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

With no annotations, the description carries the full burden and does reasonably well: it lists the checks run, states SMTP is opt-in and off by default for compliance, and notes the return shape (human summary plus structured data). It still omits rate limits, auth/permission needs, and what enabling SMTP actually risks.

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?

Two tight sentences, front-loaded with the mechanism (DNS-based) and checks, then the key behavioral caveat. 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?

For a 3-param verification tool with full schema coverage and no output schema, the description covers mechanism, checks, the default/compliance behavior and the return format. The main gap is lack of sibling differentiation against verify_bulk, check_mx and is_disposable.

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 schema already documents email, smtp and checks completely, including the smtp compliance note. The description adds nothing beyond that baseline, so a 3 is appropriate.

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+resource ('email verification') and enumerates the concrete checks performed (syntax, MX, disposable, role). It reads clearly as a single-address verifier, but the description itself never differentiates from siblings is_disposable, check_mx and verify_bulk — only the title hints at 'single'.

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 implied (verify an email; SMTP off by default for compliance) but no when-to-use/when-not guidance and no routing to siblings like verify_bulk for batch work or check_mx for MX-only. The compliance caveat on SMTP gives partial practical guidance.

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?

With no annotations, the description must carry the behavioral burden. It usefully discloses that the result is a list sorted by priority, but omits how failures are reported (e.g., NXDOMAIN, no MX records), timeouts, caching, or read-only semantics, so it is only partially transparent.

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?

Two short sentences, purpose front-loaded, return behavior immediately after. No filler, no redundancy, appropriately sized for a simple one-parameter DNS tool.

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?

Given the simple schema and absent output schema, the description should explain return values more fully (e.g., host/preference fields) and at least sketch error behavior. It covers the high-level return concept but leaves those gaps for an agent to guess.

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% and the sole parameter is fully documented in the schema, so the baseline is 3. The description adds no additional semantics about the domain parameter beyond what the schema already states.

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+resource: DNS MX-record lookup, and adds the return shape (sorted mail-exchanger list). However, it does not differentiate from sibling tools like check_email or is_disposable, which is why it falls short of 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?

Usage is only implied: 'Standalone' suggests it needs no other context, and the purpose implies you call it when you need MX records. There is no explicit when-to-use statement, no exclusions, and no routing against the sibling email-verification tools.

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?

With no annotations, the description carries the full disclosure burden. It usefully reveals the data source and freshness (~160k-domain MIT blacklist, auto-refreshed weekly), but omits what a non-match means, how unknowns are treated, and any rate or coverage limits.

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?

Two tight sentences with the capability front-loaded and the accepted input form immediately after. Every clause earns its place and there is no padding.

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 should indicate what the check returns (boolean, matched provider, confidence), but it does not. For a simple one-parameter lookup this is a modest rather than severe 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?

Schema description coverage is 100% and the single parameter already documents 'Email or bare domain' with examples. The description's 'Accepts a full email or a bare domain' restates that rather than adding format, normalization, or subdomain-handling detail, so the baseline 3 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?

States a specific verb and resource ('Detects throwaway / temporary email providers'), which is clearly narrower than siblings like check_mx or verify_bulk. It does not explicitly distinguish itself from check_email, which could plausibly overlap, so it falls short of a 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?

The description says what the tool accepts but never states when to use it versus check_email, verify_bulk, or check_mx. No prerequisites, exclusions, or routing conditions are given, leaving usage entirely to inference.

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?

With no annotations, the description carries the full behavioral burden. It discloses the check type ('Same DNS-based checks as check_email') and the return shape ('per-email array plus a summary'), which is useful, but it omits the SMTP opt-in behavior that the schema documents and says nothing about authentication or rate limits.

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 short sentences with no filler, and the batch scope is front-loaded. It is appropriately sized for a simple bulk verification tool, though it could be slightly tighter by not repeating the 'up to 10 emails' limit already in the title.

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 low-complexity read tool with no output schema and no annotations, the description gives the return format and the nature of the checks. However, it leaves gaps around the smtp option's implications and when to prefer this over single-email verification, so it is adequate rather than complete.

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 schema already documents both the 1–10 email array and the opt-in smtp flag. The description adds no parameter-level detail beyond the batch size already stated in the schema, so the baseline 3 is appropriate.

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: batch verification of up to 10 emails. It also relates itself to the sibling check_email by noting 'Same DNS-based checks,' which helps an agent understand what it does, though it stops short of fully routing between bulk and single-email usage.

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 phrase 'Batch verification of up to 10 emails' implies the tool is for multiple addresses, but there is no explicit when-to-use guidance versus check_email for a single address or versus check_mx/is_disposable. Usage is left to inference from the batch framing.

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