Tiltmeter

Tiltmeter

An early-warning system for the third-party APIs your AI agents depend on, with the fix as a pull request. · tiltmeter.dev

Volcanologists bolt tiltmeters to the ground to sense tiny deformations long before an eruption. Tiltmeter does the same for the APIs under your agents. It learns the shape of their JSON responses from real traffic, notices when a vendor renames a field, starts sending null or turns a number into a string, and tells you, your CI and the agents themselves before anything goes on tilt. Then tiltmeter fix hands the change to an agent that adapts the code reading that API and opens the pull request, leaving what it cannot know for a human.

Typed code crashes loudly when an API changes. Agents don't. They read the new response, fill the gaps with guesses, or retry until the budget is gone.

Highlights

• Agents can check before they act. An MCP server lets Claude Code, Cursor, LangChain or any MCP client call has_drifted before trusting an API, and get_schema to see which fields to expect.
• No spec required. Tiltmeter learns from real responses, so it works with any JSON API, documented or not.
• Breaking or harmless, at a glance. Every change is classified as breaking, warning or info, and a removed field next to a similar new one is flagged as a probable rename.
• Explanations on demand. With an Anthropic API key, Claude explains what changed, the likely cause and what to do about it.
• Fixes, too. tiltmeter fix hands the drift to an agent that adapts the code reading that API, shows you the diff and opens a pull request. Use the built-in LangChain Deep Agent, or your own Claude Code or Codex login.
• Provider mode. API providers announce a change once, in a signed notice on their own domain, and every customer that follows them gets the pull request before the old responses stop. No server in between.
• A CI gate with alerts. Exit codes fail the build on breaking drift. Slack and webhook alerts take one line of config.
• Local and private. One SQLite file and no account. Credentials are expanded at request time and never stored. Response bodies are not stored or sent to the LLM, only their shape.

Quickstart

First, see which API changes that already shipped your code still uses, with nothing to set up:

$ uvx tiltmeter scan

✗ api.groq.com Groq no longer serves 16 models it retired, the latest on August 16, 2026. took effect 2026-08-16 groq-retired-models-2026-08 · unsigned: drafted by Tiltmeter from the provider's public documentation src/llm.js:37 llama-3.1-8b-instant: retired; use openai/gpt-oss-20b groq: 'llama-3.1-8b-instant', src/store.js:108 llama-3.3-70b-versatile: retired; use openai/gpt-oss-120b groq: { fast: 'llama-3.1-8b-instant', smart: 'llama-3.3-70b-versatile' }, fix: tiltmeter fix --notice groq-retired-models-2026-08 --allow-unsigned --repo .

1 of 10 known API changes affects .: 2 lines in 2 files.

It searches the folder for every entry of a catalog of known changes (retired models at Anthropic, OpenAI and Groq, Stripe's moved subscription periods, Jira's removed search, and more), drafted by Tiltmeter from each provider's public documentation. It records nothing and sends nothing.

Then watch the APIs you call, so the next change does not wait for a catalog:

pip install tiltmeter        # or: uv tool install tiltmeter

tiltmeter init # writes tiltmeter.yaml with a public example API tiltmeter check # the first check records the baseline

Already calling an API from a web app? Export a HAR from your browser's DevTools (Network tab, "Export HAR") and let Tiltmeter write the config from the JSON calls the page made. Tokens and cookies become ${VAR} placeholders:

tiltmeter init --from-har session.har --host api.example.com

Run tiltmeter check again from cron or CI, or leave tiltmeter watch running. This is what you get when a vendor renames phone and turns balance into a string:

$ tiltmeter check

✗ billing_customers 200 · 13 ms BREAKING · 3 changes breaking type_changed $.data[*].balance integer → string breaking field_removed $.data[*].phone string → (absent) possibly renamed to $.data[*].phone_number info field_added $.data[*].phone_number (absent) → string possibly replaces $.data[*].phone 1 endpoint checked · 1 breaking $ echo $? 2

The getting started guide runs that exact scenario against a fake API on your machine in about five minutes.

Give your agents a tiltmeter

claude mcp add tiltmeter -- tiltmeter serve --config /absolute/path/to/tiltmeter.yaml

Then add a line like this to your agent's instructions:

Before you rely on a third-party API, call has_drifted for it. If it drifted, read the

summary and adapt before trusting the response.

Setups for Cursor, Claude Desktop and LangChain agents are in the agents guide.

Let it fix your code

When a check finds drift, tiltmeter fix hands it to an agent that finds the code reading that API, adapts it, shows you the diff and opens a pull request:

$ pip install "tiltmeter[fix]"            # or plain tiltmeter, then --agent claude-code or codex

$ tiltmeter fix 2 --repo ~/code/billing-service ✗ billing_customer #2 200 · 10 ms BREAKING · 3 changes Working on a new branch, tiltmeter/fix-billing-customer-2, from main at 162dadd. 3 files changed +5 -5 diff --git a/billing/client.py b/billing/client.py

• return f"{customer['name']} <{customer['phone']}>"
• return f"{customer['name']} <{customer['phone_number']}>"

... Commit, push and open a pull request? [y/N]: y ✓ opened https://github.com/acme/billing-service/pull/41

• Your checkout is never touched. The agent works in a temporary git worktree on a new branch, and nothing is committed until you approve the diff or pass --yes.
• It stays inside the worktree. No network access, and only tracked files are there to read; .env files, keys and .git are blocked. The built-in agent and Claude Code get file tools only. Codex keeps its shell, locked in its OS sandbox under the same limits.
• It says what it could not do. Tiltmeter sees types, not values. When a number turns into a string, the agent updates the types and leaves the format question to a human in the pull request instead of guessing a conversion.
• Bring your own agent. Already use Claude Code or Codex? tiltmeter fix 2 --agent claude-code or --agent codex runs on your own login, with no API key and no extra install.

--dry-run shows the diff and throws it away, and --no-pr commits to a local branch. Before anything is committed, Tiltmeter warns about changed files that nothing else in the repository imports, and keeps a fix that only touches such code, unchanged for months, in a local commit unless you pass --allow-unused. The fix guide covers the flags, what the model sees and how to review the result.

Provider mode

Providers shouldn't just announce changes; they should apply them. A provider describes a change once, in an API change notice: a small signed JSON file in Tiltmeter's vocabulary, served from its own domain next to its public key. Customers follow the provider, and each one gets a pull request that adapts its own code.

# The provider, from two versions of its spec (or from a check of its staging API):

$ tiltmeter notice create --from-openapi v2.yaml v3.yaml --effective 2026-12-01 -o notice.json $ tiltmeter notice sign notice.json --key api-change-key.pem $ tiltmeter notice publish notice.json --feed site/.well-known/api-changes.json

Each customer, on a schedule (the GitHub Action does it for you):

$ tiltmeter notices apply --repo . --yes ✓ opened https://github.com/acme/billing-service/pull/42

• api.other.example 2026-11-20-invoices not affected: no tracked file mentions api.other.example

• Only signed notices act. The signature is checked against the key the provider serves at /.well-known/api-change-key, and every endpoint in the notice must be on the provider's domain.
• No agent when nothing is affected. A plain text search for the API's host, paths, SDKs and the changed field names decides first, so repositories that don't use the API cost nothing and get nothing.
• Same sandbox, same review. The fix runs like tiltmeter fix, and the pull request quotes the provider as plain text and lists what is left for a human.

• Works before providers do. A provider that publishes no notices but an OpenAPI spec can be followed directly: Tiltmeter keeps its last version, finds what changed in its responses, and handles it like a notice.
• For providers, from CI. Every pull request that changes your spec gets a draft notice as a comment; merging signs and publishes it.

Field report, October 2026. We searched public code for fields that Stripe and Spotify removed. 78 repositories still read Stripe's subscription.current_period_end, gone since API version 2025-03-31, and 228 use Spotify fields and endpoints that changed for new apps in February 2026. One of them was Stripe's own subscription sample, which no longer type-checks against Stripe's SDK. Tiltmeter fixed it and 14 others we checked by hand, and the pull requests are open: the fix for Stripe's sample.

Since then Tiltmeter has opened 84 pull requests for changes at Stripe, Jira, Spotify, OpenAI, Anthropic, Groq, Slack, OpenWeatherMap, Hugging Face and HubSpot. So far 18 have landed: 15 were merged as Tiltmeter wrote them, and 3 were adopted by maintainers who landed the fix themselves. inbox-zero and QOwnNotes carried Tiltmeter's commit into changes of their own, and aicommits made the same change in its own commit. OpenMetadata picked up Tiltmeter's commit in [its own pull request](https://github.com/open-met