PayPerFax

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

Annotations only say readOnlyHint=false and destructiveHint=false; the description goes well beyond that. It discloses the full two-step flow (prepare → person pays in browser → fax sent), that nothing is sent or charged before payment, that confirmation arrives only after payment, and that a "failed" status means no charge and a possible retry. This is rich behavioral context an agent could not infer from the 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 opening paragraph is well front-loaded and the seven numbered rules are scannable and each carries distinct content. It is on the long side and some sentences read as workflow coaching rather than tool specification, but for a 12-parameter tool with a multi-step human-in-the-loop flow the length is largely earned.

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?

There is no output schema, so the description must carry return-value disclosure, and it does: the tool returns a link for the person, and the fax outcome surfaces later via status. Combined with the payment/charge/failure semantics, an agent has everything needed to invoke the tool and set expectations for the person.

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, but the description adds real semantics the schema lacks: the 100 KB markdown limit, that cover_message is truncated if long, that file_expected drives a form where the person uploads the file, and the email requirement for markdown/cover-page sends. It adds cross-parameter interaction guidance rather than restating field docs.

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+resource ("Prepare a fax") and immediately scopes it: the tool does not send and does not charge, it returns a link. That framing cleanly separates it from the siblings get_fax_status (checking) and list_supported_formats (formats). An agent can tell what this tool does and does not do without opening the 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?

Rules 1-6 give explicit when-to-use guidance: ask for email, do not retype a file the person already has (set file_expected), source the fax number from an official site, use markdown for letters you author. Rule 6 names a concrete alternative path (direct curl HTTP call for local files), which is exactly the alternative-routing the dimension rewards.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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

Annotations only declare readOnlyHint=true, so the description carries the real load: it enumerates the status state machine (pending/delivered/failed/expired), expands the pending sub-stages, and discloses billing and recovery behavior (not charged on failure, can resend, render_failed requires the person to reopen the link). That is behavior an agent cannot get from the annotation.

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 critical instruction and the accepted identifier forms are front-loaded, and the state definitions are dense but each earns its place. The parentheticals make it slightly longer than needed, but there is no filler.

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?

There is no output schema, yet the description documents the returned fields (status, stage, pages, price) and their meanings, which is exactly what the agent needs to interpret the response. Nothing material is missing for a single-parameter read tool.

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% for the single id parameter, so the baseline is 3. The description restates the id-or-address duality and adds the 'status address from the tracking prompt' phrasing, but adds little semantic weight beyond the schema.

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 opening sentence 'Read where a fax is' gives a specific verb (read) and resource (fax status), and the surrounding detail about id vs. address forms makes the scope unambiguous. It is clearly distinguishable from siblings create_fax and list_supported_formats.

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 trigger condition ('read the status when the person asks') and an explicit when-not ('Do not call this in a loop'), and points to create_fax as the source of the id. It stops short of naming an alternative tool for status reads, but no such sibling exists.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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

Annotations already declare readOnlyHint=true, so the safe read profile is covered. The description adds that the result is a catalog of accepted inputs and limits, but does not describe the response shape, pagination, or whether the list is static.

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?

A single front-loaded sentence that leads with the action ('List what PayPerFax can fax') and then enumerates the covered dimensions. No filler or 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?

There is no output schema, but the description effectively previews the return contents (text, file types, sizes, languages), which covers what an agent needs to know. A brief note on when to invoke it would close the remaining gap.

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 zero parameters, so the baseline is 4. There is no parameter surface to disambiguate and the description correctly implies no inputs are required.

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?

States a specific verb ('List') and resource (supported fax formats), and enumerates the dimensions covered: text input, file types, sizes, and languages. It also loosely distinguishes itself by referencing create_fax's inputs and the HTTP call path, which helps separate it from the sibling tools.

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 is only implied: a reader can infer this is a reference/discovery call to make before create_fax, but the description never says 'call this first' or when not to bother. No explicit alternative or exclusion is given.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.