Look up verified US government fax numbers and send a fax from the chat. Two tools: lookup_fax_number searches 1,200+ numbers (SSA field offices, state unemployment and Medicaid agencies, IRS by form, FEMA), each with its official source page and last-verified date; send_fax opens a send form in the chat. No account, $2.99 per fax charged only on delivery. Send-only. English and Spanish.
Scored across 2 tools
The two tools have clearly distinct purposes: one looks up a fax number, the other sends a fax. There is no overlap in action or resource, so an agent can easily select the right tool.
Both names use consistent snake_case with a clear verb_noun pattern: lookup_fax_number and send_fax. The slight difference in noun length does not break the convention.
The server is very narrowly scoped, and the two tools cover its core actions. However, two tools is thin for a faxing service and leaves little room for supporting operations such as delivery status or cancellation.
The surface covers number lookup and sending, but lookup is explicitly limited to a fixed list of agencies and there is no tool to check delivery status, cancel a fax, or review history. These are notable gaps for a fax workflow, though the core send path is present.
Find the fax number for a US state or federal agency, with the official source it was read from and when it was last verified. Covers Social Security field offices across 56 states and territories (search by city or state), MassHealth, California EDD, Illinois IDES, NJ FamilyCare, IRS Form 2553, FEMA, the state unemployment agencies of Alabama, Colorado, Indiana, Iowa, Kentucky, Maryland, Missouri, New Jersey, New York, South Carolina, Texas, Wisconsin, and the state Medicaid agencies of Florida, Georgia, Idaho, Louisiana, Montana, Nebraska, New Mexico, Oregon, Texas, Utah, Washington. It has no numbers for any other agency. Social Security and Medicaid publish no national fax number, so a lookup for either needs a city or a state. Returns nothing rather than guessing when it has no verified number for an agency.
| Name | Required | Description | Default |
|---|---|---|---|
| city | No | City or town, used to pick a Social Security field office. Optional. | |
| state | No | Two-letter US state code, for example TX. Optional, and the only place a bare code is read. | |
| agency | Yes | The agency to look up, in the user's own words, for example "MassHealth", "Texas Workforce Commission" or "social security office in Denver". | |
| language | No | Language for the response. Defaults to English. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, idempotent, closed-world, non-destructive), and the description still adds real behavior: results carry the official source and last-verified date, and the tool fails closed by returning nothing rather than guessing. Missing only operational notes such as latency or whether a fuzzy agency string can return multiple candidates.
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 purpose and the city/state constraint are front-loaded, but the long roll-call of covered states and agencies consumes substantial text for scope that could be summarized more compactly. Every clause is informative, yet the enumeration is token-heavy relative to the decision it supports.
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?
With no output schema, the description compensates by describing what comes back (number, source, verification date) and the empty-result behavior, which is what an agent needs before calling. Given the closed-world read tool, only a note on ambiguous agency matches is arguably 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 coverage is 100%, so the baseline is 3, and the description earns above that by explaining that agency is matched from the user's own words and that city/state are the disambiguators required for SSA and Medicaid. It adds the rule that state is the only field read as a bare code, which the schema only hints at.
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?
"Find the fax number for a US state or federal agency" is a specific verb+resource, and the enumerated coverage (SSA field offices, MassHealth, state UI/Medicaid agencies) makes the scope unmistakable. It never names the sibling send_fax, so the lookup-versus-send distinction is left to be inferred from the verb.
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?
It states the applicability conditions clearly, including the negative boundary "It has no numbers for any other agency" and the rule that SSA and Medicaid lookups require a city or state. It does not tell the agent when to route to send_fax instead, or what to do after a miss beyond the fact that nothing is returned.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Start a fax to a US fax number. Opens a form in this chat where the user adds pages from their phone camera or a PDF, adds an optional cover page, and pays. The fax costs $2.99 flat for up to 25 pages and is charged only when delivery is confirmed. No account is needed. Nothing is sent or charged until the user confirms and pays in that form. A file attached to this chat cannot be passed to this tool, so the user adds the document inside the form, and a document already attached does not need to be uploaded to the chat again. On a host that cannot show the form, this returns a link that opens the same flow in a browser.
| Name | Required | Description | Default |
|---|---|---|---|
| agency | No | The agency the fax is going to, if known. Used for reporting only. | |
| language | No | Language for the response. Defaults to English. | |
| fax_number | No | The destination US fax number, in any format, including as printed on a letter or form the user attached. |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only give the generic non-read-only/open-world profile; the description adds the material behavior: nothing is sent or charged until the user confirms and pays in the form, and billing happens only on confirmed delivery. It also discloses the host-dependent fallback (returns a link) and the constraint that chat attachments cannot be passed in — exactly the surprises an agent would otherwise hit.
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?
Front-loaded with purpose and mechanism, then cost, then the attachment caveat and fallback — a logical order with no filler. It runs slightly long at six sentences, and the two attachment sentences could be merged, but nothing is redundant.
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 form-driven, human-in-the-loop tool with no output schema, the description covers everything needed to set expectations: where the document goes, what the user pays, when charging occurs, and what happens on hosts without form support.
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 each of agency, language, and fax_number is already documented, including that the number may come from an attached letter. The description adds no parameter-level meaning beyond the schema's own note, so the baseline applies.
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 opens with a concrete verb and resource — "Start a fax to a US fax number" — and immediately clarifies the interaction model (a form opens in the chat). That is enough to distinguish it from the only sibling, lookup_fax_number, without reading either schema.
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?
Usage context is explicit: no account needed, US numbers only, $2.99 flat up to 25 pages, and a browser-link fallback for hosts that cannot render the form. The one gap is that it never tells the agent to call lookup_fax_number first when the destination number is unknown, which is the obvious companion action.
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.
lookup_fax_numbersend_fax
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