{"uid":"cap_VHMHNrcTzKEySYUpCz3pU","slug":"expression-evaluator-variable-inspector-22a2c712","name":"Expression Evaluator – Variable Inspector","description":"Parse an expression and return the free variables it references, without evaluating it — so an agent can discover which inputs a formula needs before supplying values. A syntax error is a clean 400.","url":"https://math.openverbs.com/v1/variables","method":"POST","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method","bodyType","body"],"properties":{"body":{"type":"object","required":["expression"],"properties":{"expression":{"type":"string","maxLength":1000,"minLength":1,"description":"The expression to inspect."}},"additionalProperties":false},"type":{"type":"string","const":"http"},"method":{"enum":["POST"],"type":"string"},"bodyType":{"enum":["json","form-data","text"],"type":"string"}},"additionalProperties":false}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.004","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.004/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.004","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.004","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_2D0wknH75lT_itLbH3qum","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.004","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Inspects a mathematical or logical expression and extracts the variables contained within it","exampleAgentPrompt":"Can you inspect the expression '2*x^2 + 3*y - z' and tell me what variables are in it?","exampleUseCases":[{"title":"Formula dependency analysis","prompt":"I have the formula 'a*sin(b*t + c) + d' — can you tell me all the variables it depends on so I know what inputs I need to evaluate it?"},{"title":"Equation variable extraction for solver setup","prompt":"Before I run my equation solver, can you parse 'alpha * x^2 + beta * x + gamma = 0' and list out all the variable names it contains?"},{"title":"Checking expression inputs before evaluation","prompt":"I want to make sure I know every variable in this expression before plugging in values: '(p * q) / (r + s * t)' — what variables does it use?"}],"resultDescription":"A structured response listing all variable names (identifiers) found within the provided expression string, allowing the caller to know exactly which unknowns or parameters the expression depends on.","failureModes":["Expression string is empty or missing — returns validation error","Expression exceeds 1000 character limit — rejected with schema error","Malformed or unparseable expression — may return parse error or empty variable list","Network or service unavailability — HTTP 5xx error"],"whenToPreferThis":"Use this endpoint when you need to programmatically determine which variables or identifiers are present in a mathematical or logical expression before evaluating it, building a solver, or validating inputs. It is particularly useful in dynamic formula engines, educational tools, or symbolic math pipelines where expressions are user-supplied and the required variable bindings are unknown ahead of time.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-09-14T12:34:22.610Z","isFirstParty":false}