Is a phone number VoIP or a real carrier line? Line type, score and grade, free, no auth.
Scored across 2 tools
The two tools have completely distinct purposes: check_number verifies an individual phone number's line type, while directory returns a provider-level directory. No agent could reasonably confuse them.
check_number follows a clear verb_noun pattern, but directory is a bare noun with no verb prefix. The naming is readable but mixes conventions.
With only two tools, the server feels thin even though both tools serve a coherent read-only purpose. It is on the borderline of being under-scoped.
The server covers its apparent core functions: checking individual numbers and accessing the numberRank directory. It lacks filtering or batch capabilities, but those are reasonable minor gaps for a small read-only utility.
Tells you whether a phone number is VoIP or a real carrier line, with a 0 to 100 score and letter grade, using Twilio Lookup line type intelligence. Use it before relying on a number for SMS or OTP verification. US numbers can be 10 digits; any other country needs + and the country code.
| Name | Required | Description | Default |
|---|---|---|---|
| number | Yes | Phone number, for example +15551234567 |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, covering the safety profile. The description adds useful behavior beyond that: it explains the output format (score and grade) and input formatting rules (US 10 digits, others require + and country code). This enriches the agent's understanding without contradicting annotations.
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 three sentences, each earning its place: the first explains the core function, the second gives a use case, and the third details input formatting. It is front-loaded with the most critical information and contains no filler or repetition.
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?
For a simple read-only lookup with one parameter and no output schema, the description covers all essentials: purpose, usage context, input format, and output type. Annotations handle safety. Nothing an agent needs to call the tool correctly is missing.
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?
Schema description coverage is 100%, so the baseline is 3. The description adds meaningful parameter semantics by specifying formatting requirements: US numbers can be 10 digits, while other countries need + and the country code. This goes beyond the schema's example and helps the agent construct valid inputs.
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 states a specific verb and resource: it tells whether a number is VoIP or a carrier line, with a 0-100 score and letter grade, using Twilio Lookup. This clearly distinguishes it from the sibling tool 'directory', whose name suggests a different purpose. No ambiguity about what the tool does.
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 gives a concrete use case: 'Use it before relying on a number for SMS or OTP verification.' It does not mention alternatives or exclusions, but the single sibling 'directory' is unrelated, so no competitive guidance is needed. This provides clear context for when to invoke the tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Returns the numberRank directory: AI agent phone providers and personal agents graded by whether their published and provisioned numbers read as real carrier lines or VoIP. Numbers are masked.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotations already establish read-only, idempotent, and non-destructive behavior, so the description only needs to add context beyond those hints. It discloses that numbers are masked and that grading is based on published and provisioned numbers, which is genuinely useful privacy-relevant behavior.
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 a single sentence that front-loads the return action and keeps the core content brief. The 'numberRank' phrase is slightly cryptic, but the sentence has no wasted clauses and the masking note earns its place.
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?
For a zero-parameter, read-only listing tool, the description covers what is returned and a key output behavior, and the annotations cover safety and idempotence. It does not mention ordering or pagination, but those are minor gaps given the tool's simplicity and absence of an output schema.
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 tool takes no parameters, so there are no parameter semantics for the description to clarify. For a zero-parameter tool the baseline is 4, and the description adds no conflicting or confusing parameter information.
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 uses a specific verb ('Returns') and names a concrete resource: a directory of AI agent phone providers and personal agents graded by line type. It is clearly a listing tool rather than the check_number sibling, though the unexplained 'numberRank' brand term and lack of explicit contrast keep it from a perfect 5.
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?
There is no guidance about when to use this listing tool versus check_number or any other alternative. The directory-style wording implies it is meant for broad lookups, but an agent has to infer that usage boundary rather than being told.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
check_numberdirectoryRead-only phone intelligence for AI voice agents — line type, risk, DNC, signed receipts.
Phone carrier lookup, append, verification, DNC, and fraud data services.
Is this number safe to call or text right now? Live carrier, CNAM, spam and SMS checks for agents.
Preview a TCPA/GDPR/CASL/10DLC gate result before spending a paid send. No key needed.
Add one secure layer between your agents and this server.
