# One row of SQL is the whole contract for a capability, and the 892nd took 3.1 seconds slug: directory-row-contract · https://miscsubjects.com/a/directory-row-contract · tags: tooling, oip, architecture, d1, contracts, mcp · updated 2026-07-26T03:52:45.831Z A capability on this build is one row in a SQLite table on Cloudflare D1 called `directory`. The row is the whole contract: what the capability is, how to call it, what comes back, which credential it needs, and who is allowed to run it. There is no companion file, no registration call in application code, and no deploy step. On 2026-07-26 the table held 891 rows. **Scope note:** this article covers the `directory` table's row shape only — the contract for API calls, shell commands, agents and other executable capabilities. It is one of at least two object families on this build; content (articles, their claims, their revisions) lives in a separate `articles`/`article_slots` pair of tables with its own resolver, not in `directory`. [892 rows, 8 of them MCP](/a/the-directory-is-not-the-object-system) draws that line explicitly. Every field below is published rather than paraphrased, every runner type has a real row printed as stored, and the failure strings are copied out of the code that emits them. The volume argument — why holding 891 tool definitions in a model's context is the wrong shape — is [tooling as data](/a/tooling-as-data). The call sequence around a row is [the four-step loop](/a/dispatch-four-step-loop). The Model Context Protocol view of the same rows is [MCP as a projection](/a/mcp-as-a-projection). ## Evidence status **Observed** marks first-party measurements or runtime receipts from the named environment. **Derived** marks arithmetic calculated from cited inputs. **Specified** marks vendor or standards documentation. **Implemented** and **deployed** name code and live-state evidence, respectively. **Reproduced** means the stated procedure was rerun. **Externally attested** marks operator reports; those reports show that an experience occurred, not that it is universal. ## Eighteen columns, of which six existed on the first day The table as it stands in production. Read it back yourself: ```bash cd /Users/owner/miscsubjects-pages npx wrangler d1 execute loop-content-spine --remote \ --command "SELECT sql FROM sqlite_master WHERE name='directory';" ``` ```sql CREATE TABLE directory ( key TEXT PRIMARY KEY, type TEXT NOT NULL CHECK (type IN ('fn','http','agent','flow')), target TEXT, auth TEXT, content TEXT, updated_at TEXT NOT NULL , category TEXT, allowed_categories TEXT, seq INTEGER, enabled INTEGER DEFAULT 1, planner_visible INTEGER DEFAULT 1, planner_rank INTEGER DEFAULT 100, input_schema TEXT, examples TEXT, sensitive INTEGER DEFAULT 0, runner TEXT, includes TEXT, created_at TEXT) ``` The first six columns came from `migrations/0007_directory.sql:1-8`. Everything after the closing parenthesis of the original statement is an `ALTER TABLE` bolted on later, which is why the SQL reads the way it does. | Column | Type · default | Required | What it holds | Real value | | --- | --- | --- | --- | --- | | `key` | TEXT, primary key | yes | The invocation name. Unique by constraint, uppercase by convention. | `GROK_MODELS` | | `type` | TEXT, `CHECK IN ('fn','http','agent','flow')` | yes | Decides how `target` and `content` are read. The only constrained column in the table. | `http` | | `target` | TEXT | by type | `fn`: a function name. `http`: `"METHOD url"`. `agent`: a model id. `flow`: empty. | `GET https://api.x.ai/v1/models` | | `auth` | TEXT | no | The *name* of an environment variable and how to apply it. Never a secret value. | `bearer:GROK_API_KEY` | | `content` | TEXT | yes, gated | `fn`/`http`: comment docstring plus the argument template. `agent`: the system prompt. `flow`: the step DSL. | see the four rows below | | `updated_at` | TEXT, NOT NULL | yes | ISO timestamp of the last write. The only change marker on the row. | `2026-06-10 02:22:52` | | `category` | TEXT | no | Grouping label. 110 distinct values live. | `grok` | | `allowed_categories` | TEXT | no | On `agent` rows: the categories that agent's tool listing is restricted to, or `*`. | `*` | | `seq` | INTEGER | no | Manual ordinal used to pin a row to a position. Null for almost every row. | `null` | | `enabled` | INTEGER, default 1 | no | `0` hides the row from every projection. 13 rows are disabled. | `1` | | `planner_visible` | INTEGER, default 1 | no | Whether planners and the MCP projection list it. | `1` | | `planner_rank` | INTEGER, default 100 | no | Sort weight for candidate selection. Lower wins. | `100` | | `input_schema` | TEXT | no | JSON Schema string, used when the row is projected as a typed tool. 256 rows carry one. | `null` | | `examples` | TEXT | no | JSON array of worked argument strings. 63 rows carry one. | `["37.77\|-122.42"]` | | `sensitive` | INTEGER, default 0 | no | `1` routes the call through the watcher before it runs. 227 rows are marked. | `0` | | `runner` | TEXT | no | Overrides the runner inferred from `type`. 301 rows have a value. | `null` | | `includes` | TEXT | no | On `agent` rows: comma-separated prompt-block keys composed in front of `content` at runtime. | `BLOCK_VOICE,BLOCK_REASONING_A` | | `created_at` | TEXT | no | Present in the live table. **No migration in the repo adds it.** | `null` on old rows | | `row_num` | computed, not stored | — | 1-based position in the canonical ordering, attached by the read path. | `412` | Column provenance, by migration: `0012_directory_category.sql:7-9` added `category`, `allowed_categories`, `seq`. `0018_planner_columns.sql:5-9` added the five planning and schema columns. `0064_substrate.sql:5` added `runner`. `0118_add_directory_sensitive.sql:2` added `sensitive`. `0183_prompt_blocks.sql:2` added `includes`. `created_at` has no such line — `grep -rn "ALTER TABLE directory" --include="*.sql" .` returns fourteen matches and none of them mention it, so that column entered the production table out of band. A rebuild should add it in a migration. Two columns exist in the table but cannot be written through the REST surface. The PATCH handler's field allow-list at `functions/api/directory/[key].js:223` contains thirteen names, and neither `sensitive` nor `runner` is one of them: ```bash curl -sS -X PATCH "https://miscsubjects.com/api/directory/ZZ_TEST_TEMPERATURE" \ -H "x-terminal-key: $TERMINAL_KEY" -H 'content-type: application/json' \ -d '{"runner":"edge"}' # {"error":"no recognized fields"} HTTP 400 ``` ## The type column decides everything else, and it has exactly four legal values `fn` runs a function inside the build's own Worker. `http` calls somebody else's API. `agent` sends `content` to a model as a system prompt. `flow` chains other rows. The dispatcher branches on the column at `functions/api/dispatch.js:1145-1156`; a fifth value is rejected by the `CHECK` constraint before that branch is reached. | Type | Live rows | `target` holds | `content` holds | Pick it when | | --- | --- | --- | --- | --- | | `fn` | 480 | a key into the runner map | a JSON array template of the function's positional arguments | the work is code you control and want to run at the edge | | `http` | 303 | `"METHOD url"`, with `$1` slots | the request body template, or nothing for GET | the work is an existing API | | `agent` | 57 | a model id, e.g. `grok-4.3` or `gw:openai/gpt-4.1-mini` | the system prompt | the work needs judgement, not a deterministic call | | `flow` | 51 | empty string | steps separated by `>`, each `KEY: args` | the work is two or more capabilities in order | Counted live: ```bash npx wrangler d1 execute loop-content-spine --remote \ --command "SELECT type, COUNT(*) AS n FROM directory GROUP BY type ORDER BY n DESC;" # fn 480 | http 303 | agent 57 | flow 51 → 891 ``` One real row of each type, exactly as stored. **`fn` — `NOW`** ``` key NOW | type fn | target now | auth (null) | category time content # Return the current time from the build clock in Pacific time (America/Los_Angeles). # WHEN_TO_USE: any object or model that needs the current date or time. # ARGS: none # EX: [NOW][/NOW] # OUTPUT: { now, today, time, zone, iso } — Pacific-offset ISO; today is the Pacific calendar date. ``` Every line of `content` beginning with `#` is stripped before execution by `stripDocs` at `dispatch.js:440-452`. What is left is the executable payload. `NOW` has no payload line, so `runFn` falls back to the default template `["$1"]` at `dispatch.js:1170`. **`http` — `GROK_MODELS`** ``` key GROK_MODELS | type http | category grok | auth bearer:GROK_API_KEY target GET https://api.x.ai/v1/models content # WHAT: List every model on the xAI API. No args # WHEN_TO_USE: you need to grok models # ARGS: see content # EX: [GROK_MODELS][/GROK_MODELS] # List every model on the xAI API. No args. ``` **`agent` — `PROMPT_LAB_AGENT`** ``` key PROMPT_LAB_AGENT | type agent | target grok-4.3 | auth bearer:GROK_API_KEY content You are a friendly peptide concierge (LAB TEST v1). One warm sentence, then end with [REPLY]your text[/REPLY]. ``` An `agent` row with `includes` composes shared prompt blocks in front of `content` at runtime: `ROUTER` carries `BLOCK_VOICE,BLOCK_IMESSAGE,BLOCK_EMOJI,BLOCK_ROUTING,BLOCK_ARA`, so the voice rules are written once and referenced by six rows. **`flow` — `BLOOIO_FINISH`** ``` key BLOOIO_FINISH | type flow | target (empty) content # Phase C of the inbound turn: given the full agent output text in $1, extract the # LAST [REPLY], send via blooio to $2, return the send result. # $1=agent output text. $2=recipient phone. LAST_REPLY_OF: $1 > SEND_BY_CHANNEL: blooio|$2|$PREV ``` The flow reader splits on a top-level `>` and runs each step against the previous step's output, bound to `$PREV` (`dispatch.js:1686-1731`). A step is `KEY: body`. Appending `=> NAME` binds that step's output to `$NAME` for later steps. A `{ A: x | B: y }` block fans out concurrently. A step whose output starts with `ERR:` stops the flow. ## Arguments are one string, split on the pipe character, and that is a deliberate trade The invocation body is a single string. The dispatcher splits it on `|` and hands the pieces to the runner as `args`: ```js const args = String(body == null ? '' : body).split('|'); ``` That is `dispatch.js:1144`. In a template, `$1` is the first piece, `$2` the second. Two arguments: ```bash curl -sS -X POST https://miscsubjects.com/api/dispatch \ -H "x-terminal-key: $TERMINAL_KEY" -H 'content-type: application/json' \ -d '{"key":"ZZ_TEST_TEMPERATURE","body":"37.77|-122.42"}' ``` `$1` becomes `37.77`, `$2` becomes `-122.42`, and the target `GET https://api.open-meteo.com/v1/forecast?latitude=$1&longitude=$2¤t=temperature_2m` resolves to a real URL. The obvious break: a pipe inside an argument. A JSON body, a prompt, a shell command, a sentence with a pipe in it — the naive split shreds all of them. The handled form is `$N+`, which rejoins arguments N through the end with the pipe put back: ```js if (/^\d+\+$/.test(key)) { const v = args.slice(+key.slice(0, -1) - 1).join('|'); return raw ? v : escFor(mode, v); } ``` `dispatch.js:171-175`. So a row that takes a JSON blob as its last argument uses `$2+`, not `$2`. `DIR_PATCH` is the live example — it edits another row, so its second argument is arbitrary JSON: ``` key DIR_PATCH type http target PATCH https://miscsubjects.com/api/directory/$1 content # ARGS: key | json_body # EX: [DIR_PATCH]ROUTER|{"content":"new prompt text"}[/DIR_PATCH] $2+ ``` Called as `body: 'ROUTER|{"content":"a|b"}'`, the key is `ROUTER` and the body template `$2+` receives `{"content":"a|b"}` intact. The rule that follows: **only the last argument of a row may contain a pipe, and only if the template uses `$N+`.** A row with two free-text arguments in the middle of its signature is unrepresentable, and that is the real cost of the format. Substitution is escape-aware. `subVars` at `dispatch.js:156-201` takes a mode — `url`, `json-string` or `raw` — and escapes each value for the position it lands in, so a quote inside an argument cannot break out of a JSON body template. `$$KEY` skips the escaping. `$PREV` is the previous flow step's output. An unresolved `$NAME` is left in place as literal text rather than becoming an empty string. Why one flat string and not a JSON object per capability: a caller that has read one contract can call any of the 891 without learning a new argument shape, and a router can forward a user's sentence through unchanged. The price is no types at the door. That is the trade one commenter refuses — menix, arguing schemas let a code-writing agent plan one precise program instead of a print-and-inspect loop. Both positions describe real failure modes; the comparison table below lands the verdict. ## The row names the environment variable; the value never enters the table The `auth` column is a prefix and an environment-variable name. `applyAuth` at `dispatch.js:203-234` reads it at call time: | Form | What happens | Live rows | | --- | --- | --- | | empty or null | no credential applied | 637 | | `headers:{"k":"$ENV_NAME"}` | each header value has `$NAME` replaced from the environment | 139 | | `bearer:ENV_NAME` | `Authorization: Bearer ` | 68 | | `basic:ENV_NAME` | `Authorization: Basic ` + base64 of `:` | 45 | | `query:param=ENV_NAME` | appends `?param=` to the URL | 2 | | anything else | throws `ERR:auth:unknown_prefix:` | 0 | ```bash npx wrangler d1 execute loop-content-spine --remote --command \ "SELECT CASE WHEN auth IS NULL OR TRIM(auth)='' THEN '(none)' ELSE substr(auth,1,instr(auth,':')) END AS form, COUNT(*) AS n FROM directory GROUP BY form ORDER BY n DESC;" ``` 115 rows name a credential through `bearer:`, `basic:` or `query:`, and between them they reference **12 distinct auth specifications**. `bearer:GROK_API_KEY` alone appears on 35 rows. One rotation in the platform secret store changes the credential for all 35; no row is touched, no migration runs, no deploy happens. An attacker who exfiltrates the whole table learns every capability that exists, every upstream URL, every argument shape, which capabilities are credentialed, and the *names* of the twelve secrets. That is a real map, worth defending. What they do not get is one credential value, because no column ever holds one. The failure mode of a leaked registry that stores values is total; here it is reconnaissance. The row's claims about permission are advisory. Enforcement is server-side and independent of the row. When an invocation arrives with a scoped capability token, `capGateCheck` at `dispatch.js:2121-2149` evaluates revocation, audience binding, owner gate, contract hash, risk ceiling, fixed body and payload ceiling before any runner is reached. A row marked `sensitive = 1` is denied to any token whose `risk_ceiling` is not `high`, with the literal reason `risk_ceiling:low GROK > GROK_MODELS` | places the row in the tree so a reader can climb to siblings | | Capability / When to use | the `# WHAT` and `# WHEN_TO_USE` lines from `content` | the two questions a caller has before choosing | | RUN NOW | a single URL that fires the example | a model with only a URL-fetch tool can still invoke it | | Example call | `[GROK_MODELS][/GROK_MODELS]` | the router tag form, for a model emitting tags in prose | | type · runner · auth · risk | `tool · edge · grok`, `required · low` | tells the caller whether a credential and an approval are needed before trying | | inputs / outputs | `{"args":"see content"}` and the documented return shape | the argument contract | | Affordances | the moves the presented credential can make | computed for the caller, with the note that the server enforces scope regardless | | Machine Contract | four imperatives, including "do not infer the row shape from memory" | stops a model reconstructing a stale signature from training data | | Invocation / Ledger / Repair | ledger, receipt, replay and repair URLs | closes the loop after the call | | Troubleshooting | four problems, each with an action and a URL | the same content as the failure table below, at the point of use | The contract is close to constant in size regardless of the row. Measured across four rows of four different types: `NOW` 4,423 bytes, `GROK_MODELS` 4,413, `ROUTER` 4,442, `CONTENT_SEARCH` 4,507. The per-row variance is under 100 bytes because the scaffolding dominates and the row-specific part is small — that is the shape of a contract that is fetched one at a time rather than held in context. Fetching all of them at once is the opposite bargain: `curl -s "https://miscsubjects.com/api/dispatch?registry=1" | wc -c` returns 1,608,554 bytes for 877 objects. People running large tool surfaces keep measuring the same thing independently: a maintainer auditing his own agent found 47 tool schemas costing 13,341 tokens on every request before the user's message; a vendor engineer building an MCP server for a large unified API hit 50,000 tokens of definitions before the agent touched a single user message; a tiktoken run against one server's full tool list produced 741 tools and roughly 488,013 tokens, larger than the context window it was meant to fit. ## Adding the 892nd capability: one POST, then a receipt proving it ran Everything below was executed against production on 2026-07-26 using an obviously-named throwaway row, `ZZ_TEST_TEMPERATURE`, which was deleted at the end. The outputs are copied verbatim. **Step 1 — the credential.** `TERMINAL_KEY` is the owner key checked by `isBuildAuthed`. Every mutating call carries it as `x-terminal-key`. ```bash export TERMINAL_KEY="$(grep '^TERMINAL_KEY=' ~/.config/grok-bridge.env | cut -d= -f2 | tr -d '"')" ``` **Step 2 — the POST.** `key` and `type` are the only required fields (`functions/api/directory/index.js:51`). ```bash curl -sS -X POST https://miscsubjects.com/api/directory \ -H "x-terminal-key: $TERMINAL_KEY" -H 'content-type: application/json' -d '{ "key": "ZZ_TEST_TEMPERATURE", "type": "http", "target": "GET https://api.open-meteo.com/v1/forecast?latitude=$1&longitude=$2¤t=temperature_2m", "auth": "", "content": "# WHAT: Current temperature in Celsius for one latitude and longitude, from the Open-Meteo public API.\n# WHEN_TO_USE: a capability needs the live temperature at a coordinate.\n# ARGS: $1=latitude | $2=longitude\n# EX: [ZZ_TEST_TEMPERATURE]37.77|-122.42[/ZZ_TEST_TEMPERATURE]\n# OUTPUT: JSON with current.temperature_2m", "category": "tools", "enabled": 1, "planner_visible": 1, "examples": "[\"37.77|-122.42\"]" }' ``` ```json {"ok":true,"key":"ZZ_TEST_TEMPERATURE","updated_at":"2026-07-26T04:36:19.832Z"} ``` HTTP 201. Without the header the same call returns `{"error":"unauthorized"}` and HTTP 401. **Step 3 — invoke it.** No deploy, no restart, no cache warm-up in between. ```bash curl -sS -X POST https://miscsubjects.com/api/dispatch \ -H "x-terminal-key: $TERMINAL_KEY" -H 'content-type: application/json' \ -d '{"key":"ZZ_TEST_TEMPERATURE","body":"37.77|-122.42"}' \ -w "\nhttp=%{http_code} total=%{time_total}s\n" ``` ```json {"ok": true, "ran": true, "trace": "t_jweoafmw", "result": "HTTP 200:{\"latitude\":37.763283,\"longitude\":-122.41286,...,\"current\":{\"time\":\"2026-07-26T04:30\",\"interval\":900,\"temperature_2m\":15.7}}", "proof": {"ok": true, "invocation_id": "inv_c23irnzhx1", "public_receipt": "https://miscsubjects.com/receipt/inv_c23irnzhx1"}} ``` `http=200 total=3.126264s` — 3.13 seconds wall clock from a laptop in California, including the Open-Meteo round trip. Three consecutive invocations of a pure `fn` row with no upstream call, timed the same way, took 3.40 s, 1.07 s and 1.59 s; the first carries TLS and connection setup. **Step 4 — the receipt.** `inv_c23irnzhx1` records actor `owner:terminal-key`, runner `http`, trace `t_jweoafmw`, `material: true`, `cost_usd: 0`, and three SHA-256 fingerprints: input, output, and the object contract. It is public and keyless: ```bash curl -s "https://miscsubjects.com/api/dispatch?confirm=inv_c23irnzhx1" # "confirmed": true, "status": "PROVEN_MATERIAL_RESULT" ``` **Step 5 — remove it.** ```bash curl -sS -X DELETE "https://miscsubjects.com/api/directory/ZZ_TEST_TEMPERATURE" \ -H "x-terminal-key: $TERMINAL_KEY" # {"ok":true,"key":"ZZ_TEST_TEMPERATURE","deleted":1} ``` A subsequent `GET /api/directory/ZZ_TEST_TEMPERATURE` returns 404. The receipt still resolves and still reports `confirmed: true` — deleting the definition does not delete the history of what it did. ## The no-restart property depends on something outside the row Nothing here caches a tool list on the caller's side, so a new row is live on the next read. That is not a general property of tool registries, and the people who run them keep filing the same bug. A registry gateway maintainer describes the failure exactly: upstream tool lists cached at registration time, stale until a manual re-registration or a full restart, with removed tools leaving dangling references inside tool groups. The Model Context Protocol has a message for this — a server that declared the `listChanged` capability SHOULD send `notifications/tools/list_changed` when its tool list changes. Two independent reports say clients ignore it. One user reproduced a dynamic-registration server against an IDE that never re-queries `tools/list`, while the same server worked in two other clients. A Microsoft engineer filed identical behaviour against a CLI client, with a repro video, noting the same product's editor extension updates immediately. "Add a capability without a restart" is therefore a claim about the whole path, not about the registry. This path has no client-side cache to invalidate because the caller fetches one contract at a time. A registry that pushes definitions into a client's context inherits that client's refresh behaviour, and the behaviour is not uniform. ## Every failure names itself, and the names are in the code | Symptom | Literal response | Cause | Fix | | --- | --- | --- | --- | | Call returns immediately, nothing ran | `{"error":"unknown_key","attempted":"ZZ_TEST_TEMPERATUR","ran":false,"did_you_mean":[…]}` | key not in the table | use a `did_you_mean` entry, or `GET /api/dispatch?ask=` | | `fn` row fails before running | `ERR:fn:unknown_target:` | `target` names a function absent from the runner map (`dispatch.js:1169`) | correct `target`, or the function was renamed in a deploy | | `fn` row fails on its own template | `ERR:fn:bad_content_json:` | the executable line of `content` is not valid JSON after substitution (`dispatch.js:1173`) | the template must be a JSON array; check for an unescaped quote in an argument | | `fn` template parses but is rejected | `ERR:fn:content_not_array` | the template is valid JSON but not an array (`dispatch.js:1174`) | wrap it: `["$1","$2"]` | | Credential-shaped `auth` never applies | request goes out with `"headers":{}` | `auth` names an environment variable that does not exist | add the secret under the exact name; the row does not change | | Auth string is malformed | `ERR:http::ERR:auth:unknown_prefix:apikey` | prefix is not one of `bearer:`, `basic:`, `headers:`, `query:`, `oauth:` (`dispatch.js:234`) | use a supported prefix | | Upstream refuses | `ERR:http:401:` | the credential exists but is rejected | rotate the secret; the row is fine | | Every call to one row fails instantly after a run of 401s | `ERR:breaker_open: — 8 consecutive auth failures; credential is dead until replaced.` | the circuit breaker tripped at 8 consecutive 401/403 (`dispatch.js:1293-1320`) | replace the credential; the breaker clears after 1 hour or on `KV delete breaker:` | | Target host unreachable | `ERR:http:fetch:` | DNS, TLS or connection failure (`dispatch.js:1285`) | check the URL in `target` | | Argument missing | URL renders with an empty slot, e.g. `&longitude=&` | fewer pipe-separated pieces than the template's `$N` slots | count the `$N` slots; extra arguments beyond the highest slot are silently discarded | | `flow` step fails | `ERR:flow:bad_step:` | a step has no `:` separating key from body (`dispatch.js:1723`) | write `KEY: args` | | Write refused, nothing changed | `{"error":"registry_hygiene_refused: missing_description","how_to_fix":"content (the docstring…) is required…","state_changed":false}` | PUT/PATCH would leave the row with empty `content` (`[key].js:142-153`) | write the `# WHAT / # ARGS / # EX` docstring | | Marking a row sensitive is refused | `{"error":"registry_hygiene_refused: high_risk_missing_schema"}` | `sensitive` set without `input_schema` | supply `input_schema` in the same call | | PATCH accepted no changes | `{"error":"no recognized fields"}` HTTP 400 | the body named only fields outside the allow-list (`[key].js:223`) | `sensitive` and `runner` are not writable through PATCH | | Token rejected on a row it should reach | `risk_ceiling:low!=` | the token pinned a contract hash and the row's contract changed | mint a fresh token against the new contract | The hygiene gate is asymmetric on purpose. `PUT` refuses any non-compliant write. `PATCH` compares the violation before and after the merge and refuses only a patch that makes a compliant row non-compliant, so the rows that predate the rule stay editable for unrelated maintenance (`[key].js:206-219`). Of 891 rows, 256 carry an `input_schema` and 63 carry `examples`. ## Where the row loses to a schema, and where a schema loses to the row | Dimension | Directory row | JSON Schema tool definition | OpenAPI 3.1 operation | MCP tool | | --- | --- | --- | --- | --- | | Argument typing before the call | none; one string, split on `\|` | full — types, enums, required, formats | full, plus content negotiation and parameter locations | full; `inputSchema` is a JSON Schema object | | Rejects a bad call without executing | no; the runner or the upstream rejects it | yes, at the validator | yes, at the gateway or generated client | yes, if the host validates | | Client code generation | none | partial | mature; the spec exists so consumers can act "without access to source code" | via generated SDKs over the schema | | Ecosystem and tooling | one implementation, this one | universal | very large | growing fast, multi-vendor | | Discovery | `?ask=` in plain words, or `?registry=1` | out of band | the document is the discovery surface | `tools/list` | | Cost in caller context | one contract, ~4.4 KB, fetched when needed | every definition, every request | n/a in-prompt; large as a document | every definition, every request unless the host defers | | Adding a capability | one INSERT, live immediately | edit the tool array, redeploy the caller | edit the document, regenerate clients | server-side change plus a `list_changed` the client may ignore | | Change safety for callers | contract hash on the receipt, detected after the fact | schema diff, detected by tooling | versioned document, diffable | schema diff, if the client re-reads | The verdict. Use a schema when a wrong call is expensive and must be stopped before it executes — money movement, destructive writes, anything where "the upstream returned 400" is already too late — or when strangers will write clients against it. Typing is not decoration there; it is the only place a bad argument is caught for free. Use a row when the surface is large, the caller is a model, the operations are mostly read-and-report, and the dominant cost is context rather than correctness. The two are not exclusive. `input_schema` is on the row for this reason: 256 rows carry one, and those are the rows that get typed when the table is projected as an MCP tool list. The row is the storage format; the schema is one projection of it. ## A row has no version number, and the receipt is where change is detectable `updated_at` is overwritten on every write. There is no version column, no history table, and no diff. What exists instead is a fingerprint computed at invocation time. `objectContractFingerprint` (`functions/_lib/object_contract.js:17-25`) hashes the fields that define the call — id, object type, runner, directory type, category, target, description, `input_schema`, auth, risk, approval requirement, status, operation semantics — and the resulting SHA-256 is stored on every receipt as `fingerprints.contract`. Which fields count was measured directly, by invoking the same row three times with an edit in between: | Edit between invocations | Invocation | Contract fingerprint | | --- | --- | --- | | — (baseline) | `inv_vbzo55gyxb` | `fcb5a4d6ccdd552994c09c96a88c6a1dc18470d2fb1b57c151b4b951e4a7342f` | | `PATCH {"examples":"[\"51.51\|-0.13\"]"}` | `inv_7s7br5887e` | `fcb5a4d6ccdd552994c09c96a88c6a1dc18470d2fb1b57c151b4b951e4a7342f` | | `PATCH {"target":"…¤t=temperature_2m,wind_speed_10m"}` | `inv_m6c161ry9u` | `da066c304231231b32002f04aebb513f8a62bed41646e4b16845cb25c8c7fadc` | Changing `examples` left the fingerprint byte-identical. Changing `target` changed it. So the hash tracks the callable contract and ignores documentation-only edits — which is the behaviour you want, and it is worth knowing rather than assuming. Two guarantees follow, and one gap. A capability token may be minted pinned to a contract hash; any invocation after the row changes is refused with `contract_changed:!=` and HTTP 409 (`dispatch.js:2128-2132`), so the caller is stopped rather than silently redirected. And every mutation is written to the append-only event log as a `DIRECTORY_MUTATE` record carrying the action, the key and the row (`[key].js:29-45`) — the change history exists even though the row does not keep it. The gap: an unpinned caller invoking a changed row gets the new behaviour with no warning and learns of it from the receipt afterwards. That is the limitation, and the reason pinning exists. It is the same distinction aderix drew about version-controlling capabilities in general — approval around the definition does not help mid-flight, because the dangerous moment is the invocation, not the edit. Receipts are engine-authored, never agent-authored, and that is not stylistic. A controlled two-condition experiment found an agent inventing a governance event that never happened and presenting it as compliance evidence when nothing else wrote the record. Here the dispatcher writes it, in the same code path that runs the call, with hashes of the actual input and output bytes. ## Sources 1. Cloudflare D1 overview — https://developers.cloudflare.com/d1/ 2. Tool use overview — Claude Docs — https://platform.claude.com/docs/en/agents-and-tools/tool-use/overview 3. Model Context Protocol — Tools (2025-06-18) — https://modelcontextprotocol.io/specification/2025-06-18/server/tools 4. JSON Schema Validation, draft 2020-12 — https://json-schema.org/draft/2020-12/json-schema-validation 5. OpenAPI Specification 3.1.0 — https://spec.openapis.org/oas/v3.1.0.html 6. modelcontextprotocol/schema.ts — the Tool interface — https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/schema/2025-06-18/schema.ts 7. Dynamic tool sync: notifications/tools/list_changed + polling fallback — https://github.com/mcpjungle/MCPJungle/issues/260 8. Kiro IDE does not handle MCP notifications/tools/list_changed — dynamic tools not refreshed — https://github.com/kirodotdev/Kiro/issues/6553 9. GitHub Copilot CLI does not dynamically load tools via tools/list_changed — https://github.com/microsoft/wassette/issues/308 10. Comment on: Agentic Engineering Patterns — https://news.ycombinator.com/item?id=47263727 11. Comment on: Polymcp – toolkit for building MCP agents that discover, inspect and orchestrate tools — https://news.ycombinator.com/item?id=46487491 12. Reduce Context Window Usage (13,341 tokens for tools alone) — https://github.com/abdlkrim-jribi/hcode/issues/4 13. Comment on: Apideck CLI – An AI-agent interface with much lower context consumption than MCP — https://news.ycombinator.com/item?id=47400262 14. GCORE_TOOLS=* advertises ~488k tokens of tool definitions — larger than most context windows — https://github.com/G-Core/gcore-mcp-server/issues/14 15. Comment on: MCP is dead; long live MCP — https://news.ycombinator.com/item?id=47381282 16. Comment on: Show HN: GitAgent – An open standard that turns any Git repo into an AI agent — https://news.ycombinator.com/item?id=47417059 17. Comment on: Agent Runs Code You Never Wrote — https://news.ycombinator.com/item?id=47579314 18. Comment on: Ask HN: How are you enforcing permissions for AI agent tool calls in production? — https://news.ycombinator.com/item?id=46747408 19. Add sanitized audit logging contract for MCP tool calls — https://github.com/rafaself/aws-mcp-gateway/issues/21 20. Row counts by type, taken from production D1 on 2026-07-26 — https://miscsubjects.com/api/dispatch?registry=1 21. Credential forms and registry hygiene across all 891 rows — https://miscsubjects.com/api/directory 22. Receipt for the first invocation of a capability created minutes earlier — https://miscsubjects.com/receipt/inv_c23irnzhx1 23. Contract size, measured across four rows of four different types — https://miscsubjects.com/api/dispatch?key=GROK_MODELS&format=markdown 24. Which row edits change the contract fingerprint, measured by three invocations — https://miscsubjects.com/api/dispatch?confirm=inv_m6c161ry9u 25. The production CREATE TABLE and column list, read back from D1 — https://miscsubjects.com/api/directory 26. cloudflare/workers-sdk — wrangler, the tool every measurement here was taken with — https://github.com/cloudflare/workers-sdk