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by me.drwho
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CORS checker

dossier_cors
Read-only

Send a CORS preflight (OPTIONS) to https:/// and return the access-control-* headers in the answer. Use to check whether a site accepts cross-origin requests from a given origin and method. One request, 5 s timeout. Returns JSON with a status field: {status:"ok", data, fetchedAt} on success, {status:"not_applicable", reason} when the thing is genuinely absent, {status:"timeout", ms}, or {status:"error", message} when it could not be determined. Treat not_applicable as a finding and error as unknown.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
domainYesPublic domain name, e.g. example.com. IP addresses, ports, paths and protocol prefixes are rejected.
methodNoAccess-Control-Request-Method to send, e.g. POST. Defaults to GET.
originNoOrigin header to send, e.g. https://app.example.com. Defaults to https://domainposture.com.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed4 schema fields changed
    • removedInput schema / additionalProperties
      Removed value: -false
    • changedInput schema / properties / domain / description
      Previous value: -"Public FQDN, e.g. example.com. Must be resolvable on the public internet; IPs, ports, paths, and protocol prefixes are rejected."New value: +"Public domain name, e.g. example.com. IP addresses, ports, paths and protocol prefixes are rejected."
    • changedInput schema / properties / method / description
      Previous value: -"Access-Control-Request-Method header value, e.g. POST or PUT. Defaults to GET if omitted."New value: +"Access-Control-Request-Method to send, e.g. POST. Defaults to GET."
    • changedInput schema / properties / origin / description
      Previous value: -"Origin header value to include in the preflight, e.g. https://app.example.com. Defaults to https://domainposture.com if omitted."New value: +"Origin header to send, e.g. https://app.example.com. Defaults to https://domainposture.com."
  2. Changed1 schema field changed
    • changedInput schema / properties / origin / description
      Previous value: -"Origin header value to include in the preflight, e.g. https://app.example.com. Defaults to https://drwho.me if omitted."New value: +"Origin header value to include in the preflight, e.g. https://app.example.com. Defaults to https://domainposture.com if omitted."
  3. Changed3 schema fields changed
    • changedInput schema / properties / domain / description
      Previous value: -"Public FQDN."New value: +"Public FQDN, e.g. example.com. Must be resolvable on the public internet; IPs, ports, paths, and protocol prefixes are rejected."
    • changedInput schema / properties / method / description
      Previous value: -"Access-Control-Request-Method; default GET"New value: +"Access-Control-Request-Method header value, e.g. POST or PUT. Defaults to GET if omitted."
    • changedInput schema / properties / origin / description
      Previous value: -"Origin header to send; default https://drwho.me"New value: +"Origin header value to include in the preflight, e.g. https://app.example.com. Defaults to https://drwho.me if omitted."
  4. Added

TDQS

A4.5/5.0
Behavior5/5

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

Beyond the readOnlyHint and openWorldHint annotations, the description discloses operational details: it sends exactly one OPTIONS request, has a 5-second timeout, targets https://<domain>/, and returns a status field with specific success, not_applicable, timeout, and error shapes. It also tells the agent how to interpret the result, which is valuable behavioral context.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is compact and information-dense: purpose, request behavior, timeout, response envelope, and result interpretation in three sentences. It is front-loaded with the action, and every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description fully documents the response format and status variants, including field names and fallback behaviors. Combined with complete parameter coverage in the schema, an agent has everything it needs to invoke and interpret this tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already explains domain, method, and origin meaning and defaults. The description adds only a general reference to 'given origin and method' without new details, so the baseline of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb ('Send a CORS preflight') and a clear resource (https://<domain>/), then explains the purpose: checking whether a site accepts cross-origin requests from a given origin and method. It differentiates itself from sibling tools like dossier_headers by focusing on CORS preflight behavior and access-control-* headers.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly states when to use the tool: 'Use to check whether a site accepts cross-origin requests from a given origin and method.' It also provides interpretation guidance for the not_applicable and error statuses. It doesn't state exclusions or alternatives, but no close sibling requires such a contrast.

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

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