Saydo MCP Server

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║                               does the tool do what it says                                ║
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DRAFT COPY — pending the owner's pass. Everything below is measured or mechanical, and none of it is a marketing claim, but the wording has not been approved.

A publisher declares, in a signed machine-readable contract, exactly what a tool does. A harness makes the tool run and checks it against that contract. Every run emits a hash-chained receipt anyone verifies in a browser, with no account, and without trusting the issuer.

The question it answers is narrow on purpose: does this tool do what it says? Not is it safe, not is it good. A tool that refuses to act has not been shown to be safe — it has not been shown anything, and SayDo says that in those words rather than returning a green tick.

What a verdict can be

pass          the declared behaviour held under the run
fail          the tool did something it declared it would not
not-covered   the run established nothing either way

not-covered is never quietly upgraded to pass. Most of the interesting failures in this domain come from silence being read as good behaviour.

And a whole run resolves to one of four things, not two:

CONFORMANT      it did what it said, and it was shown doing it
NOT CONFORMANT  it did something it declared it would not
INCONCLUSIVE    nothing failed, and nothing was established
(revoked / expired, once a registry has spoken)

INCONCLUSIVE carries most of the weight. A server that declines every call — the commonest kind in the public sweep — makes no network request, writes no file and starts no process, so a naive harness marks all three as passes and issues a warrant for a program that did nothing. SayDo requires a run to have demonstrated conduct before any of those checks can pass, and a server describing itself does not count as conduct.

In your CI

- uses: vince-gonzalez/saydo@main
  with:
    command: python -m my_server
    declaration: saydo.declaration.json

The build fails if the tool breaks its declaration, and also if the run established nothing — because a green check that proves nothing is worse than no check, being a claim of conformance that nobody actually made. Set require-coverage: false to let such a build through; the receipt still records it as inconclusive and never as a warrant.

This is the place the tool is worth the most. Coverage comes from the tool actually doing its work, which needs the credentials and inputs it accepts — and those exist in the publisher's own CI and essentially nowhere else.

Run it on anything

saydo puts one tool under test and writes a receipt. The tool does not have to be yours, and it does not have to be an F-Keys one:

python cli/saydo.py verify --npm  @modelcontextprotocol/server-memory --sandbox
python cli/saydo.py verify --pypi mcp-server-time --sandbox
python cli/saydo.py verify --command "python my_server.py" --declaration mine.json

With --declaration, the author's own contract is the thing being tested. Without one, a deliberately conservative contract is inferred and most invariants come back not-covered — the honest result for a stranger poking at a server they have no credentials for.

--sandbox runs the server inside a container whose only route out is a recording proxy (Linux and Docker; the containment is proven in CI, and tools/SANDBOX.md states plainly what it does and does not cover). Without it the run is observed, not enforced, and the receipt says observed, so no claim can outrun the mechanism that produced it.

Then check the result yourself:

python cli/saydo.py status certivl        # the one-shot verdict an agent reads
python cli/saydo.py selfcheck             # prove the harness can fail

Open verifier/index.html, paste in the receipt and the anchor, and the page recomputes the entire chain and the signature in your browser. No request leaves it.

The four layers

1  declaration   what the publisher promises, signed  (spec/)
2  harness       makes the tool act, and watches      (tools/harness.py)
3  receipt       hash-chained, signed, verifiable     (tools/receipt.py)
4  registry      what is still true, and until when   (tools/registry.py)

Layer 4 exists because a receipt is a fact about one moment, and left there it answers the wrong question. Nobody choosing a tool wants to know it behaved in August. Claims therefore expire at read time, so nothing stays green merely because no one re-ran it, and a revocation is sticky: publishing a newer passing receipt over a withdrawn claim records the attempt and does not lift the withdrawal.

Two things here that are not standard practice

The counterfactual. Watching a tool make a network call tells you it made a call. It does not tell you whether your data left. So the tool is run twice with different inputs, and each destination is classified by whether what it received changed with the input: input-dependent means the payload carried what you gave it, input-independent means it did not, and an opaque body is reported unexamined rather than clean. It sent your input to example.com is a different sentence from it made a request, and only the first one is worth anything to the person deciding.

Drift. A tool redefined under an unchanged version number looks completely ordinary in any single receipt; the deception exists only as a difference between two runs. Receipts therefore chain to their predecessor, and a redefinition with no version change is graded serious rather than noted.

This one is not unusual, and it was listed here as though it were until a proper look at the field turned up several projects doing it — see Adjacent work below. askalf/truecopy pins a vetted tool definition by content hash and fails a CI run when the bytes change, which is drift detection by another name and shipped before this. The distinctive claim is narrower than it first appeared: the counterfactual above, and testing behaviour against a contract the author wrote, rather than checking that the bytes are the ones you vetted.

Layout

spec/                  the declaration schema and its field semantics
tools/harness.py       the conformance harness      (tools/HARNESS.md)
tools/runner.py        local vs contained execution (tools/SANDBOX.md)
tools/egress_proxy.py  recording proxy, allowlist enforcement, TLS inspection
tools/canary.py        marker generation and body examination
tools/differential.py  the two-run counterfactual classifier
tools/drift.py         what changed since the previous receipt
tools/registry.py      expiry and sticky revocation
tools/status.py        receipt -> the compact object an agent reads
tools/declare.py       draft a declaration from an observed run
tools/discover.py      find MCP servers on npm and PyPI
tools/sweep_scale.py   measure many of them, in batches
action.yml             SayDo as a GitHub Action
verifier/index.html    self-contained browser verifier, no network
seeded/malserver.py    a server built to lie, so the harness can be tested
seeded/silentserver.py a server that declines everything, so the harness
                       can be tested against reporting silence as clean

Verify the verifier

selfcheck runs a seeded server that breaks six of its own promises on purpose. If the harness reports it conformant, or attributes a finding to the wrong invariant, then the harness is broken and no receipt it has ever produced is worth anything. The declaration validator is checked the same way, against five mutations it must reject.

A second fixture does the opposite and matters just as much: it starts, lists its tools, and declines every call. The harness must report that as INCONCLUSIVE. When it reported CONFORMANT — which it did, and the receipt was signed — the mark meant nothing, since that is what most public MCP servers do when a stranger calls them.

CI asserts both, on the library and on the Action: a build must fail on a tool that lies, and on a run that shows nothing.

A check that cannot fail for the reason you care about is not a check.

Prior art this builds on

• TBOM v1.0.2, Jason M. Lovell, 2026 — 10.5281/zenodo.18459260
• CTMS 1.0, George Kanellopoulos, 2026 — github.com/gkanellopoulos/ctms

Both are provenance: they establish that tool metadata is what the publisher released, and both state that verifying behaviour against that metadata is out of their scope. That out-of-scope line is what this repository is for. A SayDo declaration attaches through TBOM's existing attestations[] and reuses its ToolDigest format, so nothing here forks either of them.

Adjacent work, and where the line is

This section keeps growing, which is the useful thing about it. Each of these was found after something here had already been described as unusual, so the list is also a record of claims that had to be narrowed.

• Pipelock, github.com/luckyPipewrench/pipelock — an agent firewall that mediates a running agent's traffic and emits signed receipts.
• truecopy, github.com/askalf/truecopy — vets a tool definition, pins it by content hash with an optional Ed25519 signature, and fails CI when the bytes change. Paired with redstamp for runtime containment.
• Proofpane, github.com/Proofpane/releases — a governance proxy recording every tool call to a hash-chained audit log, exported as an Ed25519-signed, offline-verifiable evidence pack. Closed source; that repository is a download mirror.
• dcl-webhook, github.com/Fronesis-Labs/dcl-webhook — policy verdicts written to a tamper-evident SHA-256 hash chain.

The line is not the cryptography. A hash-chained, signed, offline-verifiable record is now a common design, and this repository does not claim otherwise.

The line is what the record is about. Pipelock and Proofpane attest to actions a deployed agent took. truecopy attests that a tool is the same bytes you vetted — integrity, which catches a silent update and is silent about a tool that was always misbehaving. A SayDo receipt attests that one version of one tool did what its author said it would, tested by running it, against a contract written before the run.

Integrity asks is this the thing I approved? Conformance asks does the thing do what it claims? Both are worth having, and neither answers the other.

What still appears to be unshared, on the evidence gathered so far: the two-run counterfactual that separates your data left from a request happened, and refusing to call a tool clean when it merely declined to act. If either turns out to have prior art, it belongs in this list and the claim above should be cut rather than defended.

Status

Public working repository. Receipts produced here are signed with a proof-of-concept key held by F-Keys Creative LLC; production signing is not settled. The corpus measurements are a draft pending the owner's pass, and every figure in them is a lower bound — servers were run without credentials, so a credentialed server may do more than was recorded.

Licence: the open layers — the declaration schema and spec text (spec/), the reference tooling (tools/), the browser verifier (verifier/), and the seeded fixture (seeded/) — are Apache-2.0 (see LICENSE, NOTICE). Signed public artifacts are not placed under any licence by this repository.

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║               ·   C  R  E  A  T  I  V  E   ·               ║
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║          ────────────────────────────────────────          ║
║                                                            ║
║                      Vincent Gonzalez                      ║
║                         f-keys.com                         ║
║                 ORCID 0009-0005-3640-014X                  ║
║                                                            ║
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