check_balanceGet the prepaid credit balance of the API key used to authenticate this MCP connection. Requires a bearer API key (stf_live_...). Buy or top up credits at https://www.sendthisfax.com/en/credits — credits never expire and failed faxes are re-credited automatically.
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Adds value beyond annotations by noting authentication type, credit expiration policy, and refund behavior. No contradictions with readOnlyHint.
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?
Three efficient sentences: purpose, requirement, policy. Front-loaded and no wasted words.
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?
Fully adequate for a zero-parameter read-only tool; covers authentication and credit policy.
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?
With zero parameters and 100% schema coverage, baseline is 4. Description does not need to add parameter info.
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?
Clearly states the verb 'Get' and the specific resource 'prepaid credit balance of the API key'. Distinguishes from siblings which are for status, price, and fax sending.
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?
Provides clear context on authentication requirement and where to buy credits, but does not explicitly contrast with sibling tools or state when not to use.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.
Each tool has a clearly distinct purpose: checking balance, getting fax status, pricing, and sending. No overlap.
All tool names follow a consistent verb_noun pattern: check_balance, get_fax_status, get_price, send_fax.
Four tools is appropriate for a focused fax service, covering the essential operations without unnecessary clutter.
Core workflow (price, send, status, balance) is covered. Missing cancellation or listing tools, but these are not essential for the primary use case.