customer.io WebMCP audit

Name: customer.io WebMCP audit
Creator: ora

Rescan

audited Aug 28, 2026in 6s

37/ 100

3 tools registered. Strongest in WebMCP use, weakest in human experience.

WebMCP use55

Usefulness33

Human experience0

about:blank

No agent run recorded yet.

No steps recorded

Tools

open_customerio_page

Navigate to a key Customer.io page — product overview, pricing, AI, (developer/agent-focused), features, integrations, customer stories, security, or documentation.Takes an action on the site.

pagehttps://customer.io/

implementation

viaimperative

entry pointnavigator

registered after1695ms

executepresent

api surface

pagerequired

annotations

read onlynot declared

destructivenot declared

idempotentnot declared

open worldnot declared

untrusted contentnot declared

titlenot declared

4 findings

failCanonical entry point

0 / 4

Every tool registers through the deprecated navigator.modelContext alias; move them to document.modelContext before the alias is removed.

fix

// Use the canonical entry point - navigator.modelContext is deprecated.
document.modelContext.provideContext({ tools: [/* ... */] });

warningNaming quality

1.3 / 2

Tool naming makes selection harder than it needs to be: 2 names do not start with a verb (open_customerio_page).

fix

{ name: "open_customerio_page" /* short, unique, verb-based */ }

failAnnotations present

0 / 4

3 of 3 tools declare no readOnlyHint, so an agent cannot tell a read from a write without guessing from the name.

open_customerio_page, start_customerio_free_trial, contact_customerio_sales

fix

{
  name: "open_customerio_page",
  annotations: { readOnlyHint: true, destructiveHint: false, idempotentHint: true }
}

warningHuman parity

0 / 8

3 of 3 tools run through the JavaScript API with no visible counterpart, so the person co-browsing cannot see what the agent is offered. Declarative forms (or at least a title annotation) close the gap.

open_customerio_page, start_customerio_free_trial, contact_customerio_sales

fix

<!-- Give the tool a visible counterpart: a declarative form is one the person can see and use too. -->
<form toolname="open_customerio_page" tooldescription="...">
  <!-- the same action, as UI -->
</form>

tool json

{
  "name": "open_customerio_page",
  "description": "Navigate to a key Customer.io page — product overview, pricing, AI, (developer/agent-focused), features, integrations, customer stories, security, or documentation.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "page": {
        "type": "string",
        "enum": [
          "home",
          "platform",
          "pricing",
          "ai",
          "features",
          "integrations",
          "customers",
          "security",
          "docs"
        ],
        "description": "Which Customer.io page to open."
      }
    },
    "required": [
      "page"
    ],
    "additionalProperties": false
  },
  "annotations": {}
}

Findings

WebMCP use

55 / 100 · weight 50

passTools registered

4 / 4

3 tools registered across 1 page.

failReal-browser eligible

0 / 8

The page's code registers these tools, but a real visitor's browser does not get them yet: WebMCP needs a native modelContext or a current origin trial token, and this page has neither.

warningRegistration timing

2 / 4

The slowest tool took 1695.3000001907349ms to register, past the 1000ms an agent reading the registry at first paint would wait for.

toolstart_customerio_free_trial

start_customerio_free_trial: registered at 1695.3000001907349ms

fix

// Register tools as soon as they're ready, not behind a deferred/async chunk.
document.modelContext.provideContext({ tools: [/* ... */] });

failCanonical entry point

0 / 4

Every tool registers through the deprecated navigator.modelContext alias; move them to document.modelContext before the alias is removed.

toolopen_customerio_page

fix

// Use the canonical entry point - navigator.modelContext is deprecated.
document.modelContext.provideContext({ tools: [/* ... */] });

passSchema validity

5 / 5

All 3 tools declare a structurally valid object input schema.

passSchema quality

4 / 4

All 3 tool schemas describe their parameters and stay within Chrome's size guidance.

passStub detection

5 / 5

All 3 tools declare an execute handler.

failAnnotations present

0 / 4

3 of 3 tools declare no readOnlyHint, so an agent cannot tell a read from a write without guessing from the name.

toolopen_customerio_page

open_customerio_page, start_customerio_free_trial, contact_customerio_sales

fix

{
  name: "open_customerio_page",
  annotations: { readOnlyHint: true, destructiveHint: false, idempotentHint: true }
}

not applicableAnnotation mismatch

0 / 3

No tool declares a readOnlyHint, so there is no safety claim to contradict.

not applicableUntrusted content hint

0 / 2

No tool's contract suggests it returns text written by somebody other than the site, so there is nothing to flag as untrusted.

passRegistration errors

2 / 2

No tool registration threw during the capture.

warningToolchange coherence

1 / 2

3 tools were registered but the page never dispatched a toolchange event, so an agent subscribed to registry updates never learns they exist.

fix

document.modelContext.dispatchEvent(new Event("toolchange"));

not applicableInjection surface

0 / 3

The injection-surface model hop returned no usable result, so tool contracts were not reviewed for injection surface.

Usefulness

33 / 100 · weight 30

warningNaming quality

1.3 / 2

Tool naming makes selection harder than it needs to be: 2 names do not start with a verb (open_customerio_page).

toolopen_customerio_page

fix

{ name: "open_customerio_page" /* short, unique, verb-based */ }

not applicableDescription quality

0 / 6

The description-quality model hop returned no usable result, so descriptions were not rated.

not applicableTool selection

0 / 14

The tool-selection model hop returned no usable result.

failCoverage vs. site type

2 / 8

The tool set covers 1 of the 4 things an agent needs on a saas site; it cannot search or browse the catalog or read one item in detail or update or move an existing record.

Human experience

0 / 100 · weight 20

warningHuman parity

0 / 8

toolopen_customerio_page

open_customerio_page, start_customerio_free_trial, contact_customerio_sales

fix

<!-- Give the tool a visible counterpart: a declarative form is one the person can see and use too. -->
<form toolname="open_customerio_page" tooldescription="...">
  <!-- the same action, as UI -->
</form>

not applicablePage experience

0 / 12

The page-experience model hop returned no usable result, so the page was not graded.

Tool selection

The tool-selection model hop returned no usable result.

how this was captured

chrome: 148.0.7778.96
capture shim: v1
spec snapshot: 2026-08
mode: fast
pages: 1
tools: 3
run time: 6s
finished: Aug 28, 2026