FactReason

Component specification

factreason_component_spec

Read-onlyIdempotent

Look up electronics component pin assignments, voltage range, package, and alternatives. Pass exact partNumber for one component or query for a capability search; partNumber takes precedence if both are supplied. For exact lookups, set responseFormat="compact" for tokenizer-measured context savings; the backward-compatible default is "full". Uses metered access and returns matches or suggestions. Confirm critical values against the manufacturer datasheet.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`query`	No	Free-text capability search, e.g. "3.3V ARM MCU with SPI"
`apiKey`	No	Your FactReason API key, from factreason_create_key. Pass it here when your MCP client cannot set the Authorization: Bearer header on this connection; if the header is set, omit this. Never pass a key that belongs to someone else.
`partNumber`	No	Exact part number, e.g. "STM32F401RE"
`responseFormat`	No	Use compact for an exact part lookup; full preserves the legacy data response	full

Output Schema

TableJSON Schema

Name	Required	Description	Default
`data`	No
`hint`	No
`found`	No
`compact`	No
`message`	No
`results`	No
`partNumber`	No
`provenance`	No
`qualityScore`	No
`tokenMetrics`	No
`totalMatched`	No
`nearestMatches`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 4, 2026

addedInput schema / properties / apiKey

Added value: +{
+  "description": "Your FactReason API key, from factreason_create_key. Pass it here when your MCP client cannot set the Authorization: Bearer header on this connection; if the header is set, omit this. Never pass a key that belongs to someone else.",
+  "maxLength": 128,
+  "minLength": 1,
+  "type": "string"
+}

Changed6 schema fields changedAug 17, 2026

addedInput schema / properties / responseFormat

Added value: +{
+  "default": "full",
+  "description": "Use compact for an exact part lookup; full preserves the legacy data response",
+  "enum": [
+    "full",
+    "compact"
+  ],
+  "type": "string"
+}

removedOutput schema / properties / compact / additionalProperties
```
Removed value: -true
```
changedOutput schema / properties / compact / type
```
Previous value: -"object"New value: +"string"
```

addedOutput schema / properties / provenance

Added value: +{
+  "additionalProperties": true,
+  "type": "object"
+}

addedOutput schema / properties / qualityScore
```
Added value: +{
+  "type": "number"
+}
```

addedOutput schema / properties / tokenMetrics

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "compactTokens": {
+      "type": "number"
+    },
+    "encoding": {
+      "const": "o200k_base",
+      "type": "string"
+    },
+    "fullTokens": {
+      "type": "number"
+    },
+    "reductionPct": {
+      "type": "number"
+    },
+    "savedTokens": {
+      "type": "number"
+    }
+  },
+  "type": "object"
+}

Changed7 schema fields changedAug 14, 2026

addedInput schema / additionalProperties
```
Added value: +false
```

addedInput schema / anyOf

Added value: +[
+  {
+    "required": [
+      "partNumber"
+    ]
+  },
+  {
+    "required": [
+      "query"
+    ]
+  }
+]

changedInput schema / properties / partNumber / description

Previous value: -"Exact part number, e.g. \"STM32F401RE\", \"ESP32-WROOM-32E\""New value: +"Exact part number, e.g. \"STM32F401RE\""

addedInput schema / properties / partNumber / minLength
```
Added value: +1
```

changedInput schema / properties / query / description

Previous value: -"Alternative: free-text search, e.g. \"3.3V ARM MCU with SPI\""New value: +"Free-text capability search, e.g. \"3.3V ARM MCU with SPI\""

addedInput schema / properties / query / minLength
```
Added value: +1
```

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "properties": {
+    "compact": {
+      "additionalProperties": true,
+      "type": "object"
+    },
+    "data": {
+      "additionalProperties": true,
+      "type": "object"
+    },
+    "found": {
+      "type": "boolean"
+    },
+    "hint": {
+      "type": "string"
+    },
+    "message": {
+      "type": "string"
+    },
+    "nearestMatches": {
+      "items": {
+        "additionalProperties": true,
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "partNumber": {
+      "type": "string"
+    },
+    "results": {
+      "items": {
+        "additionalProperties": true,
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "totalMatched": {
+      "type": "number"
+    }
+  },
+  "type": "object"
+}

First observedAug 14, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations cover the safety profile (readOnly, idempotent, non-destructive), and the description adds what annotations cannot: metered access, that results may be matches or suggestions rather than exact hits, and a datasheet-verification caveat. The compact/full output-shape tradeoff is also disclosed. Minor omission is any note on rate limits or what 'suggestions' implies for reliability.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads the capability, then mode selection, then format, then the caveat. Four sentences, each carrying distinct information. Slightly dense but no filler; the caveat sentence is arguably the least load-bearing but is defensible for engineering data.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values need not be described, and the auth parameter is documented in the schema. The description supplies mode selection, precedence, metered access, and a correctness caveat, leaving little an agent needs to call it correctly. A note on pagination or result-count limits would close the remaining gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds genuinely new meaning: the precedence order between partNumber and query, and the tokenizer-measured context savings of responseFormat=compact versus the backward-compatible full default. That is substantive guidance beyond the enum and property docs.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('look up electronics component pin assignments, voltage range, package, and alternatives') and enumerates the exact fields returned. It is clearly distinct from every sibling, which are all API-lifecycle tools (breaking changes, schema, auth, deprecation).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit routing rule between the two modes ('Pass exact partNumber for one component or query for a capability search') and resolves the conflict case ('partNumber takes precedence if both are supplied'). No sibling alternatives are named, but none of the siblings overlap functionally, so this gap is minor.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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