Blockstream Info

Mempool

mempool

Read-onlyIdempotent

Mempool size + fee histogram.

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "network": "mainnet"
    },
    "name": "mempool"
  }
}

Input Schema

Name	Required	Description	Default
`network`	No

Output Schema

Name	Required	Description
`count`	No	Transaction count in mempool
`vsize`	No	Total virtual size
`total_fee`	No	Total fees in satoshis
`fee_histogram`	No	Fee histogram [fee_rate, vsize]

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedMay 27, 2026

addedInput schema / examples

Added value: +[
+  {
+    "network": "mainnet"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "count": {
+      "description": "Transaction count in mempool",
+      "type": "number"
+    },
+    "fee_histogram": {
+      "description": "Fee histogram [fee_rate, vsize]",
+      "items": {
+        "items": {
+          "type": "number"
+        },
+        "type": "array"
+      },
+      "type": "array"
+    },
+    "total_fee": {
+      "description": "Total fees in satoshis",
+      "type": "number"
+    },
+    "vsize": {
+      "description": "Total virtual size",
+      "type": "number"
+    }
+  },
+  "type": "object"
+}

First observedMay 13, 2026

TDQS

C2.9/5.0

Behavior2/5

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the description adds no behavioral details. It does not mention data freshness, rate limits, or what exactly 'mempool size' and 'fee histogram' entail.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is extremely short at 4 words, which is concise but under-specified. It lacks crucial detail about the output format and parameter usage, making it minimally adequate.

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?

Given the tool's simplicity (one parameter, output schema exists), the description still omits essential context like what 'mempool size' refers to (e.g., number of transactions, bytes) and how the histogram is structured. This leaves the agent with gaps in understanding.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The single parameter 'network' has 0% schema description coverage, and the description does not mention it at all. The agent gets no guidance on valid values or its effect. With low coverage, the description must compensate but fails to do so.

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 clearly states the tool returns 'mempool size + fee histogram', which is a specific verb (retrieve) and resource (mempool data). This distinguishes it from siblings like 'fee_estimates' and 'tip_height', which serve different purposes.

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

Usage Guidelines2/5

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

No guidance is provided on when to use this tool versus alternatives, or any context regarding prerequisites or exclusions. The user must infer intent from the name alone.

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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