WebMCP in production|INEMA.CLUB-PRO

Lesson 6 · 15 min

Living with an API that changes: watch the spec, Chrome Status and the MCP changelog

The WebMCP API has already moved once: from navigator to document. It will change again before any stable release. Instead of finding out from a visitor, record what the sources said on the day the test suite passed and let a script compare. Changed? Run the test suite and read it before touching anything.

Start the lesson
A person seen from behind in front of a monitor showing two versions of a technical document side by side, with a magnifying glass on the desk.

In this lesson you will

  1. 1The timeline of the navigator → document switch
  2. 2What to watch: spec, Chrome Status, MCP and the SDK
  3. 3The recorded baseline and the comparison
  4. 4What to do when the watch says MUDOU

Goal: record the baseline from the day the test suite passed and watch the spec, Chrome Status and MCP, with the navigator → document case as an example.

01An API that has already changed

Dates read from primary sources on 10/19/2026. Click each milestone.

Click each block in the diagram to see what it does.

02What to watch and where

Public pages, no key and no cost.

1. Spec

The date at the top of the draft and the IDL names (registerTool, getTools, executeTool, toolchange).

Old name coming back or a new method showing up: time to reread.

Sourcewebmachinelearning.github.io/webmcp

03The saved baseline

Generated with --gravar on the day the battery passed. This is what the watcher compares against.

File · kit/vigia/base.json
{
  "gravada_em": "2026-10-19",
  "spec_data": "2026-10-16",
  "spec_superficie": "document",
  "spec_metodos": "registerTool getTools executeTool toolchange",
  "chrome_status": "Proposed",
  "chrome_origin_trial": "149–156",
  "mcp_versao_atual": "2026-07-28",
  "sdk_mcp_anuncia": "2026-07-28"
}

04Watch

Reads the sources now and compares. With no network, it exits with 3 and concludes nothing.

Terminal · watcher against the kit's baseline
cd ~/projetos/formacao-webmcp-expert-v72/kit
node scripts/vigiar.mjs; echo "saída: $?"
Example from the repository
vigia · base de 19/10/2026 (vigia/base.json)
igual     spec_data            2026-10-16
igual     spec_superficie      document
igual     spec_metodos         registerTool getTools executeTool toolchange
igual     chrome_status        Proposed
igual     chrome_origin_trial  149–156
igual     mcp_versao_atual     2026-07-28
igual     sdk_mcp_anuncia      2026-07-28
VIGIA: 7/7 iguais à base · nada a fazer
saída: 0

If you run it after 10/19/2026 and MUDOU shows up, the watcher is doing its job: run the battery and read the change.

05Compare with the old course's baseline

A baseline with only what the old course recorded (spec date and surface). The rest shows up as "sem base".

Terminal · base as of 09/24/2026
cd ~/projetos/formacao-webmcp-expert-v72/kit
node scripts/vigiar.mjs --base vigia/base-curso-antigo.json; echo "saída: $?"

06Practice

Watch, see a real change, and save your own baseline. Each exercise ends in a done when.

E1 · Watch against the kit's baseline

3 min

Run the watch. If MUDOU shows up, note what it says: that is the warning working.

Done when: node scripts/vigiar.mjs; echo "saída: $?" → VIGIA: 7/7 iguais à base · nada a fazer and saída: 0 as long as nothing has changed since 10/19/2026; with a change, MUDOU lines and saída: 1.

E2 · The change the old course missed

3 min

Run the watch against the 09/24/2026 baseline.

Done when: The output has MUDOU spec_data 2026-09-17 → 2026-10-16 and saída: 1.

E3 · Your baseline

10 min

After the battery passes on your project (lesson 4), save your baseline and mark the next watch and the end of the origin trial (Chrome 156) on your calendar.

Done when: node scripts/vigiar.mjs --base vigia/minha-base.json --gravar → base gravada em vigia/minha-base.json, and the calendar has both dates.

07Lesson quiz

The explanation appears after the answer.

Question 1 of 4

The watch came back with MUDOU spec_data. What is the right order?

08In three sentences

ChangesThe API has already switched from navigator to document and will change again before any stable release.
BaselineSave what the sources said on the day the battery passed.
WatchIt changed: battery, reading, fix; only then are the baseline and the battery re-saved.

Going further

WebMCP spec: commit historyChrome for Developers: WebMCP origin trialMCP: versioningMCP Registry (preview)
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