Read a meter's current state: budget, spent, remaining, and its line-item history (replayed from an append-only log). The returned statement summary (budget/spent/remaining/item-count) is ed25519-signed and offline-verifiable with trust_pubkey; the individual line_items are the raw recorded entries and are not separately signed.
| Name | Required | Description | Default |
|---|---|---|---|
| meter_id | Yes | The meter_id from meter_open |
Changes observed during successful MCP inspections.
Input schema / $schemaPrevious value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description discloses key behavioral traits: it returns a signed statement (ed25519) and raw line items, explains verification with trust_pubkey, and notes that line items are not separately signed. This complements the readOnlyHint annotation by adding cryptographic detail without contradiction.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is two sentences, front-loaded with the core action and followed by essential details on verification. Every sentence adds value without redundancy.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Despite lacking an output schema, the description thoroughly explains the return structure (statement with budget/spent/remaining/item-count, line items) and verification. With a single parameter and no nested objects, this is complete for an agent to understand the tool's behavior.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The input schema has 100% coverage with a clear description for meter_id. The tool description does not add extra parameter semantics beyond the schema; it focuses on output. A baseline of 3 is appropriate given high schema coverage.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool reads a meter's current state, including budget, spent, remaining, and line-item history. It distinguishes itself from sibling tools like meter_open and meter_charge by specifying the read-only nature and the signed statement feature. The verb 'Read' and resource 'meter' are specific.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies use for checking meter state but lacks explicit when-not-to-use guidance or alternatives. However, the read-only annotation (readOnlyHint) hints at non-mutating use, and the sibling context provides implicit differentiation. A slight gap remains in directing agents away from this tool for write operations.
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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