chembl-mcp-server

chembl-dataframe-describe

chembl_dataframe_describe

Read-onlyIdempotent

List the tables and columns staged on a canvas by chembl_get_bioactivities — inspect before calling chembl_dataframe_query to write correct SQL. Returns each table with its row count, kind (table | view), and column names + types. Unavailable when the server sets CANVAS_PROVIDER_TYPE=none.

Input Schema

Name	Required	Description	Default
`canvas_id`	Yes	Canvas ID returned by chembl_get_bioactivities — non-null whenever that call staged a table.

Output Schema

Name	Required	Description	Default
`error`	No	Present when the call failed. Absent on success.
`tables`	No	Tables and views staged on the canvas.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 24, 2026

changedOutput schema / properties / error / properties / data / properties / reason / description

Previous value: -"Machine-readable failure mode. Declared by this tool: `canvas_disabled`: Called while CANVAS_PROVIDER_TYPE is not duckdb, so no canvas exists. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `canvas_disabled`: The server runs with the canvas off (CANVAS_PROVIDER_TYPE=none), so no canvas exists. Other values are possible when a failure originates below the handler."

Changed1 schema field changedOct 18, 2026

changedInput schema / properties / canvas_id / description

Previous value: -"Canvas ID returned by chembl_get_bioactivities (spilled: true)."New value: +"Canvas ID returned by chembl_get_bioactivities — non-null whenever that call staged a table."

Changed1 schema field changedSep 19, 2026
- addedInput schema / properties / canvas_id / pattern
```
Added value: +"^[A-Za-z0-9_-]{10}$"
```

Changed6 schema fields changedAug 25, 2026

changedInput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedInput schema / additionalProperties
```
Added value: +false
```

changedOutput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedOutput schema / anyOf

Added value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "tables"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]

addedOutput schema / properties / error

Added value: +{
+  "additionalProperties": {},
+  "description": "Present when the call failed. Absent on success.",
+  "properties": {
+    "code": {
+      "description": "JSON-RPC error code for this failure.",
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "data": {
+      "additionalProperties": {},
+      "properties": {
+        "reason": {
+          "description": "Machine-readable failure mode. Declared by this tool: `canvas_disabled`: Called while CANVAS_PROVIDER_TYPE is not duckdb, so no canvas exists. Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "canvas_disabled"
+          ],
+          "type": "string"
+        },
+        "recovery": {
+          "additionalProperties": {},
+          "description": "Actionable next step for the caller.",
+          "properties": {
+            "hint": {
+              "type": "string"
+            }
+          },
+          "required": [
+            "hint"
+          ],
+          "type": "object"
+        },
+        "retryable": {
+          "description": "Whether retrying may succeed.",
+          "type": "boolean"
+        }
+      },
+      "type": "object"
+    },
+    "message": {
+      "description": "Human-readable description of what went wrong.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "code",
+    "message"
+  ],
+  "type": "object"
+}

removedOutput schema / required
```
Removed value: -[
-  "tables"
-]
```

First observedAug 13, 2026

TDQS

A4.7/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent and closed-world, and the description adds the operationally important availability gate (server-side CANVAS_PROVIDER_TYPE=none). It also characterizes the result shape (row count, kind table|view, column names + types), though that partially duplicates the output schema. It does not mention empty-canvas behavior, which is a minor remaining gap.

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?

Three short sentences, front-loaded with the core action, then the routing advice, then the availability caveat. No filler or restatement of the title.

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?

With an output schema present, return values need not be explained, and one fully-described required parameter plus explicit annotations leave little unsaid. The availability limitation and the prerequisite relationship to chembl_get_bioactivities are both covered.

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% and the schema already documents canvas_id's origin and format, so the baseline is 3. The description adds a small amount by framing the parameter's lifecycle — the canvas is staged by chembl_get_bioactivities — which reinforces the call-order dependency for the agent.

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?

Specific verb + resource: lists tables and columns staged on a canvas, and attributes them to the sibling that created them (chembl_get_bioactivities). It also names the counterpart tool (chembl_dataframe_query), so an agent can separate inspection from querying without opening a schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit sequencing: "inspect before calling chembl_dataframe_query to write correct SQL" gives both the alternative and the condition that selects this tool. It additionally states an exclusion — unavailable when CANVAS_PROVIDER_TYPE=none — which no other field conveys.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All chembl-mcp-server tools Inspect

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