo://guide/authoring resource before writing blocks: block type names, section names and the piping rules are not guessable.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "project_id": "<project_id>",
      "type": "<type>",
      "prompt": "<prompt>"
    },
    "name": "add_block"
  }
}

Input Schema

Name	Required	Description
`max`	No
`min`	No
`name`	No
`type`	Yes
`color`	No
`scale`	No
`prompt`	Yes
`upload`	No
`options`	No
`section`	No
`position`	No
`required`	No
`continue_`	No
`hide_when`	No
`image_url`	No
`show_when`	No
`project_id`	Yes	Project id, from list_projects or create_project.
`rank_top_n`	No
`action_kind`	No
`answer_style`	No
`precondition`	No
`when_correct`	No
`action_config`	No
`text_analysis`	No
`thumbnail_url`	No
`when_incorrect`	No
`randomize_options`	No
`calculated_formula`	No
`correct_answer_ids`	No
`correct_answer_index`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedNov 10, 2026

addedInput schema / $defs / UploadSchema

Added value: +{
+  "description": "A `file_upload` block's rules. Every field is optional: images and documents,\none file, required, up to the community's plan limit.",
+  "properties": {
+    "categories": {
+      "anyOf": [
+        {
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "default": null,
+      "title": "Categories"
+    },
+    "max_bytes": {
+      "anyOf": [
+        {
+          "type": "integer"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "default": null,
+      "title": "Max Bytes"
+    },
+    "max_files": {
+      "anyOf": [
+        {
+          "type": "integer"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "default": null,
+      "title": "Max Files"
+    },
+    "min_files": {
+      "anyOf": [
+        {
+          "type": "integer"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "default": null,
+      "title": "Min Files"
+    }
+  },
+  "title": "UploadSchema",
+  "type": "object"
+}

addedInput schema / properties / upload

Added value: +{
+  "anyOf": [
+    {
+      "$ref": "#/$defs/UploadSchema"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null
+}

Changed4 schema fields changedOct 15, 2026

changedInput schema / $defs / ActionConfigSchema / properties / fire_scope / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "enum": [
+      "respondent",
+      "session"
+    ],
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / $defs / BlockOptionSchema / properties / anchor_position / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "const": "last",
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / $defs / ContinueSchema / properties / after / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "enum": [
+      "pause",
+      "click"
+    ],
+    "type": "string"
+  },
+  {
+    "type": "null"
+  }
+]

changedInput schema / $defs / ContinueSchema / properties / pause / anyOf

Previous value: -[
-  {
-    "type": "integer"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "minimum": 0,
+    "type": "integer"
+  },
+  {
+    "type": "null"
+  }
+]

Changed1 schema field changedOct 6, 2026

addedInput schema / properties / text_analysis

Added value: +{
+  "anyOf": [
+    {
+      "type": "boolean"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "title": "Text Analysis"
+}

First observedOct 5, 2026

TDQS

A3.5/5.0

Behavior3/5

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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=false, so safety and repeat-call behavior are partly covered. The description adds that the operation appends to an existing script, but says nothing about validation failure modes, position/ordering behavior, or whether a retry creates a duplicate block — a notable gap for a 30-param mutation tool.

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?

Two short sentences, zero filler, and the mutation action leads while the prerequisite follows. Nothing could be cut without losing information.

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

Completeness2/5

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

For a high-complexity mutation tool (30 params, conditional schemas, 3% schema coverage, no output schema), the description supplies almost no parameter-level or return-value information. The external-resource pointer is valuable but assumes the agent can read it, leaving the definition itself inadequate on its own.

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 description coverage is 3% out of 30 parameters, so the description bears nearly the full burden. Rather than explaining parameters, it does the next best thing: it points to the authoritative authoring resource and flags the specific classes of values that cannot be guessed (block type names, section names, piping rules). The nested $defs schemas do explain structural semantics once an agent gets there. It remains weak on the many optional fields, so it does not fully compensate for the coverage gap.

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 ("Append one block to a project's script"), which distinguishes it from update_block and delete_block by the append/one-block scoping. It stops short of explicitly naming those siblings, but the action is unambiguous.

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?

Gives a clear prerequisite (read subo://guide/authoring before writing blocks) with a stated reason: type names, section names and piping rules are not guessable. It does not say when to prefer update_block/delete_block or what conditions make this the wrong tool, so guidance is implied rather than explicit.

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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